* Departments of Neurobehavioral Toxicology and
Analytical Chemistry, Medical Institute of Environmental Hygiene, Auf'm Hennekamp 50, D-404225 Düsseldorf, Germany
Received January 10, 2000; accepted June 29, 2000
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key Words: polychlorinated biphenyls; vitamin D; development; steroids; rat.
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
In addition to effects on liver enzymes and on the nervous system, PCBs are known to interact with thyroid hormones and gonadal steroids (Brouwer et al., 1995; Safe 1995
). For instance, the non-ortho-chlorinated, coplanar congener PCB 77 binds to the estrogen receptor in a competitive manner and can modulate ligand-regulated processes (Nesaretnam et al., 1996
). Reductions in serum testosterone concentrations have been found in rats treated with another coplanar congener, PCB 169 (Yeowell et al., 1987
). PCB 169 also impaired estradiol-induced up-regulation of uterine estrogen receptors as did the ortho-chlorinated compound PCB 153 (Patnode and Curtis, 1994
). Technical mixtures of PCBs, which consist mainly of ortho-chlorinated congeners, are reported to increase the concentration of estrone sulfate in exposed pregnant guinea pigs (Lundkvist et al., 1987
). Moreover, they reduce the binding of progesterone to its receptor in rabbit uterine mucosa (Lundholm, 1988
), alter the activities of several testosterone hydroxylases (Haake-McMillan and Safe, 1991
), and mimic the effects of estradiol on uterine weights and the gonadotropin response in anterior pituitary cells (Jansen et al., 1993
). Hydroxylated metabolites of PCBs also bind to estrogen receptors (Connor et al., 1997
; Korach et al., 1988
; Ramamoorthy et al., 1997
). Both PCB congeners and metabolites can produce either estrogenic or anti-estrogenic effects, depending on the test systems (Connor et al., 1997
; Jansen et al., 1993
).
Several steps of the synthesis and metabolism of steroids in general involve cytochrome P450-dependent enzymes (Vanden Bossche 1992). Since many isoforms of this group, including those that catalyze the metabolism of sex steroids, are influenced by PCBs (Haake-McMillan and Safe, 1991
; Safe 1990
, Yeowell et al., 1987
, 1988
), PCB-induced actions on steroids other than gonadal hormones are not unlikely. In the present study PCB-induced effects on levels of vitamin D3 metabolites were examined. Vitamin D3, or cholecalciferol, is a secosteroid, which means one of the rings in the steroid molecule is broken. It is converted into its active form, 1,25-(OH)2-cholecalciferol (1,25-D), in two hydroxylation steps, the first occurring in the liver and the second in the kidney (review in Kumar, 1991). Both steps are catalyzed by cytochrome P450-containing enzymes, the 25-hydroxylase (CYP27) and the 1
-hydroxylase, which has been referred to CYP27B1 (Jones et al., 1998
).
The classical targets of 1,25-D are those directly related to calcium homeostasis in the body and comprise the enterocytes in the intestine, the osteoblasts in bone, and the distal tubule cells in the kidney. Recently, binding sites for 1,25-D were found in several non-classical target tissues, e.g. parathyroid glands, adrenals, pituitary, male and female gonads, islet cells in the pancreas, skin, heart, vascular and skeletal muscles, lung, liver, and brain (reviews in Bouillon et al., 1995; Bringhurst et al., 1998; Jones et al., 1998; Walters 1997). In addition, 1,25-D has immune effects (Hewison and O'Riordan, 1997). It regulates cell differentiation and proliferation and, consequently, exerts anti-tumor activity (Bouillon et al., 1995
). Like other steroids, 1,25-D has genomic and non-genomic actions, the latter of which were studied particularly in the intestine, osteoblasts, muscles, and parathyroid (Bouillon et al., 1995
). In myoblasts, a rapid activation of adenylate cyclase and protein kinase C was found (De Boland and Boland 1994
).
PCBs have known effects on calcium homeostasis and transport in neurons (e.g., Kodavanti et al., 1998) and in microsomes of the sarcoplasmic reticulum (Wong and Pessah, 1996, 1997
). Therefore, any change in concentrations of 1,25-D by PCBs may lead to disturbance of calcium balance resulting in reduced availability of calcium to cells; this may exacerbate effects on calcium-mediated processes.
Most studies have used either technical mixtures or single congeners to investigate PCB-induced effects. Neither approach accurately reflects environmental exposure of animals and humans, because the pattern of PCB congeners differs in technical mixtures and environmental samples (Safe 1994). Therefore, a mixture of PCBs reconstituted according to the pattern found in human milk was used in the present study. The overall PCB concentration in breast milk is highly correlated with the concentration in cord plasma and plasma values in children at the age of 42 months (Lanting et al., 1998
), reflecting their PCB body burden. This analysis was based on four selected PCB congeners for which very similar patterns were reported in all three matrices. Since 1,25-D has been shown to be produced by rat placental tissue in vitro (Tanaka et al., 1979
) and, in contrast to the adult rat, also by the fetal rat liver (Takeuchi et al., 1994
), concentrations of 25-D and 1,25 were measured in PCB-treated rat dams and pups. In addition, measures of internal exposure, reproduction, and development of the offspring were included.
![]() |
MATERIALS AND METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
On PND 0, litter sizes and weights were determined and the pups were examined for malformations. Measurement of pup weights was repeated on PND 5, 10, 15, and 21 when the offspring were weaned from their mothers. On PND 0, 3 dams/group were sacrificed with their litters. Brains and perirenal adipose tissue were removed for analyses of internal PCB concentrations, and blood samples were taken by heart puncture for determination of 25-D and 1,25-D. For analyses of PCBs, brains of all pups from a litter were pooled. Additional blood samples were collected from dams (57/group) and female offspring (78/group) on PND 21. In accordance with accepted standards (Holson and Pierce 1992), only one pup per litter was taken for collection of the samples. The number of blood samples for determination of vitamin D metabolites was limited since samples of other pups were needed for the analysis of sex steroids. For determination of internal exposure to PCBs on PND 21, 3 litters/group were used and brain and fat tissue samples of 2 female pups/litter were pooled for the analyses. Animals were randomly selected for all dissections. On PND 21, only female offspring were sacrificed, in order to save the males for behavioral studies.
PCB Mixture
The mixture of PCB congeners was reconstituted according to published results of several studies on the PCB pattern in human breast milk (Duarte-Davidson et al., 1992; Jensen 1991
; Noren and Lunden 1991
; Safe et al., 1985
; Schulte and Malisch 1984
). PCB congeners were obtained from Promochem (Wesel, Germany). They had a guaranteed purity of > 99.8% and were free of dibenzofurans. Congeners were selected that met the criteria of consistent detection in at least 3 of the 5 sources in a mean percentage of more than 2% of the whole PCB content. The mono-ortho-chlorinated congeners PCB 28 and PCB 105, as well as the di-ortho-chlorinated PCB 101 were also included, because they are also frequently and consistently detected in breast milk and adipose tissue in the reports given above. In addition, the coplanar congeners PCBs 77, 126, and 169 were added in quantities reported for human milk (Dewailly et al., 1991
; Noren and Lunden 1991
) to include congeners of all classes, coplanar, mono- and di-ortho-chlorinated PCBs. The composition of the resulting reconstituted mixture is shown in Table 1
. The proportions of the congeners given in Table 1
are the average values of the concentrations detected in the reports cited above.
|
Determination of 25-D and 1,25-D
Serum concentrations of 25-D and 1,25-D were determined in duplicate by standard commercial test kits (Immundiagnostik GmbH, Bensheim, Germany). For measurement of 25-D, samples were analyzed using a competitive protein-binding assay (CPBA), with vitamin D3 binding protein from goat serum and 3H-25-D as tracer after extraction with acetonitrile. Non-specific binding was 4.933% and the intraassay and interassay variations were 2.7% and 14.0%, respectively. The detection limit was 0.542 ng/ml. The level of 1,25-D was determined using a radio receptor assay (RRA), after extraction on a silica gel column (Extrelut-1) and separation from other vitamin D3 metabolites on a second silica gel column (Bakerbond spe). Non-specific binding was 7.5%, and the intra-assay and inter-assay variations were 4.2% and 15.0%, respectively. The detection limit was 1.135 pg/ml. Samples were analyzed in a blind fashion.
Analysis of PCB Tissue Concentrations
PCB exposure levels were analyzed in the complete brain, as well as in perirenal adipose tissue, by gas chromatography with electron capture detection (GC-ECD system, HRGC Mega 2, Fisons, Mainz, Germany). Briefly, after thawing, the brain samples were ground with a potter homogenizer (B. Braun, Melsungen, Germany). Adipose tissue and brains were vortexed with formic acid in a test tube. Afterwards, the PCBs were extracted by solvent extraction with n-heptane from the tissue-formic acid mixtures. The n-heptane extracts were purified by silica gel chromatography using petroleum ether as the mobile phase. The gas chromatographic separation of the PCBs was carried out on 2 capillary columns of different polarity (DB5, 30 m x 0.32 mm x 0.25 µm, and DB1701, 30 m x 0.32 mm x 0.25 µm; both from J and W Scientific, Köln, Germany). Further details concerning the analytical procedures will be published in a forthcoming paper. The 14 PCB congeners used to create the RM, and additionally PCB 52, were measured in the different specimens. Determination of PCB 52 was included since it is always measured in routine analysis by the laboratory. PCB detection limits in brain samples from PND 0 and PND 21 were between 0.005 and 0.01 mg/kg. The range of detection limits in adipose samples was 0.050.1 mg/kg (PND 0 samples) and 0.130.25 mg/kg (PND 21 samples). The precision was > 90% in all cases.
Statistical Analysis
Statistical analysis was conducted using the SAS statistical package (SAS Institute Inc., Cary, NC). Statistical analyses were litter-based. Reproductive measures like litter size and weight were evaluated by analysis of variance (ANOVA). Mortality rates were evaluated with the Chi2 test. Body weights of pups during the suckling period were analyzed by ANOVA, with repeated measures on the day factor. For post hoc comparisons, the REGWQ test (Ryan, Einot, Gabriel, Walsh multiple range test; SAS/STAT User's Guide, 1990) was calculated. The SAS statistical package was also used for fitting internal PCB concentrations to linear regression models. Because of the non-normal distribution of hormone values, the non-parametric Mann-Whitney U-test (2-tailed) was used for comparisons of groups (Siegel 1956). To test whether hormonal effects were dose-dependent, orthogonal trends were determined according to the non-parametric method of Marascuilo and McSweeney (Bortz et al., 1990
). Probabilities of p < 0.05 were considered significant.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
Concentrations of Vitamin D3 Metabolites in Offspring
Results for the serum concentrations of 25-D and 1,25-D in offspring are shown in Figure 2. At weaning, the RM40 group exhibited decreased serum levels of 25-D, which were 2025% lower than values in all other groups. These differences were significant (U-test, RM40 vs. controls: U = 2, p < 0.01; RM40 vs. RM05: U = 11, p < 0.05; RM40 vs. RM20: U = 8, p < 0.05). The offspring of the RM40 group also had significantly reduced serum concentrations of 1,25-D (U-test, RM40 vs. controls: U = 1 2, p < 0.05; RM40 vs. RM05: U = 11, p < 0.05; RM40 vs. RM20: U = 11, p < 0.05). Percentages of decrease were about 15% and 33% in RM20 and RM40 rats, respectively, when compared to controls, while the RM05 offspring exhibited an increase of about 13% in comparison to controls. The linear trend describing the dose dependency of PCB-induced effects on 1,25-D in offspring was significant (Chi2 = 5.01, p < 0.05).
|
|
|
|
|
PCB concentrations in the adipose tissue of dams were about 50 times higher than levels in the brain at birth, while at weaning, there was a factor of about 150 because of the decrease in PCB concentrations in the brain during lactation. In female offspring, the ratio of adipose tissue concentrations to brain concentrations was about 7 on PND 21.
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Previous work on PCB-induced effects in vitro and in vivo revealed exposure-related changes in intracellular calcium concentrations and calcium uptake by mitochondria and microsomes together with alterations in calcium-dependent signal transduction processes (Kodavanti et al., 1998, 1996
, and 1993). Also, transient inhibition of excitatory postsynaptic potentials by PCB 52, which could be antagonized by the L-type calcium channel blocker nifedipine, was described in slices from the ventral hippocampus (Hong et al., 1998
). Furthermore, ryanodine receptor-mediated calcium transport was altered by PCBs in microsomes from skeletal and cardiac muscles (Wong and Pessah, 1996
, 1997
). Similar influences on calcium homeostasis in liver, neural tissue, and heart have been found after treatment with 2,3,7,8-TCDD (Al-Bayati et al., 1988
; Canga et al., 1988
; Hanneman et al., 1996
). This raises the question of whether PCB-induced reductions in 1,25-D serum concentrations contribute to disturbances in calcium homeostasis and calcium-dependent functions. While it is unlikely that 1,25-D is involved in the effects of PCBs in the in vitro systems mentioned above, the situation is different in vivo. An altered calcium balance due to reduced levels of 1,25-D in vivo may well modify PCB actions in the cellular systems which were examined in vitro, as decreases in 1,25-D may result in a reduced availability of calcium to these targets, thereby exacerbating the described effects. Further studies are needed to clarify PCB-induced effects on cellular systems after exposure in vivo and the consequences of reduced availability of calcium because of reduced 1,25-D concentrations.
In addition, it has been shown that 1,25-D, like other steroid hormones, has genomic and non-genomic effects (reviews, e.g., in DeBoland and Boland 1994; Bouillon et al., 1995; Norman 1997). Non-genomic, rapid actions have been found in several cell types involving voltage-gated Ca2+ channels (Caffrey and Farach-Carson 1989), direct interaction with PKC (Slater et al., 1995
) or rapid changes in the intracellular location of PKC (Bhatia et al., 1996
). Thus, rapid actions of 1,25-D involve processes similar to those which, as described above, have been shown to be affected by PCBs in other cell types. PCBs are also reported to influence functions and targets for which an action of 1,25-D is assumed. These include bone calcium metabolism and kidney function (Andrews 1989
), testes (Hany et al., 1999
), keratinocytes (Vos and Beems 1971
), T lymphocytes (Tryphonas et al., 1989
), insulin release (Fischer et al., 1996
), adrenal medulla cells (Messeri et al., 1997
), and skeletal muscles (Wong and Pessah 1996
). Binding sites for 1,25-D were recently detected in many of these non-classical target tissues which, like the ovaries, depend directly on 1,25-D (Kwiecinski et al., 1989a
), while in others, like the testes, substitution of calcium is sufficient (Kwiecinski et al., 1989b
). Obviously, there are many parallels in targets for 1,25-D and PCBs, and it remains to be determined whether these parallels are merely due to a direct action of PCBs on calcium homeostasis as described in vitro, whether reduced levels of 1,25-D in vivo result in additional influences on calcium-dependent processes, or whether they even mediate some of the PCB effects. For instance, reductions in 1,25-D may be involved in the PCB-related hypotonicity observed in human children (Rogan et al., 1986
), since skeletal muscle myopathies were found in 1,25-Ddeficient humans and rats, which normalized after treatment with vitamin D (Walters 1997
).
The calcium balance in vivo is of particular importance during pregnancy and development of the progeny. To meet the additional requirements for calcium in fetuses, there is an increase in calcium absorption in maternal intestine (Heaney and Skillman 1971) as well as in bone resorption in rats, sheep, and humans (Miller et al., 1982
). In addition, the conversion of 25-D to 1,25-D is increased during gravidity in rats (Paulson et al., 1990
) and sheep (Ross and Dorsey, 1991
). Concentrations of 25-D and 1,25-D are lower in offspring than in dams in several species, and both steroids are transferred via the placenta; however, this transport appears to be small (Ross et al., 1990
). In humans maternal and fetal levels of 1,25-D are correlated (Delvin et al., 1988
), but correlations are otherwise weak because of the production of 1,25-D in the placenta (Tanaka et al., 1979
), fetal kidney and liver (Takeuchi et al., 1994
). It is likely, that PCBs, as they are transferred across the placental barrier, influence concentrations of 1,25-D in fetal tissues. Therefore, further measurements should examine possible reductions of 1,25-D levels in fetal matrices.
The consequences of a reduced supply with 25-D and 1,25-D during gestation and lactation are still uncertain. In mice lacking the receptor for 1,25-D impairments of development and growth were found only after weaning, even when weaning was delayed, suggesting the presence of a substituting factor in milk (Yoshizawa et al., 1997). In addition, vitamin D-deficient rats gave birth to normally developed offspring, although their reproduction rate was very low (Halloran and DeLuca (1979
). Normal bone mineralization was found in rat pups born to vitamin D-deficient dams (Halloran and DeLuca, 1981
) and transplacental gradients of calcium and phosphate were not affected by vitamin D deficiency (Brommage and DeLuca 1984
). This suggests that pregnant rats can deplete their skeleton minerals sufficiently to adjust to the enhanced calcium requirements of the fetuses at the end of gestation (Care 1997
). It is assumed that calcium transport across the placenta is mediated by parathyroid hormone-related protein (PTHrP) as this protein stimulates the transfer in sheep, while PTH itself is not effective (Rodda et al., 1989). In addition, in mice lacking the PTHrP gene, transplacental transport of calcium is insufficient (Kovacs et al., 1996
), suggesting that normal fetal calcium supply is achieved by PTHrP and not by 1,25-D. On the other hand, congenital rickets has been described in human children (Moncrieff and Fadahunsi 1974
), and decreased concentrations of 1,25-D in fetal blood are associated with reduced body size and low bone mineral content (Namgung et al., 1993
). In rats, diminished growth of longitudinal bones was found in neonatal offspring born to vitamin D-deficient dams (Miller et al., 1983
). Also, in 1,25-D receptor knockout mice the gene expression of calbindin-D9K was markedly decreased in the kidney and intestine at weaning (Yoshizawa et al., 1997
). Under normal conditions 1,25-D causes an increase in this calcium-binding protein at the end of gestation in rat fetuses, resulting in an adult-like distribution pattern that most likely serves to prepare the offspring for the transition from placental transfer of calcium to intestinal absorption (Delorme et al., 1979
). Thus, in the absence of gross abnormalities described in 1,25-D receptor null mutants, there may be subtle changes in developmental actions of 1,25-D at late gestation and during lactation. This is particularly so since interactions of 1,25-D with thyroid hormones and sex steroids have now been reported (Suarez et al., 1998
; Walters 1997
) that are known to exert influences on development (McEwen 1994
; Porterfield and Hendrich 1994). Because of the incomplete and controversial data, the role of 1,25-D and the consequences of its lack during development is difficult to assess. Reduced levels of 1,25-D caused by exposure to PCBs and other chlorinated hydrocarbons may affect any process in which 1,25-D takes part. In this framework, it is noteworthy that hypomineralization in teeth of children correlated with PCDD and PCDF values in breast milk (Alaluusua et al., 1996
). Also, the contribution of reduced levels of 25-D and 1,25-D to decreases in body weights at the highest exposure level and increases in mortality in both of the high-exposure groups seen in the present investigation remain to be elucidated.
In contrast to long-lasting effects of the reconstituted PCB mixture on testosterone concentrations in serum (Hany et al., 1999), effects on 25-D and 1,25-D levels appear to be transient, since pilot measurements of sera from adult males, which were littermates of the rats studied by Hany et al., indicated no differences between treatment groups (data not shown).
The internal PCB concentrations in adipose tissue and brain showed a linear relation to dosages in diets. Due to a technical failure, no fat concentrations could be determined in the RM05 and RM20 groups of the offspring. However, because of the linear relationship, one might expect values of about 7.5 and 30 µg/g in the RM05 and RM20 groups, respectively. PCB concentrations were comparable in brains of dams and offspring at birth, but decreased in dams during lactation, while levels in brains of the offspring increased in this phase because of the ongoing exposure by nursing. During lactation PCBs are mobilized from body stores of the dam and transferred to the offspring via milk. Since milk transfer exceeds the placental transfer in all species so far investigated by two to three orders of magnitude, this results in higher tissue concentrations in weanling pups than in fetuses (e.g. Masuda et al., 1979; Takagi et al., 1986; Montesissa et al., 1992; Vodicnik 1986).
In the present study, PCB values in the adipose tissue of dams were only slightly diminished during lactation. This suggests that during nursing, PCBs are mobilized first from other compartments than the adipose tissue in rats, which is supported by the decrease of PCB values detected in brains. Numerous studies in different species have reported that the depot in the adipose tissue is a deep compartment from which persistent PCB congeners are less rapidly removed than from several other soft tissues (e.g., Lutz et al., 1977; Morales et al., 1979). At the lowest exposure level used in the present study (RM05) even an increase was seen, which may be due to a redistribution of ingested PCBs after the termination of PCB feeding in this group. At weaning PCB concentrations in the adipose tissue were much lower in offspring than in dams, most likely because of the shorter duration of exposure.
It is remarkable that even at the lowest treatment level significant reductions of 1,25-D could be detected. The internal exposure levels in adipose tissue from dams of this group (RM05) are about 10100 times higher than median values of current PCB concentrations in human populations (Brunn et al., 1990; Stellman et al., 1998
). For persons at the upper tail of the distribution, these values decrease to 325.
In conclusion, exposure to a reconstituted PCB mixture which reflects the congener pattern of breast milk resulted in dose-dependent reductions in serum concentrations of the steroids 25-D and 1,25-D in rat dams and offspring. However, the biological significance of these decreases is uncertain and remains to be evaluated.
![]() |
ACKNOWLEDGMENTS |
---|
![]() |
NOTES |
---|
1 To whom correspondence should be addressed. Fax +49 211 3389 331. E-mail: lilien{at}rz.uni-duesseldorf.de.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Al-Bayati, Z. A., Murray, W. J., Pankaskie, M. C., and Stohs, S. J. (1988). 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) induced perturbation of calcium distribution in the rat. Res. Commun. Chem. Pathol. Pharmacol. 60, 4756.[ISI][Medline]
Ando, M., Saito, H., and Wakisaka, I. (1986). Gas chromatographic and mass spectrometric analysis of polychlorinated biphenyls in human placenta and cord blood. Environ. Res. 41, 1422.[ISI][Medline]
Andrews, J. E. (1989). Polychlorinated biphenyl (Aroclor 1254)-induced changes in femur morphometry calcium metabolism and nephrotoxicity. Toxicology 57, 8396.[ISI][Medline]
Ballschmitter, K., and Zell, M. (1980). Analysis of polychlorinated biphenyls (PCB) by glass capillary gas chromatography. Fresenius Z. Anal. Chem. 302, 2031.[ISI]
Bhatia, M., Kirkland, J. B., and Meckling-Gill, K. A. (1996). 1,25-Dihydoxyvitamin D3 primes acute promyelocytic cells for TPA-induced monocytic differentiation through both PKC and tyrosine phosphorylation cascades. Exp. Cell Res. 222, 6169.[ISI][Medline]
Bortz, J., Lienert, G. A., and Boehnke, K. (1990). Verteilungsfreie Methoden in der Biostatistik. Springer Verlag, Berlin.
Bouillon, R., Okamura, W. H., and Norman, A. W. (1995). Structure-function relationships in the vitamin D endocrine system. Endocr. Rev. 16, 200257.[ISI][Medline]
Bringhurst, F. R., Demay, M. B., and Kronenberg, H. M. (1998). Hormones and disorders of mineral metabolism. In Williams Textbook of Endocrinology (J. D. Wilson, D. W. Foster, H. M. Kronenberg, and P. R. Larsen, Eds.), pp. 11551209. W.B. Saunders, Philadelphia.
Brommage, R., and DeLuca, H. F. (1984). Placental transport of calcium and phosphorus is not regulated by vitamin D. Am. J. Physiol. 246, F526F529.[Medline]
Brouwer, A., Ahlborg, U. G., Van den Berg, M., Birnbaum, L. S., Boersma, E. R., Bosveld, B., Denison, M. S., Gray, L. E., Hagmar, L., Holene, E., Huisman, M., Jacobson, S. W., Jacobson, J. L., Koopman-Esseboom, C., Koppe, J. G., Kulig, B. M., Morse, D. C., Muckle, G., Peterson, R. E., Sauer, P. J. J., Seegal, R. F., Smits-Van Prooije, A. E., Touwen, B. C. L., Weisglas-Kuperus, N., and Winneke, G. (1995). Functional aspects of developmental toxicity of polyhalogenated aromatic hydrocarbons in experimental animals and human infants. Eur. J. Pharmacol. 293, 140.[Medline]
Brunn, H., Georgii, S., and Prucha, J. (1990). Polychlorierte Biphenyle (PCB) im menschlichen Fettgewebe. Z. Lebensm. Unters. Forsch. 190, 108111.[ISI][Medline]
Caffrey, J. M., and Farach-Carson, M. C. (1989). Vitamin D3 metabolites modulate dihydropyridine-sensitive calcium currents in clonal rat osteosarcoma cells. J. Biol. Chem. 264, 2026520274.
Canga, L., Levi, R., and Rifkind, A. B. (1988). Heart as a target organ in 2,3,7,8-tetrachlorodibenzo-p-dioxin toxicity: Decreased ß-adrenergic responsiveness and evidence of increased intracellular calcium. Proc. Natl. Acad. Sci. U.S.A. 85, 905909.[Abstract]
Care, A. D. (1997). Vitamin D in pregnancy, the fetoplacental unit, and lactation. In Vitamin D (D. Feldman, F. H. Glorieux, and J. W. Pike, Eds.), pp. 437446. Academic Press, San Diego.
Connor, K., Ramamoorthy, K., Moore, M., Mustain, M., Chen, I., Safe, S., Zacharewski, T., Gillespy, B., Joyeux, A., and Balaguer, P. (1997). Hydroxylated polychlorinated biphenyls (PCBs) as estrogens and antiestrogens: Structure-activity relationships. Toxicol. Appl. Pharmacol. 145, 111123.[ISI][Medline]
De Boland, A. R., and Boland, R. L. (1994). Non-genomic transduction pathway of vitamin D in muscle. Cell Signal 6, 717724.[ISI][Medline]
Delorme, A. C., Marche, P. G., and Garel, J. M. (1979). Vitamin D-dependent calcium-binding protein. Changes during gestation, prenatal and postnatal development in rats. J. Dev. Physiol. 1, 181194.[Medline]
Delvin, E. E., Gilbert, M., Pere, M. C. and Garrel, J. M. (1988). In vivo metabolism of calcitriol in the pregnant rabbit doe. J. Dev. Physiol. 10, 451459.[ISI][Medline]
Dewailly, E., Weber, J. P., Gingras, S., and Laliberte, C. (1991). Coplanar PCBs in human milk in the province of Quebec, Canada: Are they more toxic than dioxin for breast fed infants? Bull. Environ. Contam. Toxicol. 47, 491498.[ISI][Medline]
Duarte-Davidson, R., Harrad, S. J., Allen, S. C., and Jones, K. C. (1992). The relative contribution of individual PCBs, PCDDs, and PCDFs to toxic equivalent values derived from bulked human breast milk samples from the U.K. Chemosphere 25, 16531663.[ISI]
Fischer, L. J., Zhou, H.-R., and Wagner, M. A. (1996). Polychlorinated biphenyls release insulin from RINm5F cells. Life Sci. 59, 20412049.[ISI][Medline]
Haake-McMillan, J. M., and Safe, S. H. (1991). Neonatal exposure to Aroclor 1254: Effects on adult hepatic testosterone hydroxylase activities. Xenobiotica 21, 481489.[ISI][Medline]
Halloran, B. P., and DeLuca, H. F. (1979). Vitamin D deficiency and reproduction in rats. Science 204, 7374.[ISI][Medline]
Halloran, B. P., and DeLuca, H. F. (1981). Effect of vitamin D deficiency on skeletal development during early growth in the rat. Arch. Biochem. Biophys. 209, 714.[ISI][Medline]
Hanneman, W. H., Legare, M. E., Barhoumi, R., Burghardt, R. C., Safe, S. H., Tiffany-Castiglioni, E. (1996). Stimulation of calcium uptake in cultured rat hippocampal neurons by 2,3,7,8-tetrachlorodibenzo-p-dioxin. Toxicology 112, 1928.[ISI][Medline]
Hany, J., Lilienthal, H., Sarasin, A., Roth-Härer, A., Fastabend, A., Dunemann, L., Lichtensteiger, W., and Winneke, G. (1999). Developmental exposure of rats to a reconstituted PCB mixture or Aroclor 1254: Effects on organ weights, aromatase activity, sex hormone levels, and sweet preference behavior. Toxicol. Appl. Pharmacol. 158, 231243.[ISI][Medline]
Heaney, R. D., and Skillman, T. G. (1971). Calcium metabolism in normal human pregnancy. J. Clin. Endocrinol. Metab. 33, 661670.[ISI][Medline]
Hewison, M., and O'Riordan, J. L. (1997). Immunomodulatory and cell differentiation effects of vitamin D. In Vitamin D (D. Feldman, F. H. Glorieux, and J. W. Pike, Eds.), pp. 447462. Academic Press, San Diego.
Holson, R. R., and Pearce, B. (1992). Principles and pitfalls in the analysis of prenatal treatment effects in multiparous species. Neurotoxicol. Teratol. 14, 221228.[ISI][Medline]
Hong, S. J., Grover, C. A., Safe, S. H., Tiffany-Castiglioni, E., and Frye, G. D. (1998). Halogenated aromatic hydrocarbons suppress CA1 field excitatory postsynaptic potentials in rat hippocampal slices. Toxicol. Appl. Pharmacol. 148, 713.[ISI][Medline]
Jansen, H. T., Cooke, P. S., Porcelli, J., Liu, T.-C., Hansen, L. G. (1993). Estrogenic and antiestrogenic actions of PCBs in the female rat: In vitro and in vivo studies. Reprod. Toxicol. 7, 237248.[ISI][Medline]
Jensen, A. A. (1991). Levels and trends of environmental chemicals in human milk. In Chemical Contaminants in Human Milk (A. A. Jensen and S. A. Slorach, Eds.), pp. 45198. CRC Press, Boca Raton, FL.
Jones, G., Strugnell, S. A., and DeLuca, H. F. (1998). Current understanding of the molecular actions of vitamin D. Physiol. Rev. 78, 11931231.
Kodavanti, P. R., Derr-Yellin, E. C., Mundy, W. R., Shafer, T. J., Herr, D. W., Barone, S., Choksi, N. Y., MacPhail, R. C., and Tilson, H. A. (1998). Repeated exposure of adult rats to Aroclor 1254 causes brain region-specific changes in intracellular Ca2+ buffering and protein kinase C activity in the absence of changes in tyrosine hydroxylase. Toxicol. Appl. Pharmacol. 153, 186198.[ISI][Medline]
Kodavanti, P. R., Ward, T. R., McKinney, J. D., and Tilson, H. A. (1996). Inhibition of microsomal and mitochondrial Ca2+ sequestration in rat cerebellum by polychlorinated biphenyl mixtures and congeners. Structure-activity relationships. Arch. Toxicol. 70, 150157.[ISI][Medline]
Kodavanti, P. R., Shin, D.-S., Tilson, H. A., and Harry, G. S. (1993). Comparative effects of two polychlorinated biphenyl congeners on calcium homeostasis in rat cerebellar granule cells. Toxicol. Appl. Pharmacol. 123, 97106.[ISI][Medline]
Korach, K. S., Sarver, P., Chae, K., McLachlan, J. A., and McKinney, J. D. (1988). Estrogen receptor-binding activity of polychlorinated hydroxybiphenyls: Conformationally restricted structural probes. Mol. Pharmacol. 33, 120126.[Abstract]
Kovacs, C. S., Lanske, B., Hunzelman, J. L., Guo, J., Karaplis, A. C., and Kronenberg, H. M. (1996). Parathyroid hormone-related protein (PTHrP) regulates fetal-placental calcium transport through a receptor distinct from the PTH/PTHrP receptor. Proc. Natl. Acad. Sci. U.S.A. 93, 1523315238.
Kumar, R. (1991). Vitamin D and calcium transport. Kidney Int. 40, 11771189.[ISI][Medline]
Kwiecinski, G. G., Petrie, G. I., and DeLuca, H. F. (1989a). 1,25-Dihydroxyvitamin D3 restores fertility of vitamin D-deficient female rats. Am. J. Physiol. 256, E483E487.
Kwiecinski, G. G., Petrie, G. I., and DeLuca, H. F. (1989b). Vitamin D is necessary for reproductive functions in the male rat. J. Nutr. 119, 741744.[ISI][Medline]
Lanting, C. I., Fidler, V., Huisman, M., and Boersma, E. R. (1998). Determinants of polychlorinated biphenyl levels in plasma from 42-month-old children. Arch. Environ. Contam. Toxicol. 35, 135139.[ISI][Medline]
Lundholm, C. E. (1988). The effects of DDE, PCB, and chlordane on the binding of progesterone to its cytoplasmic receptor in the eggshell gland mucosa of birds and the endometrium of mammalian uterus. Comp. Biochem. Physiol. C. Pharmacol. Toxicol. Endocrinol. 89, 361368.[ISI]
Lundkvist, U., Kindahl, H., and Madej, A. (1987). Urinary levels of estrone sulfate and 11-ketotetranor prostaglandin F metabolite in pregnant guinea pigs given Clophen A50 (polychlorinated biphenyls). Biol. Reprod. 36, 109116.[Abstract]
Lutz, R. J., Dedrick, R. L., Matthews, H. B., Eling, T. E., and Anderson, M. W. (1977). A preliminary pharmacokinetic model for several chlorinated biphenyls in the rat. Drug Metab. Dispos. 5, 386396.[Abstract]
Masuda, Y., Kagawa, R., Tokudome, S., and Kuratsune, M. (1979). Transfer of polychlorinated biphenyls to the foetuses and offspring of mice. Food Cosmet. Toxicol. 16, 623627.
McEwen, B. S. (1994). Steroid hormone effects on brain: Novel insights connecting cellular and molecular features of brain cells to behavior. Meth. Neurosci. 22, 525542.
Messeri, M. D., Bickmeyer, U., Weinsberg, F., and Wiegand, H. (1997). Congener specific effects by polychlorinated biphenyls on catecholamine content and release in chromaffin cells. Arch. Toxicol. 71, 416421.[ISI][Medline]
Miller, S. C., Halloran, B. P., and DeLuca, H. F. (1982). Role of vitamin D in maternal skeletal changes during pregnancy and lactation: A histomorphometric study. Calcif. Tissue Int. 34, 245252.[ISI][Medline]
Miller, S. C., Halloran, B. P., DeLuca, H. F., and Jee, W. S. (1983). Studies on the role of vitamin D in early skeletal development, mineralization, and growth in rats. Calcif. Tissue Int. 33, 455460.
Moncrieff, M., and Fadahunsi, T. O. (1974). Congenital rickets due to maternal vitamin D deficiency. Arch. Dis. Child. 49, 810811.[ISI][Medline]
Montesissa, C., Di Lauro, F., Fadini, L., and Pompa, G. (1992). Elimination of PCB congeners via milk in rabbits administered Fenclor 64. Pharmacol. Toxicol. 71, 139143.[ISI][Medline]
Morales, N. M., Tuey, D. B., Colburn, W. A., and Matthews, H. B. (1979). Pharmacokinetics of multiple oral doses of selected polychlorinated biphenyls in mice. Toxicol. Appl. Pharmacol. 48, 397407.[ISI][Medline]
Namgung, R., Tsang, R. C., Specker, B. L., Sierra, R. I., and Ho, M. L. (1993). Reduced serum osteocalcin and 1,25-dihydroxyvitamin D concentrations and low bone mineral content in small for gestation age infants: Evidence of decreased bone formation rates. J. Pediatr. 112, 269275.
Nesaretnam, K., Corcoran, D., Dils, R. R., and Darbre, P. (1996). 3,4,3`,4`-Tetrachlorobiphenyl acts as an estrogen in vitro and in vivo. Mol. Endocrinol. 10, 923936.[Abstract]
Noren, K., and Lunden, A. (1991). Trend studies of polychlorinated biphenyls, dibenzo-p-dioxins and dibenzofurans in human milk. Chemosphere 23, 18951901.[ISI]
Norman, A. W. (1997). Rapid biological responses mediated by 1,25-dihydroxyvitamin D3: A case study of transcaltachia (rapid stimulation of intestinal calcium transport). In Vitamin D (D. Feldman, F. H. Glorieux, and J. W. Pike, Eds.), pp. 233256. Academic Press, San Diego.
Patnode, K. A., and Curtis, L. R. (1994). 2,2`,4,4`,5,5`and 3,3`,4,4`,5,5`-hexachlorobiphenyl alteration of uterine progesterone and estrogen receptors coincides with embryotoxicity in mink (Mustela vison). Toxicol. Appl. Pharmacol. 127, 918.[ISI][Medline]
Paulson, S. K., Ford, K. K., and Langman, C. B. (1990). Pregnancy does not alter the metabolic clearance of 1,25-dihydroxyvitamin D in rats. Am. J. Physiol. 258, E158E162.
Peterson, R. E., Theobald, H. M., and Kimmel, G. L. (1993). Developmental and reproductive toxicity of dioxins and related compounds: Cross-species comparisons. Crit. Rev. Toxicol. 23, 283335.[ISI][Medline]
Porterfield, S. P., and Hendrich, C. E. (1993). The role of thyroid hormones in prenatal and neonatal neurological development: Current perspectives. Endocr. Rev. 14, 94106.[ISI][Medline]
Ramamoorthy, K., Vyhlidal, C., Wang, F., Chen, I., Safe, S., McDonnell, D. P., Leonard, L. S., and Gaido, K. W. (1997). Additive estrogenic activities of a binary mixture of 2`,4`,6`-trichloroand 2`,3`,4`,5`-tetrachloro-4-biphenylol. Toxicol. Appl. Pharmacol. 147, 93100.[ISI][Medline]
Rodda, C. P., Kubota, M., Heath, J. A., Ebeling, P. R., Moseley, J. M., Care, A. D., Caple, I. W., and Martin, T. J. (1988). Evidence for a novel parathyroid hormone-related protein in fetal lamb parathyroid glands and sheep placenta: Comparisons with a similar protein implicated in humoral hypercalcaemia of malignancy. J. Endocrinol. 117, 261271.[Abstract]
Rogan, W. J., Gladen, B. C., McKinney, J. D., Carreras, N., Hardy, P., Thullen, J., Tinglestad, J., and Tully, M. (1986). Neonatal effects of transplacental exposure to PCBs and DDE. J. Pediatr. 109, 335341.[ISI][Medline]
Ross, R., and Dorsey, J. (1991). Postnatal changes in plasma 1,25-dihydroxyvitamin D3 in sheep: Role of altered clearance. Am. J. Physiol. 261, E635E641.
Ross, R., Dorsey, J. and Ellis, K. (1990). Progressive increases in 1,25-dihydroxyvitamin D3 production rate in multiple ovine pregnancies are independent of changes in the metabolic clearance rate. Pediatr. Res. 27, 192A.
Safe, S. (1990). Polychlorinated biphenyls (PCBs), dibenzo-p-dioxins (PCDDs), dibenzufurans (PCDFs), and related compounds: Environmental and mechanistic considerations which support the development of toxic equivalency factors (TEFs). Crit. Rev. Toxicol. 21, 5188.[ISI][Medline]
Safe, S. H. (1994). Polychlorinated biphenyls (PCBs): Environmental impact, biochemical and toxic responses, and implications for risk assessment. Crit. Rev. Toxicol. 24, 87149.[ISI][Medline]
Safe, S. H. (1995). Modulation of gene expression and endocrine response pathways by 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds. Pharmacol. Ther. 67, 247281.[ISI][Medline]
Safe, S., Safe, L., and Mullin, M. (1985). Polychlorinated biphenyls: Congener-specific analysis of a commercial mixture and a human milk extract. J. Agric. Food Chem. 33, 2429.[ISI]
Schantz, S. L. (1996). Developmental neurotoxicity of PCBs in humans: What do we know and where do we go from here? Neurotoxicol. Teratol. 18, 217227.[ISI][Medline]
Schulte, E., and Malisch, R. (1984). Calculation of the real PCB content in environmental samples. II. Gas chromatographic determination of the PCB concentration in human milk and butter. Fresenius Z. Anal. Chem. 314, 5459.
Siegel, S. (1956). Nonparametric statistics for the behavioral sciences. McGraw-Hill, New York.
Slater, S. J., Kelly, M. B., Taddeo, F. J., Larkin, J. D., Yeager, M. D., McLane, J. A., Ho, C., and Stubbs, C. D. (1995). Direct activation of protein kinase C by 1,25-dihydoxyvitamin D3. J. Biol. Chem. 270, 66396643.
Stellman, S. D., Djordjevic, M. V., Muscat, J. E., Gong, L., Bernstein, D., Citron, M. L., White, A., Kemeny, M., Busch, E., and Nafziger, A. N. (1998). Relative abundance of organochlorine pesticides and polychlorinated biphenyls in adipose tissue and serum of women in Long Island, New York. Cancer Epidemiol. Biomarkers Prev. 7, 489496.[Abstract]
Suarez, F., Rossignol, C., and Garabedian, M. (1998). Interactive effect of estradiol and vitamin D receptor gene polymorphisms as a possible determinant of growth in male and female infants. J. Clin. Endocrinol. Metab. 83, 35633568.
Takagi, Y., Aburada, S., Hashimoto, K., and Kitaura, T. (1986). Transfer and distribution of accumulated (14C)polychlorinated biphenyls from maternal to fetal and suckling rats. Arch. Environ. Contam. Toxicol. 15, 709715.[ISI][Medline]
Takeuchi, A., Okano, T., Sekimoto, H., and Kobayashi, T. (1994). The enzymatic formation of 1,25-dihydroxyvitamin D3 from 25-dihydroxyvitamin D3 in the liver of fetal rats. Comp. Biochem. Physiol. C. Pharmacol. Toxicol. Endocrinol. 109, 17.[ISI][Medline]
Tanaka, Y., Halloran, B., Schnoes, H. K., and DeLuca, H. F. (1979). In vitro production of 1,25-dihydroxyvitamin D3 by rat placental tissue. Proc. Natl. Acad. Sci. U.S.A. 76, 50335035.[Abstract]
Tryphonas, H., Hayward, S., O'Grady, L., Loo, J. C., Arnold, D. L., Bryce, F., and Zawidka, Z. Z. (1989). Immunotoxicity studies of PCB (Aroclor 1254) in the adult rhesus (Macaca mulatta) monkeypreliminary report. Int. J. Immunopharmacol. 11, 199206.[ISI][Medline]
Vanden Bossche, H. (1992). Inhibitors of P450-dependent steroid biosynthesis: From research to medical treatment. J. Steroid Biochem. Molec. Biol. 43, 10031021.[ISI]
Vodicnik, M. J. (1986). The effect of pregnancy and lactation on the disposition of (2,4,2`,4`-14C)-tetrachlorobiphenyl in the mouse. Fundam. Appl. Toxicol. 6, 5361.[ISI][Medline]
Vos, J. G., and Beems, R. B. (1971). Dermal toxicity studies of technical polychlorinated biphenyls and fractions thereof in rabbits. Toxicol. Appl. Pharmacol. 19, 617633.[ISI][Medline]
Walters, M. R. (1997). Other vitamin-D target tissues: Vitamin D actions in cardiovascular tissue and muscle, endocrine and reproductive tissues, and liver and lung. In Vitamin D (D. Feldman, F. H. Glorieux, and J. W. Pike, Eds.), pp. 463482. Academic Press, San Diego.
Wong, P. W., and Pessah, I. N. (1996). Ortho-substituted polychlorinated biphenyls alter calcium regulation by a ryanodine receptor-mediated mechanism: Structural specificity toward skeletal and cardiac-type microsomal calcium release channels. Mol. Pharmacol. 49, 740751.[Abstract]
Wong, P. W., and Pessah, I. N. (1997). Noncoplanar PCB 95 alters microsomal calcium transport by an immunophilin FKBP12-dependent mechanism. Mol. Pharmacol. 51, 693702.
Yeowell, H. N., Waxman, D. J., LeBlanc, G. A., Linko, P., and Goldstein, J. A. (1988). Induction of rat cytochrome P-450 3 and its mRNA by 3,4,5,3`,4`,5`-pentachlorobiphenyl. Mol. Pharmacol. 33, 272278.[Abstract]
Yeowell, H. N., Waxman, D. J., Wadhera, A., and Goldstein, J. A. (1987). Suppression of the constitutive, male-specific rat hepatic cytochrome P-450 2c and its mRNA by 3,4,5,3`,4`,5`-hexachlorobiphenyl and 3-methylcholanthrene. Mol. Pharmacol. 32, 340347.[Abstract]
Yoshizawa, T., Handa, Y., Uematsu, Y., Takeda, S., Sekine, K., Yoshihara, Y., Kawakami, T., Arioka, K., Sato, H., Uchiyama, Y., Masushige, S., Fukamizu, A., Matsumoto, T., and Kato, S. (1997). Mice lacking the vitamin D receptor exhibit impaired bone formation, uterine hypoplasia, and growth retardation after weaning. Nat. Genet. 16, 391396.[ISI][Medline]