1 Institute of Obstetrics and Gynaecology of Modena, via del Pozzo 71, 41100 Modena and 2 Institute of Obstetrics and Gynaecology of Cagliari, via Ospedale 46, 09124 Cagliari, Italy
![]() |
Abstract |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key words: C-peptide/GnRHa/insulin/ovary/PCOS
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
Materials and methods
Each woman gave written informed consent to the study which was previously approved by our local ethical committee. Eight lean [body mass index (BMI) = 22.8 ± 0.25] women, 25.1 ± 1.8 years of age, suffering from PCOS and six age- (24.8 ± 1.7 years of age) and weight- (BMI = 22.5 ± 0.18) matched non-hyperandrogenic women with normal ovarian function and symptomatic uterine leiomyomata or endometriosis were enrolled. PCOS was defined as persistent amenorrhoea or oligomenorrhoea of perimenarchal onset, with three or more of these features: ratio luteinizing hormone (LH)/follicle stimulating hormone (FSH) >1.5, ovarian hyperandrogenism as defined by high levels of total testosterone, free testosterone or androstenedione, Ferriman and Gallwey hirsutism score >10, ultrasound evidence of PCOS (Paoletti et al., 1995). Each woman was instructed to consume >200 g/day carbohydrate in the 3 days before testing. Following an overnight fast of 12 h, each woman was admitted to the hospital at 0700 h on 2 consecutive days. Glucose metabolism was investigated by both an oral glucose tolerance test (OGTT) and the minimal model method approach, based on analysis of a frequently sampled i.v. glucose tolerance test (FSIGT) (Welch et al., 1990
) performed on 2 consecutive days in a randomized order.
For the OGTT, a polyethylene catheter inserted in an antecubital vein was kept patent by a slow infusion of saline solution. A glucose load of 75 g was given orally at 0900 h. Samples of arterialized blood (i.e. venous blood with glucose content similar to that of arterial blood), obtained by forearm warming, were collected at times 30, 0, 15, 30, 60, 90, 120 and 180 min after glucose administration.
For the FSIGT, two polyethylene catheters placed in two antecubital veins were kept patent by a slow infusion of saline solution. One catheter was used for i.v. glucose or insulin administration and the other one for blood collection. At 0900 h, glucose (0.3 g/kg) was injected over 1 min i.v. and was followed 20 min later by an i.v. insulin bolus (Actrapid H-M; Novo Nordisk, SpA, Rome, Italy; 0.03 IU/kg). Samples of arterialized blood were collected at time 15, 10, 5, 1, 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 14, 16, 20, 22, 23, 24, 25, 27, 30, 40, 60, 70, 80, 90, 100, 120, 160 and 180 min after glucose load.
Each woman was assigned to receive every 28 days for three cycles a s.c. implant of goserelin depot (3.6 mg Zoladex; Zeneca, Milan, Italy), and at the end of treatment was submitted to the same investigations.
Blood samples, collected on ice into heparinized glass tubes, were immediately centrifuged at 1500 g for 15 min. An aliquot of plasma was immediately tested for glucose levels, while another aliquot was immediately frozen to 25°C until assayed. As in previous studies (Cagnacci et al., 1998), blood glucose was assayed by an autoanalyser using the glucose oxidase colorimetric method. Insulin levels were assayed in duplicate in all samples by a radioimmunoassay method using commercial kits (Biodata; Guidonia Montecelio, Roma, Italy), with intra- and inter-assay coefficients of variation (CV) of 6.2 and 7% respectively, and sensitivity of 14.35 pmol/l. C-Peptide levels were analysed in duplicate in all OGTT samples, and in the samples collected in the first 20 min of FSIGT by commercial radioimmunoassay kits (Biodata) with intra- and inter-assay coefficients of variation of 3.2 and 8.5% respectively, and sensitivity of 33.1 pmol/l (Cagnacci et al., 1998
). Circulating levels of LH, FSH, prolactin, oestradiol, total testosterone, free testosterone, androstenedione and dehydroepiandrosterone sulphate (DHEAS) were also analysed in baseline samples by radioimmunoassay (Paoletti et al., 1995
).
Responses of glucose, insulin and C-peptide observed during OGTT and in the first 20 min of FSIGT, were reported as absolute values and as area under the curve, calculated by the trapezoid method and expressed in arbitrary units (nmol/l or pmol/lxmin; AUC). In order to have an index of hepatic insulin clearance, the C-peptide/insulin ratio of absolute and integrated values was also calculated (Cagnacci et al., 1992, 1998
). Glucose and insulin values obtained during FSIGT were used to calculate by a computerized algorithm (MINMOD) the sensitivity of glucose elimination to insulin (Si) that is inversely related to insulin resistance. Si is defined as the increase in fractional glucose disappearance due to an increment in plasma insulin, i.e. insulin action (independent of both glucose and insulin levels). Si from minimal model approaches is comparable to values from clamp techniques (Beard et al., 1986
; Bergman et al., 1987
). Glucose-dependent glucose elimination (Sg) was defined as the total effect of glucose on fractional glucose disappearance independent of an increase in insulin, but including the contribution of basal insulin (Welch et al., 1990
). Si was expressed in unitsx104/minxµ/ml, and Sg in unitsx104/min.
Statistical analysis of the results was performed by the t-test for paired data, or Wilcoxon test, as specified. Two-way analysis of variance (ANOVA) for repeated measures (treatmentxtime, with subjects as replicates) was also used to evaluate differences on glucose or hormone responses to OGTT or first 20 min of FSIGT. All the results are expressed as the mean ± standard error (SE).
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
|
|
|
In comparison to the control group, women with PCOS showed higher levels (P < 0.05) of insulin and C-peptide in fasting conditions, a higher C-peptide/insulin ratio at the OGTT (P < 0.05), and a lower C-peptide/insulin ratio at the FSIGT (P < 0.02). Sg was lower in women with PCOS (P < 0.05). Also, Si was lower in women with PCOS prior to treatment (P < 0.01), but not during treatment.
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
In women with PCOS, a simple evaluation of glucoseinsulin metabolism via an OGTT failed to show both herein and previously (Geffner et al., 1986; Gardir et al., 1990; Lanzone et al., 1990
; Dale et al., 1992), a relevant modification of glucose metabolism during the suppression of ovarian activity. However, by using the minimal model method, it was observed that the reduced Si of lean PCOS was almost completely abolished by suppression of ovarian function via the prolonged administration of a GnRHa. These results are in accordance with recent data (Moghetti et al., 1996
; Dahlgren et al., 1998
) in which insulin sensitivity was evaluated by the hyperinsulinaemic glucose clamp technique, in a population of women with normal to moderately increased BMI, and are at variance with those of Dunaif et al. (1990) obtained with an incomplete pituitary desensitization in overweight to frankly obese PCOS.
A reduction of Si does not seem to be the only abnormality of glucose metabolism present in the lean women with PCOS in this study, and, in accordance with what has previously been found in overweight women with PCOS, a reduction in Sg was also present (Falcone et al., 1992). In support of its different and independent regulation (Falcone et al., 1992
) Sg, in contrast to Si, was not modified by ovarian suppression. Because alterations of glucose dependent glucose transport have not been observed in in-vitro cells of women with PCOS (Ciaraldi et al., 1992), the mechanisms implicated in Sg alteration are unclear. However, a decrease in Sg may favour enhanced insulin secretion from pancreatic ß-cells (Holte et al., 1994
; Ciampelli et al., 1998
) and contribute to generate or perpetuate hyperinsulinaemia and peripheral insulin resistance of PCOS (Dunaif, 1997
; Nestler and Jakubowicz, 1997
; Sattar et al., 1998
).
Hepatic insulin clearance, roughly evaluated by the integrated C-peptide/insulin ratio during i.v. glucose administration, was lower in PCOS than in controls. This alteration was not likely to be dependent on hyperandrogenism, which does not seem to influence hepatic insulin sensitivity (Peiris et al., 1989; Dunaif et al., 1990
; Moghetti et al., 1996
), and indeed hepatic insulin clearance was not modified by ovarian suppression. On the other hand, when the C-peptide/insulin ratio was evaluated during OGTT, it was not reduced and indeed was enhanced in women with PCOS. Because oral glucose administration stimulates gastrointestinal factors, such as incretins (Shapiro et al., 1987
), capable of influencing hepatic insulin clearance (Shuster et al., 1988
), it is likely that this stimulus is modified in women with PCOS. Indeed, some gastrointestinal mechanisms involved in glucose metabolism are sensitive to sex steroids (Cagnacci et al., 1998
). Additionally, in PCOS fasting beta-endorphin levels are elevated (Givens et al., 1987
) and are further stimulated by oral glucose administration (Laaitikainen et al., 1989; Carmina et al., 1992
). Because beta-endorphin is believed to influence glucoseinsulin metabolism (Givens et al., 1987
; Fulghesu et al., 1995
), its modifications may also play a role in the complex modulation of hepatic insulin clearance of PCOS.
A surprising finding of the present study was the failure of the marked ovarian suppression induced by the GnRHa to modify glucose metabolism of non-hyperandrogenic women. This seems at variance with data suggesting that hypo-oestrogenism may impair glucose metabolism in postmenopausal women (Cagnacci et al., 1992, 1998
; Elkind-Hirsch et al., 1993
; Godsland et al., 1993
; Lindheim et al., 1993
). However, in postmenopausal women, as the consequence of ageing (Gumbiner et al., 1989
; Shimokata et al., 1991
), glucose metabolism may be more critically regulated, and modifications of gonadal steroids may have a more dramatic impact than in young lean women. Furthermore, hypo-oestrogenism induced by the GnRHa administration is different from that of the menopause. GnRHa may exert direct effects on insulin clearance, which can mask eventual negative effects of hypo-oestrogenism (Dunaif et al., 1990
). Furthermore, the administration of GnRHa is associated with a marked decline in ovarian androgens, as well as with a reduction in growth hormone levels (Kaltsas et al., 1998
) which may counterbalance the negative effect of hypo-oestrogenism on glucose metabolism. Whatever the mechanism is, the present data indicate that at least in young lean women, the administration of GnRHa has no negative effect on glucose metabolism, and this is reassuring for the prolonged administration of these compounds.
![]() |
Notes |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
Bergman, R.N., Prager, R., Volund, A. and Olefsky J.M. (1987) Equivalence of the insulin sensitivity index in man derived by the minimal model method and the euglycemic clamp. J. Clin. Invest., 70, 790800.
Buyalos, R.P., Geffner, M.E., Azziz, R. and Judd, H.L. (1997) Impact of overnight dexamethasone suppression of the adrenal androgen response to an oral glucose tolerance test in women with and without polycystic ovary syndrome. Hum. Reprod., 12, 11381141.[ISI][Medline]
Cagnacci, A., Soldani, R., Carriero, P.L. et al. (1992) Effects of low doses of transdermal 17-ß-estradiol on carbohydrate metabolism in postmenopausal women. J. Clin. Endocrinol. Metab., 74, 13961400.[Abstract]
Cagnacci, A., Tuveri, F., Cirillo, R., et al. (1998) The effect of transdermal 17-ß-estradiol on glucose metabolism of postmenopausal women is evident during the oral but not the intravenous glucose administration. Maturitas, 28, 163167.[ISI]
Carmina, E., Ditkoff, E.C., Malizia, G. et al. (1992) Increased circulating levels of immunoreactive beta-endorphin in polycystic ovary syndrome is not caused by increased pituitary secretion. Am. J. Obstet. Gynecol., 167, 18191824.[ISI][Medline]
Ciampelli, M., Fulghesu, A.M., Murgia, F. et al. (1998) Acute insulin response to intravenous glucagon in polycystic ovary syndrome. Hum. Reprod., 13, 847851.[Abstract]
Ciaraldi, T.P., elRoeiy, A., Madar, Z. et al. (1992) Cellular mechanisms of insulin resistance in polycystic ovarian syndrome. J. Clin. Endocrinol. Metab., 75, 577583.[Abstract]
Cohen, J.C. and Hickman, R. (1987) Insulin resistance and diminished glucose tolerance in powerlifters ingesting anabolic steroids. J. Clin. Endocrinol. Metab., 64, 960963.[Abstract]
Dahlgren, E., Landin, K., Krotkiewski, M. et al. (1998) Effects of two antiandrogen treatments on hirsutism and insulin sensitivity in women with polycystic ovary syndrome. Hum. Reprod., 13, 27062711.
Dale, P.O., DJoseland, O., Jervell, J. et al. (1992) Persistence of hyperinsulinemia in polycystic ovary syndrome after ovarian suppression by gonadotropin-releasing hormone agonist. Acta Endocrinol., 126, 132136.[ISI][Medline]
Diamond, M.P., Simonson, D.C. and De Fronzo, R.A. (1989) Menstrual cyclicity has a profound effect on glucose homeostasis. Fertil. Steril., 52, 204208.[ISI][Medline]
Dunaif, A. (1997) Insulin resistance and the polycystic ovary syndrome: mechanisms and implications for pathogenesis. Endocr. Rev., 18, 774800.
Dunaif, A., Green, G., Futterweit, W. et al. (1990) Suppression of hyperandrogenism does not improve peripheral or hepatic insulin resistance in the polycystic ovary syndrome. J. Clin. Endocrinol. Metab., 70, 699704.[Abstract]
Dunaif, A., Segal, K.R., Shelley, D.R. et al. (1992) Evidence for distinctive and intrinsic defects in insulin action in polycystic ovary syndrome. Diabetes, 41, 12571266.[Abstract]
Elkind-Hirsch, K.E., Sherman, L.D. and Malinak R. (1993) Hormone replacement therapy alters insulin sensitivity in young women with premature ovarian failure. J. Clin. Endocrinol. Metab., 76, 472475.[Abstract]
Falcone, T., Little, A.B. and Morris, D. (1992) Impaired glucose effectiveness in patients with polycystic ovary syndrome. Hum. Reprod., 7, 922925.[Abstract]
Fulghesu, A.M., Ciampelli, M., Fortini, A. et al. (1995) Effect of opioid blockade on insulin metabolism on polycystic ovarian disease. Hum. Reprod., 10, 22532257.[Abstract]
Gadir, A.A., Khatim, M.S., Mowafi, R.S. et al. (1990) Hormonal changes in patients with polycystic ovarian disease after ovarian electrocautery or pituitary desensitization. Clin. Endocrinol. (Oxf.), 32, 749754.[ISI][Medline]
Geffner, M.E., Kaplan, S.A., Bersch, N. et al. (1986) Persistence of insulin resistance in polycystic ovarian disease after inhibition of ovarian steroid secretion. Fertil. Steril., 45, 327333.[ISI][Medline]
Givens, J.R., Kurtz, B.R., Kitabchi, A.E. et al. (1987) Reduction of hyperinsulinemia and insulin resistance by opiate receptor blockade in the polycystic ovary syndrome with acanthosis nigricans. J. Clin. Endocrinol. Metab., 64, 377382.[Abstract]
Godsland, I.F., Gangar, K., Walton, C. et al. (1993) Insulin resistance, secretion, and elimination in postmenopausal women receiving oral or transdermal hormone replacement therapy. Metabolism, 42, 846853.[ISI][Medline]
Gumbiner, B., Polonsky, K.S., Beltz, W.F. et al. (1989) Effects of aging on insulin secretion. Diabetes, 38, 15491556.[Abstract]
Holmang, A., Larsson, B.M., Brzezinska, M. et al. (1992) Effects of short-term testosterone exposure on insulin sensitivity of muscle in female rats. Am. J. Physiol., 262, E851E855.
Holte, J., Bergh, T., Berne, C. et al. (1994) Enhanced early insulin response to glucose in relation to insulin resistance in women with polycystic ovary syndrome and normal glucose tolerance. J. Clin. Endocrinol. Metab., 78, 10521058.[Abstract]
Kaltsas, T., Pontikides, N., Krassas, G.E. et al. (1998) Effect of gonadotrophin-releasing hormone agonist treatment on growth hormone secretion in women with polycystic ovarian syndrome. Hum. Reprod., 13, 2226.[Abstract]
Laatikainen, T.J., Tiitinen, A.E., Salminen-Lappalainen, K.R. et al. (1989) Response of plasma beta-endorphin and insulin to oral glucose tolerance test in non-obese women with polycystic ovaries. Gynecol. Endocrinol., 3, 241247.[ISI][Medline]
Lanzone, A., Fulghesu, A.M., Andreani, C.L. et al. (1990) Insulin secretion in polycystic ovarian disease: effect of ovarian suppression by GnRH agonist. Hum. Reprod., 5, 143149.[Abstract]
Lindheim, S.R., Presser, S.C., Ditkoff, E.C. et al. (1993) A possible bimodal effect of estrogen on insulin sensitivity in postmenopausal women and the attenuating effect of added progestin. Fertil. Steril., 60, 664667.[ISI][Medline]
Moghetti, P., Tosi, F., Castello, R. et al. (1996) The insulin resistance in women with hyperandrogenism is partially reversed by antiandrogen treatment: evidence that androgens impair insulin action in women. J. Clin. Endocrinol. Metab., 81, 952960.[Abstract]
Mortola, J.F., and Yen, S.S.C. (1990) The effects of oral dehydroepiandrosterone on endocrinemetabolic parameters in postmenopausal women. J. Clin. Endocrinol. Metab., 71, 696704.[Abstract]
Nestler, J.E. and Jakubowicz D.J. (1997) Decreases in ovarian cytochrome P450c17a activity and serum free testosterone after reduction of insulin secretion in polycystic ovary syndrome. N. Engl. J. Med., 335, 617623.
Paoletti, A.M., Cagnacci, A., Soldani, R. et al. (1995) Evidence that an altered prolactin release is consequent to abnormal ovarian activity in polycystic ovary syndrome. Fertil. Steril., 64, 10941098.[ISI][Medline]
Peiris, A.N., Aiman, E.J., Drucker, W.D. et al. (1989) The relative contributions of hepatic and peripheral tissues to insulin resistance in hyperandrogenic women. J. Clin. Endocrinol. Metab., 68, 715720.[Abstract]
Polderman, K.H., Gooren, L.J.G., Asscheman, H. et al. (1994) Induction of insulin resistance by estrogens and androgens. J. Clin. Endocrinol. Metab., 79, 265271.[Abstract]
Sattar, N., Hopkinson, Z.E.C. and Greer, I.A. (1998) Insulin-sensitizing agents and polycystic-ovary syndrome. Lancet, 351, 305307.[ISI][Medline]
Shapiro, E.T., Tillil, H., Miller, M.A. et al. (1987) Insulin secretion and clearance. Comparisons after oral and intravenous glucose. Diabetes, 36, 13651371.[Abstract]
Shimokata, H., Muller, D.C., Fleg, J.L. et al. (1991) Age as independent determinant of glucose tolerance. Diabetes, 40, 4451.[Abstract]
Shuster, L.T., Go, V.L.W., Rizza, R.A. et al. (1988) Incretin effect due to increased secretion and decreased clearance of insulin in normal humans. Diabetes, 37, 200203.[Abstract]
Vrtacnik-Bokal, E. and Meden-Vrtovec, H. (1998) Uteroovarian arterial blood flow and hormonal profile in patients with polycystic ovary syndrome. Hum. Reprod., 13, 815821.[Abstract]
Welch, S., Gebhart, S.S.P., Bergman, R.N. et al. (1990) Minimal model analysis of intravenous glucose tolerance test-derived insulin sensitivity in diabetics subjects. J. Clin. Endocrinol. Metab., 71, 15081518.[Abstract]
Submitted on May 22, 1998; accepted on December 16, 1998.