* Huntingdon Life Sciences, Inc., East Millstone, New Jersey 08875;
MPI, Mattawan, Michigan 49071;
CONDEA Vista Company, Houston, Texas 77079;
The Dow Chemical Company, Midland, Michigan 48674; and
¶ American Chemistry Council, 1300 Wilson Boulevard, Arlington, Virginia 22209
Received January 23, 2001; accepted March 11, 2002
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ABSTRACT |
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Key Words: vinyl chloride; embryo-fetal; developmental; reproduction; two-generation; rat; Sprague-Dawley.
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INTRODUCTION |
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While chronic occupational VC exposure has been shown to produce hepatotoxicity, the effects of this exposure on parental reproductive function and on the developing human fetus have not been clearly delineated. Several authors have attributed birth defects in children to the chronic occupational VC exposure of the mothers' husbands. Other birth defects have been attributed to women working in close proximity to polymerization facilities. However, these authors have been unable to demonstrate a positive correlation between VC exposure and birth defects. One epidemiological study on men linked occupational exposure to narcosis-producing concentrations of VC with a higher incidence of impotence (Suciu et al., 1975). Many epidemiological studies on fetal development and reproductive function have been criticized by others conducting similar studies. They state that inappropriate methods and improper statistical analysis have made it difficult to positively correlate parental exposure with changes in reproductive performance and fetal development. Thus, the potential effects of VC exposure on the human reproductive system remain uncertain.
Animals exposed to VC exhibit toxicity in numerous organs including the liver, kidneys, endocrine, dermal, ocular, immune, and reproductive systems. The liver is the most prominent organ system affected in the animal studies, and the results correspond to human case reports (ATSDR, 1997). Hepatotoxicity in rats from VC exposure included hepatocellular degeneration (Sokal et al., 1980
; Torkelson et al., 1961
), hypertrophy (Wisniewska-Knypl et al., 1980
), changes in metabolic activity (Du et al., 1979
; Wisniewska-Knypl et al., 1980
), and an increase in the liver:body weight ratio (Torkelson et al., 1961
; Sokal et al., 1980
).
Research on the epidemiology of VC exposure on human fetal development and reproductive performance has been criticized for the lack of correlation between parental exposure and toxicity. Yet, animal studies have revealed potential targets within the reproductive system that could account for the reports of toxicity in humans. Few embryo-fetal/developmental toxicity studies are available in the literature. The most comprehensive study was reported by John et al. (1977, 1981). The strength of these studies is that they utilized multiple species (mice, rats, and rabbits), and investigated the embryo-fetal/developmental effects at comparable VC exposure levels. Results from these studies indicate that mice appeared to be more sensitive to VC toxicity than rats or rabbits. Mice exposed to 500 ppm VC showed maternal toxicity evidenced by decreases in body weight, and an increase in mortality. Because of the maternal toxicity associated with 500 ppm VC, there was a decrease in the litter size. There were also fetal toxicities including decreases in fetal weight and delayed ossification of skull bones. In rats exposed to 500 ppm VC, the only observed sign of maternal toxicity was a decrease in body weight gains compared to the control. In rabbits exposed to 500 ppm VC, the only observed sign of maternal toxicity was a decrease in feed consumption.
While there are a couple of embryo-fetal/developmental toxicity studies available in the literature, there are no published studies available within the literature in which the effect of VC exposure on the reproductive performance of parental animals has been investigated. There are dominant lethal studies in mice and chronic toxicity studies in rats that have examined the effect of VC on the male reproductive system. The results of the dominant lethal study in mice were negative when the mice were exposed to 5000 ppm for 4 h/day for 10 weeks (Himeno et al., 1983). Chronic toxicity studies with VC in rats have shown that chronic VC exposure produces damage to the seminiferous tubules, depletion of spermatocytes, damage to the spermatogenic epithelium, and disorders of spermatogenesis that lead to a decrease in testicular weight (Bi et al., 1985
; Sokal et al., 1980
). While the dominant lethal study in mice does not support effects of VC on the male reproductive system, the chronic rat study indicates that the male reproductive system may be a target of VC. Caveats to the effect of VC on the male reproductive system are that the researchers in the chronic toxicity rat study did not investigate whether these effects led to impotency and/or the inability of the male rats to sire offspring, nor did they investigate whether the observed effects of VC were reversible after VC exposure was terminated.
In an attempt to clarify the effect of VC exposure on the developing fetus and on reproductive performance, the current study was designed to provide a more comprehensive embryo-fetal/developmental and reproductive assessment of VC using current regulatory guidelines. The study was designed to assess maternal and/or embryo-fetal developmental and two-generation reproductive toxicity in rats that had been exposed to the same VC levels so that a more direct comparison of the study results would be possible.
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MATERIALS AND METHODS |
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Measurements of airborne concentrations of VC were made using a MIRAN® Ambient Air analyzer equipped with a strip chart recorder. Test atmosphere samples were taken hourly during the exposure periods. The exposure levels were determined by comparison of the measured absorbance to a calibrated response curve.
Embryo-fetal/developmental study.
This embryo-fetal/developmental study was conducted in accordance with the U.S. Environmental Protection Agency TSCA Test Guidelines (U.S. EPA, 1985), Organization for Economic Co-operation and Development (OECD) Guidelines for testing of chemicals, Section 4, Health Effects (OECD, 1981
), and European Economic Community (EEC) Methods for the determination of toxicity (EEC, 1988
). See Figure 1A
for schematic of the experimental design. Briefly, 100 nulliparous female CD® Sprague-Dawley Crl: CD® BR rats (25/group), 57 days of age and weighing 172252 g, were received from Charles River Laboratories (Portage, MI). Female rats were acclimated for approximately 2 weeks and then cohabitated (1:1) nightly with male CD® Sprague Dawley Crl: CD® BR rats from an in-house breeding colony (Huntingdon Life Sciences, East Millstone, NJ). Female rats were considered pregnant if the vaginal smear performed each morning following cohabitation contained sperm or if a vaginal plug was present. GD 0 was defined as the day on which evidence of mating was observed. On GD 0, each mated female rat was assigned to an exposure group using a computer randomization program that randomly assigned animals to most nearly equalize GD 0 body weights between groups. Female rats were exposed to VC daily from GD 6 through 19 (see Vinyl Chloride Exposure section for further details).
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All animals were observed twice daily for mortality and toxicological effects. Detailed physical examinations were performed on GD 0 and GD 6 through 20. Body weight and feed consumption values were recorded on GD 0, 6, 9, 12, 15, and 20. Postexposure observations were performed approximately a half hour after exposure. On GD 20, all female rats were euthanized via carbon dioxide inhalation, and a cesarean section and a macroscopic postmortem examination were performed on each. During the macroscopic postmortem examination, gravid uterus (with ovaries attached), kidneys, and liver weights were recorded. Uterine implantation data including the position and number of live and dead fetuses, early and late resorptions, implantation sites, and the number of corpora lutea were recorded. Fetuses were removed from the uterus, weighed, their gender was determined, and they were examined for external malformations. Approximately half of the fetuses from each litter were processed for soft tissue (visceral) evaluations using a micro-dissection procedure (Staples, 1974), and half of the fetuses from each litter were processed for skeletal and ossification evaluations after evisceration and staining with Alizarin Red S. Uteri without grossly visible implantation sites were stained according to the procedure of Salewski (1964) to identify the presence of early resorption sites. If no stained implantation sites were present, the rat was considered not pregnant.
Reproduction study.
This reproduction study was conducted in accordance with the U.S. Environmental Protection Agency TSCA Test Guidelines (U.S. EPA, 1985), Organization for Economic Cooperation and Development (OECD) Guidelines for testing of chemicals, Section 4, Health Effects (OECD, 1981
), and European Economic Community (EEC) Methods for the determination of toxicity (EEC, 1988
). See Figure 1B
for schematic of the experimental design.
F0 generation.
One hundred twenty male and 120 nulliparous female CD® Sprague-Dawley Crl: CD® BR rats (30/sex/group) were received from Charles River Laboratories (Portage, MI). The male and female rats were approximately 4 weeks of age at receipt. Both the male and female rats were acclimated for approximately 2 weeks prior to exposure to VC. Body weights for the male and female rats were 207273 and 137177 g, respectively. The F0 male and female rats were assigned to the exposure groups using a computerized randomization program, which randomly assigned animals to most nearly equalize body weights between groups. The F0 generation male and female rats were exposed to VC for a 10-week premating period and a 3-week mating period. The F0 generation male rats continued exposure through the postmating period. Female rats were exposed during gestation through GD 20. After GD 20, exposure to VC for the female rats was discontinued to allow delivery of litters, resumed on LD 4, and continued throughout the remainder of lactation. Unmated female rats continued exposure to VC until euthanized (see Vinyl Chloride exposure section for further details.)
During nonexposure periods, all animals were housed individually in suspended stainless steel cages with wire mesh floors, except during mating. The animal rooms were maintained on a 12-h light/dark cycle with temperature and humidity kept within the specified ranges (2024°C and 4070%, respectively).The female rats, beginning on GD 20 and continuing throughout lactation, were individually housed in plastic shoebox cages containing certified hardwood shavings (Lab Aspen Shavings, North Eastern Products Corporation, Warrenburg, NY). All animals were provided Certified Rodent Diet No. 5002 (meal) supplied by PMI Feeds, Inc. (St. Louis, MO) and water via an automated water system ad libitum.
Estrous cycle determination via a vaginal smear procedure were performed on the first 15 F0 generation female rats per group for the 3-week period prior to mating and continued until mating was confirmed. During the mating period, 1 male rat was cohoused with 1 female rat from the same exposure group nightly until evidence of mating was observed or for 14 consecutive days. Female rats were considered mated if the vaginal smear performed each morning following cohabitation contained sperm or if a vaginal plug was present. GD 0 was defined as the day on which evidence of mating was observed. Due to poor mating performance (primarily in the control group), unmated female rats in all groups were randomly assigned to a male rat known to inseminate another female rat from the same exposure group for an additional 6 days. Once mated, the female rats were removed from the mating unit and housed individually for the remainder of gestation.
All F0 generation animals were observed twice daily for mortality and toxicity. Detailed physical examinations were performed and body weight and feed consumption recorded weekly during the premating period for the male and female rats and during the postmating period for the male and unmated female rats. For mated female rats, body weights and feed consumption were recorded on GD 0, 7, 14, and 20 and LD 0, 4, 7, 10, 14, and 25. F1 litters were examined for the presence of live and dead pups as soon as possible after delivery on LD 0 until weaning on LD 25. On LD 4, litters were culled to 8 pups/litter with equal gender number/litter, where possible.
F0 generation rats were euthanized via carbon dioxide inhalation. The male rats were euthanized after parturition completion and the female rats were euthanized on day 2 of diestrus after weaning, assessed by daily vaginal smears, whenever possible. Female rats with no estrous cyclicity or irregular estrous cycling, as determined by vaginal smears, were euthanized as a group after the confirmed diestrous female rats had been euthanized. All parental animals were given a macroscopic postmortem examination. Reproductive tissues from the male rats (testes, left epididymis, prostate, seminal vesicles with coagulating glands and their fluids) and female rats (uterus and ovaries) were weighed and preserved in 10% neutral buffered formalin, except for the testes and epididymis, which were preserved in Bouin's fixative. In addition, the adrenal glands, brain, kidneys, liver, lungs, spleen, and thymus were weighed for all F0 male and female rats. Other tissues preserved in 10% neutral buffered formalin from the F0 generation parental animals were mammary glands, nasal tissues (turbinates), pituitary, and trachea. All preserved tissues were embedded in paraffin, sectioned on a microtome (47 µm thickness), mounted on glass slides, stained with hematoxylin and eosin, and examined by light microscopy for histopathological abnormalities. While staging of the seminiferous tubules was not conducted, the testes cross-sections were examined by a pathologist for potential qualitative histopathological changes.
F1 pups.
F1 pups had physical examinations performed, body weights recorded, and gender determinations performed on LD 0, 4, 7, 14, and 25. The F1 pups were weaned on postnatal day (PND) 25, at which time 2 pups/sex per litter were chosen at random to become the pool of animals from which the F1 generation was selected. Each litter contributed at least 1 pup/sex, when possible, for a total of 30 pups/sex/group. The F1 pups selected to become the F1 generation were housed in pairs, 2 littermates of the same sex/cage, in stainless steel cages with wire mesh floors until the last F1 litters weaned, after which, they were individually housed. All F1 weanlings selected for the F1 generation were assessed for postweaning developmental landmarks, vaginal patency and preputial separation, beginning on PND 28 and 40, respectively. At weaning, 15 male and female pups from each exposure level were selected for macroscopic and microscopic examinations. Pups were given a macroscopic postmortem examination following euthanasia via carbon dioxide inhalation. The reproductive organs (testes or ovaries), adrenal glands, brain, kidneys, liver, spleen, and thymus were weighed. All other pups, including those found dead, culled, or not selected for the F1 generation were given an external examination following euthanasia via carbon dioxide inhalation and if within normal limits, discarded.
F1 generation.
One hundred twenty male and 120 female rats (30/sex per group) selected from the F1 pups began daily exposure to VC on PND 26. The F1 generation male and female rats were exposed daily to VC for a 10-week premating period and a 3-week mating period. The F1 generation male rats continued exposure through the postmating period. Female rats were exposed during gestation through GD 20. After GD 20, exposure to VC for the female rats was discontinued to allow delivery of litters, resumed on LD 4 and continued throughout the remainder of lactation. Unmated female rats continued exposure to VC until euthanized. During nonexposure periods, all animals were housed, provided feed, water, and the animal room maintained the same as the F0 generation.
Estrous cycle determination via a vaginal smear procedure was performed on the first 15 F1 generation female rats per group for the 3-week period prior to mating and continued until mating was confirmed. During the mating period, 1 male rat was cohoused with 1 female rat from the same exposure group nightly until evidence of mating was observed or for 14 consecutive days. In the mating of the F1 generation, brother-sister pairings were avoided. Female rats were considered mated if the vaginal smear, performed each morning following cohabitation, contained sperm or if a vaginal plug was present. GD 0 was defined as the day on which evidence of mating was observed.
All F1 generation animals were observed twice daily for mortality and toxicological effects. Detailed physical examinations were performed and body weight and feed consumption recorded weekly during the premating period for the male and female rats and during the postmating period for the male and unmated female rats. For mated female rats, body weights and feed consumption were recorded on GD 0, 7, 14, and 20 and LD 0, 4, 7, 10, 14, and 21. F2 litters were examined for the presence of live and dead pups as soon as possible after delivery on LD 0 until weaning on LD 21. On LD 4, litters were culled to 8 pups/litter with equal gender number/litter, where possible.
F1 generation rats were euthanized via carbon dioxide inhalation. The male rats were euthanized after parturition completion and the female rats were euthanized on day 2 of diestrus, assessed by daily vaginal smears, whenever possible. Female rats with no estrous cyclicity or irregular estrous cycling, as determined by vaginal smears, were euthanized as a group after the confirmed diestrous female rats had been euthanized. All parental animals were given a macroscopic postmortem examination. Reproductive tissues from the male rats (testes, left epididymis, prostate, seminal vesicles with coagulating glands and their fluids) and female rats (uterus and ovaries) were weighed and preserved in 10% neutral buffered formalin, except for the testes and epididymis, which were preserved in Bouin's fixative. In addition, the adrenal glands, brain, kidneys, liver, lungs, spleen, and thymus were weighed for all F1 male and female rats. Other tissues preserved in 10% neutral buffered formalin from the F1 generation parental animals were mammary glands, nasal tissues (turbinates), pituitary, and trachea. All preserved tissues were embedded in paraffin, sectioned on a microtome (47 µm thickness), mounted on glass slides, stained with hematoxylin and eosin, and examined by light microscopy for histopathological abnormalities. While staging of the seminiferous tubules was not conducted, cross-sections of the testes were examined by a pathologist for potential qualitative histopathological changes.
F2 pups.
F2 pups had physical examinations performed, body weights recorded, and gender determinations performed on LD 0, 4, 7, 14, and 21. At weaning (PND 21), 15 male and female pups from each exposure level, from the F1 litters were selected for macroscopic and microscopic examinations. Pups were given a macroscopic postmortem examination following euthanasia via carbon dioxide inhalation. The reproductive organs (testes or ovaries), adrenal glands, brain, kidneys, liver, spleen, and thymus were weighed. All other pups, including those found dead, culled, or not selected for the F1 generation were given an external examination following euthanasia via carbon dioxide inhalation and if within normal limits, discarded.
Sperm analysis.
Sperm motility, caudal epididymal sperm count, and sperm morphology were assessed in 15 male rats per group from the F0 and F1 generation, including male rats that did not impregnate a female rat. Sperm evaluations were performed by Pathology Associates International (PAI) (Frederick, MD) using an automated Hamilton Thorne IVOS sperm analyzer. The male rats were euthanized via carbon dioxide inhalation followed by exsanguination. Following euthanasia, an incision in the abdominal cavity was made and the reproductive organs exposed. Sperm motility evaluations were conducted on semen collected from the right vas deferens. For the evaluations, the right vas deferens was dissected from the testes and immediately placed in a warmed solution of phosphate buffered saline containing 1% bovine serum albumin. After a 3-min "swimout" period was allowed, the sample was placed in the Hamilton Thorne IVOS automated sperm analyzer and 5 fields evaluated for percent motility for each animal. Total sperm count determinations were conducted on the right epididymis. For the sperm count evaluation, the right epididymis was dissected from the surrounding tissues and immediately frozen and shipped to PAI (Frederick, MD). The right epididymis was thawed and the caudal section trimmed, weighed, and mechanically homogenized. A sample of the homogenized epididymis was stained with disbenzimide (Hoescht, H33342) which uniquely stains the heads of the sperm and 20 fields evaluated by the automated sperm analyzer for each animal. The total number of sperm in the caudal epididymis was calculated and normalized based on the caudal epididymal weight. Sperm morphology was assessed from 2 samples prepared from the prehomogenized caudal epididymis following eosin staining. The 2 samples (minimum of 200 sperm cells/animal) were evaluated for head and tail morphological irregularities (Filler, 1993).
Mean and SD values for sperm motility, total count, and sperm morphology data were calculated and compared across groups using the Kruskal-Wallis nonparametric ANOVA test. If a significant effect occurred, the Wilcoxon (Mann-Whitney U) test was used for pairwise comparisons of each exposed group to the control group; p values less than 0.05 were considered statistically significant.
Statistical analyses.
As a result of different computerized data capture systems utilized during the embryo-fetal/developmental and reproductive toxicity studies, different standard statistical packages were used to assess the statistical significance of the experimental parameters. Maternal body weight and body weight gains during gestation and lactation, fetal and pup body weights, mean gestation length, number of corpora lutea, number of fetuses or pups, fetal body weight, early and late resorptions, and organ weights (embryo-fetal/developmental study) were statistically evaluated for equality of means using a one-way ANOVA, followed by a post hoc test, if needed (Dunlap et al., 1981). If ANOVA was significant, Dunnett's test was performed to determine which data differed from the control (Dunnett, 1955
, 1964
); p values less than 0.05 were considered statistically significant.
Premating, mating, and postmating body weight and body weight gains, feed consumption, organ weights (reproduction study), and mean age to vaginal patency and preputial separation were statistically evaluated for equal variance using Bartlett's test (Snedecor and Cochran, 1967). If variances were equal, the parametric procedures, a one-way ANOVA using the F distribution to assess significance was performed. If significant differences were indicated a Dunnett's test was used to determine which means were significantly different from the control (Dunnett, 1955
, 1964
). If variances were not equal, the nonparametric procedures, Kruskal-Wallis test followed by Dunn's summed rank test to determine which exposures differed from control was performed (Hollander and Wolfe, 1973
); p values less than 0.05 were considered statistically significant.
Mating indices, pregnancy rates, male rat fertility indices, pup survival indices, and mortality rates were statistically evaluated using a Fisher Exact Test with Bonferroni correction to identify differences in incidence data between groups (Dunlap and Duffy, 1975; Hollander and Wolfe, 1973
; Siegel, 1956
); p values less than 0.05 or 0.01 were considered statistically significant.
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RESULTS |
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Embryo-Fetal/Developmental Study
All animals, including the control, survived to scheduled euthanasia on GD 20 (data not shown). During GD 1520 and GD 620, VC exposure caused a slight, but statistically significant suppression in maternal body weight gains, at all exposure levels (Table 1). However, pregnancy rates, clinical observations, feed consumption, macroscopic postmortem findings (data not shown), uterine implantation data, fetal gender distribution and body weight, fetal malformations and variations remained comparable between the VC and control groups (Tables 25
). Maternal absolute and relative kidney and liver weights in the 10 ppm VC exposed groups were comparable to control (Table 6
). In the 100 and 1100 ppm groups, the absolute kidney and liver weights were comparable to the control. However, in the 100 ppm exposed group, the kidney relative to body weight ratio was statistically significantly increased, while in the 1100 ppm exposed group, the organ relative to body weight ratios for both the kidney and liver were statistically significantly increased.
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During the premating period for the F0 generation female rats, the control and VC exposure groups experienced 4 to 6 estrous intervals over the 22-day evaluation period (data not shown). The initial mating period for the F0 generation was 14 days during which the mating indices for the control and VC groups was 80 and 8797%, respectively. Because of the low mating index of the control group, the mating period for all groups was extended for 6 additional days for a total of 20 days of mating. The overall 20-day F0 generation female mating indices at the end of the mating period for the control, 10, 100, and 1100 ppm VC groups were 93, 97, 93, and 100%, respectively. Even though there was an initial decrease in the mating index for the control group in the F0 generation, overall female and male mating indices for the F0 generation were not significantly affected by VC exposure (Table 7). Pregnancy rates for the F0 generation were comparable between control and VC exposed groups (Table 7
).
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Body weight, body weight gains, and feed consumption during gestation and lactation for the F1 generation were comparable between the control and VC exposure groups (data not shown). The gestation index and duration of gestation were comparable between the control and VC exposure groups (Table 13). In the F2 litters, there was a statistically significant decrease in the mean number of pups delivered in the 1100 ppm exposed group (Table 13
). These differences in the mean number of pups delivered is not considered exposure-related since no dose response was observed, and while the values were lower than respective F1 control group values, they are comparable to the F0 control group values. Viability indices for the F2 pups exposed to 10, 100, and 1100 ppm VC were increased when compared to the control group. These increases were considered incidental and unrelated to VC exposure. Pup gender distribution and pup body weights were also unaffected by VC exposure in the F2 litters (data not shown).
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DISCUSSION |
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There was no embyro-fetal or developmental toxicity at any exposure levels as evidenced by the lack of malformations, variations, and significant effects on fetal body weight. John et al. (1977, 1981) also reported a lack of embryo-fetal/developmental toxicity in rats exposed to VC. They found comparable fetal body weight, external, visceral, and skeletal variations in control rats and those exposed to VC levels of 500 and 2500 ppm during GD 615. They also reported that mice appeared to be more sensitive to VC exposure than rats or rabbits. In our study, we exposed rats to levels of VC that were approximately 101100 times higher than permissible occupational exposure levels of 1 ppm. The embryo-fetal/developmental results indicate that exposure of VC up to 1100 times the permissible occupational exposure level via inhalation during pregnancy did not result in adverse developmental effects. These results may provide an explanation for the epidemiological researcher's inability to demonstrate a positive correlation between exposure and the development of birth defects in children born to women whose husbands were occupationally exposed to VC and/or to women within close proximity to polymerization facilities.
In the embryo-fetal developmental study, the observed effects of VC on maternal kidney and liver weight relative to body weight can be directly correlated with the amount of VC exposure. These tissues were not examined histopathologically, thus it is unknown what changes occurred that led to the significant increases in kidney weights. One study in mice noted that the kidney may be a target of VC exposure (Feron and Kroes, 1979). However, it should be noted that no human epidemiological studies have identified the kidney as a potential target organ. Hepatotoxicity is one result of prolonged exposure to VC.
The two-generation reproductive toxicity results indicate that VC exposures of up to 1100 ppm over multiple generations in rats did not affect body weight, feed consumption, ability to reproduce, gestation index or length, preweaning or postweaning developmental landmarks. Furthermore, the sperm analysis for either the F0 or F1 generation animals was unaffected by VC exposure. To our knowledge this is the first study that directly measured sperm counts, as well as sperm motility and head and tail morphology following VC exposure. This conflicts with an earlier study in which chronic VC exposure damaged the seminiferous tubules, depleted spermatocytes, and damaged spermatogenic epithelium, leading to a decrease in testicular weight (Bi et al., 1985; Sokal et al., 1980
). However, unlike our study, the rats were chronically exposed to narcosis producing concentrations significantly greater than 1000 ppm. Humans are very unlikely to be exposed to such high concentrations for even short periods of time.
In this study, the liver was the primary site of toxicity from VC exposure. In both the F0 and F1 generation, male and female rats exhibited changes in liver weights and/or histopathological alterations. Histopathological alterations consisted of centrilobular hypertrophy and acidophilic staining of hepatocytes in the F0 generation animals. F1 generation animals exhibited centrilobular hypertrophy and acidophilic, basophilic, or clear cell foci. Hepatotoxicity occurs by the actions of cytochrome P450 2E1 to metabolize VC into 2-chloroethylene oxide, which covalently binds to nucleic acids and proteins to produce genotoxicity (Easter and Von Burg, 1994). Ultimately, this leads to hepatic angiosarcoma. Centrilobular hypertrophy is a common compensatory reaction following toxic insult to the liver and was observed in all VC treated groups. However, it was more prevalent in the F0 and F1 generation male and female rats exposed to 100 and 1100 ppm. Others have similarly shown that subchronic/chronic VC exposure in rats can lead to hepatotoxicity, including hepatocellular degeneration (Sokal et al., 1980
; Torkelson et al., 1961
), hypertrophy (Wisniewska-Knypl et al., 1980
), and increases in the liver to body weight ratio (Sokal et al., 1980
; Torkelson et al., 1961
).
In summary, our results indicate that VC up to 1100 ppm exposure did not adversely affect embryo-fetal/developmental and/or reproductive capability over two generations in rats. However, the liver was affected as evidenced by increases in liver weight and/or histologically identified cellular alterations, such as centrilobular hypertrophy. Based on our results, the NOAEL for embryo-fetal/development is 1100 ppm, and the NOAEL for reproduction is 1100 ppm. We believe that this study provides a more systematic and comprehensive assessment of embryo-fetal/developmental and reproductive effects of chronic VC exposure than previous publications. It is hoped that these results will be incorporated into future risk assessments examining occupational exposure to VC.
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NOTES |
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