Insulin secretory responses to rising and falling glucose concentrations are delayed in subjects with impaired glucose tolerance.

AIMS/HYPOTHESIS: We hypothesized that beta-cell responses to changes in glucose would not be normal in subjects with impaired glucose tolerance (IGT). METHODS: Three groups of 6 subjects were studied: normal weight with normal glucose tolerance (control subjects); obese with normal glucose tolerance (Obese-NGT); and obese with IGT (Obese-IGT). All subjects had a graded glucose infusion protocol to increase (step-up) and then decrease (step-down) plasma glucose. We obtained average insulin-secretion rates (ISR) over the glucose range common to all three groups during step-up and step-down phases, minimal model indices of beta-cell function (f(b), f(d), f(s), T(up), T(down) ), and insulin sensitivity (Si). RESULTS: ISR differed significantly between step-up and -down phases only in Obese-IGT individuals. Basal (f(b)) and stimulated (f(d), f(s)) beta-cell sensitivity to glucose were similar in the three groups. Delays between glucose stimulus and beta-cell response during both step-up (T(up)) and -down (T(down)) phases were higher in Obese-IGT compared to Controls and Obese-NGT individuals. The product ISR x Si (10(-5.)min(-2) x l) was lower in Obese-IGT compared to Controls, both during step-up (919 +/- 851 vs 3192 +/- 1185, p < 0.05) and step-down (1455 +/- 1203 vs 3625 +/- 691, p < 0.05) phases. Consistently, the product f(s) x Si (10(-14.)min(-2). pmol(-1) x l) was lower in Obese-IGT than in control subjects (27.6 +/- 25.4 vs 103.1 +/- 20.2, p < 0.05). CONCLUSION/INTERPRETATION: Subjects with IGT are not able to secrete insulin to compensate adequately for insulin resistance. They also show delays in the timing of the beta-cell response to glucose when glucose levels are either rising or falling.

Heritability of insulin secretion and insulin action in women with polycystic ovary syndrome and their first degree relatives.

Polycystic ovary syndrome (PCOS), one of the most common endocrine disorders of reproductive age women, is associated with an increased risk of type 2 diabetes mellitus. Defects in both insulin action and insulin secretion contribute to this predisposition to diabetes, but the extent to which these defects are heritable among PCOS families has not been examined. In the present study we used the frequently sampled iv glucose tolerance test to quantitate insulin secretion (AIRg), insulin action (Si), and their product (AIRg x Si) among women with PCOS (n = 33) and their nondiabetic first degree relatives (n = 48). We then quantitated the heritability of these measures from familial correlations estimated within a genetic model. Familial (spousal, rhoMF; parent-offspring, rhoPO; and sibling, rhoSS) correlations were derived for log-transformed body mass index (BMI) as well as for AIRg, Si, and AIRg x Si, the latter three of which were adjusted for BMI. There was no evidence of significant heritability for either lnBMI or lnSi in these families. In contrast, the sibling correlation (rhoSS = 0.74) for lnAIRg was highly significant (chi(2) = 7.65; 1 df; P = 0.006). In addition, the parameter quantitating insulin secretion in relation to insulin sensitivity [i.e. ln(AIRg x Si)] was significant among siblings (rho(SS) = 0.74; chi(2) = 4.32; 1 df; P = 0.04). In summary, the results of the present study indicate that there is an heritable component to beta-cell dysfunction in families of women with PCOS. We conclude that heritability of beta-cell dysfunction is likely to be a significant factor in the predisposition to diabetes in PCOS.

Quantitative indexes of beta-cell function during graded up&down glucose infusion from C-peptide minimal models.

Availability of quantitative indexes of insulin secretion is important for definition of the alterations in beta-cell responsivity to glucose associated with different physiopathological states. This is presently possible by using the intravenous glucose tolerance test (IVGTT) in conjunction with the C-peptide minimal model. However, the secretory response to a more physiological slowly increasing/decreasing glucose stimulus may uncover novel features of beta-cell function. Therefore, plasma C-peptide and glucose data from a graded glucose infusion protocol (seven 40-min periods of 0, 4, 8, 16, 8, 4, and 0 mg. kg(-1). min(-1)) in eight normal subjects were analyzed by use of a new model of insulin secretion and kinetics. The model assumes a two-compartment description of C-peptide kinetics and describes the stimulatory effect on insulin secretion of both glucose concentration and the rate at which glucose increases. It provides in each individual the insulin secretion profile and three indexes of pancreatic sensitivity to glucose: Phi(s), Phi(d), and Phi(b), related, respectively, to the control of insulin secretion by the glucose level (static control), the rate at which glucose increases (dynamic control), and basal glucose. Indexes (means +/- SE) were Phi(s) = 18.8 +/- 1.8 (10(9) min(-1)), Phi(d) = 222 +/- 30 (10(9)), and Phi(b) = 5.2 +/- 0.4 (10(9) min(-1)). The model also allows one to quantify the beta-cell times of response to increasing and decreasing glucose stimulus, equal to 5.7 +/- 2.2 (min) and 17.8 +/- 2.0 (min), respectively. In conclusion, the graded glucose infusion protocol, interpreted with a minimal model of C-peptide secretion and kinetics, provides a quantitative assessment of pancreatic function in an individual. Its application to various physiopathological states should provide novel insights into the role of insulin secretion in the development of glucose intolerance.

Diagnosis of the polycystic ovary syndrome in adolescence: comparison of adolescent and adult hyperandrogenism.

We performed gonadotropin releasing hormone agonist (GnRHag) tests on 23 consecutive hyperandrogenic girls 9.9-17.5 years of age who were referred to our pediatric endocrinology clinic with symptoms suggestive of PCOS. They were compared to contemporaneously studied groups of adult normal and hyperandrogenic women. We found that hyperandrogenic adolescents had clinical and endocrine features similar to those of hyperandrogenic adults. However, there were some noteworthy unique features of adolescent hyperandrogenism, such as presentation in mid-childhood with premature pubarche and the occasional diagnosis before the age of 10 years. Some differences between adolescents and adults were statistically significant, for example, pelvic ultrasonography was not as helpful in the diagnosis of FOH as it is in adults. Nevertheless, a number of questions about the development of the ovarian dysfunction remain to be answered. For example, we are unable to diagnose ovarian dysfunction before puberty or in early puberty, and the relationship of "physiologic adolescent anovulation" to PCOS remains to be defined.

Glucose intolerance in the polycystic ovary syndrome: role of the pancreatic beta-cell.

Women with polycystic ovary syndrome (PCOS) are at increased risk of developing diabetes mellitus type 2. Insulin resistance plays a key role in the predisposition to diabetes in PCOS; however, defects in insulin secretion also appear to contribute to its development. Since diabetes mellitus is not a universal consequence in PCOS, however, it is important to develop means to identify those women who are at highest risk. In this way, it may become possible to delay or even prevent the onset of diabetes mellitus in later life. Identification of genetic factors and use of pharmacological agents may allow early identification of those women with PCOS who are at greatest risk for development of diabetes mellitus type 2.

Molecular analysis of the gonadotropin-releasing hormone receptor in patients with polycystic ovary syndrome.

OBJECTIVE: To determine whether a mutation in the GnRH receptor gene is responsible for polycystic ovary syndrome (PCOS). DESIGN: Molecular analysis of human genomic DNA. SETTING: Academic research environment. PATIENT(S): Eighty patients with PCOS. INTERVENTION(S): Extraction and polymerase chain reaction (PCR) analysis of genomic DNA, confirmation of PCR products by ethidium bromide staining of agarose gels after electrophoresis, denaturing gradient gel electrophoresis of PCR products, and photography. MAIN OUTCOME MEASURE(S): Mutations in the GnRH receptor of women with PCOS. RESULT(S): Denaturing gradient gel electrophoresis revealed no mutations in the exonic sequence encoding the open reading frame of the GnRH receptor. CONCLUSION(S): A mutation in the GnRH receptor gene is unlikely to be the underlying cause of PCOS in most patients. The molecular basis of this disorder remains unknown.

Thirty-seven candidate genes for polycystic ovary syndrome: strongest evidence for linkage is with follistatin.

Polycystic ovary syndrome (PCOS) is a common endocrine disorder of women, characterized by hyperandrogenism and chronic anovulation. It is a leading cause of female infertility and is associated with polycystic ovaries, hirsutism, obesity, and insulin resistance. We tested a carefully chosen collection of 37 candidate genes for linkage and association with PCOS or hyperandrogenemia in data from 150 families. The strongest evidence for linkage was with the follistatin gene, for which affected sisters showed increased identity by descent (72%; chi(2) = 12.97; nominal P = 3.2 x 10(-4)). After correction for multiple testing (33 tests), the follistatin findings were still highly significant (P(c) = 0.01). Although the linkage results for CYP11A were also nominally significant (P = 0.02), they were no longer significant after correction. In 11 candidate gene regions, at least one allele showed nominally significant evidence for population association with PCOS in the transmission/disequilibrium test (chi(2) >/= 3.84; nominal P < 0.05). The strongest effect in the transmission/disequilibrium test was observed in the INSR region (D19S884; allele 5; chi(2) = 8.53) but was not significant after correction. Our study shows how a systematic screen of candidate genes can provide strong evidence for genetic linkage in complex diseases and can identify those genes that should have high (or low) priority for further study.

Insulin-lowering therapeutic modalities for polycystic ovary syndrome.

This article summarizes the relationship between insulin and androgen excess, with a focus on what is known regarding two related issues in polycystic ovary syndrome: (1) defects in insulin secretion in PCOS and their role in the development of glucose intolerance in this population; and (2) pharmacologic interventions designed to attenuate hyperinsulinemia and its sequelae in PCOS.

Prevalence of impaired glucose tolerance and diabetes in women with polycystic ovary syndrome.

OBJECTIVE: NIDDM occurs commonly among women with polycystic ovary syndrome (PCOS). The prevalence and natural history of its precursor, impaired glucose tolerance (IGT), is less well known. The objective of this study was to characterize the prevalence and incidence of glucose intolerance in a large cohort of women with well-characterized PCOS. RESEARCH DESIGN AND METHODS: A total of 122 women with clinical and hormonal evidence of PCOS were recruited from the Medicine, Endocrinology, Gynecology, and Pediatrics Clinics at the University of Chicago. All women had a standard oral glucose tolerance test (OGTT) with measurement of glucose and insulin levels. A subset of 25 women were subsequently restudied with the aim of characterizing the natural history of glucose tolerance in PCOS. RESULTS: Glucose tolerance was abnormal in 55 (45%) of the 122 women: 43 (35%) had IGT and 12 (10%) had NIDDM at the time of initial study. The women with NIDDM differed from those with normal glucose tolerance in that they had a 2.6-fold higher prevalence of first-degree relatives with NIDDM (83 vs. 31%, P < 0.01 by chi 2) and were significantly more obese (BMI 41.0 +/- 2.4 vs. 33.4 +/- 1.1 kg/m2, P < 0.01). For the entire cohort of 122 women, there was a significant correlation between fasting and 2-h glucose concentrations (r = 0.76, P < 0.0001); among the subset with IGT, the fasting glucose concentration was poorly predictive of the 2-h level (r = 0.25, NS). After a mean follow-up of 2.4 +/- 0.3 years (range 0.5-6.3), 25 women had a second OGTT. The glucose concentration at 2 h during the second glucose tolerance test was significantly higher than the 2-h concentration during the first study (161 +/- 9 vs. 139 +/- 6 mg/dl, P < 0.02). CONCLUSIONS: The prevalence of IGT and NIDDM in women with PCOS is substantially higher than expected when compared with age- and weight-matched populations of women without PCOS. The conversion from IGT to NIDDM is accelerated in PCOS. The fasting glucose concentration does not reliably predict the glucose concentration at 2 h after an oral glucose challenge, particularly among those with IGT, the subgroup at highest risk for subsequent development of NIDDM. We conclude that women with PCOS should periodically have an OGTT and must be closely monitored for deterioration in glucose tolerance.

Treatment with the oral antidiabetic agent troglitazone improves beta cell responses to glucose in subjects with impaired glucose tolerance.

Impaired glucose tolerance (IGT) is associated with defects in both insulin secretion and action and carries a high risk for conversion to non-insulin-dependent diabetes mellitus (NIDDM). Troglitazone, an insulin sensitizing agent, reduces glucose concentrations in subjects with NIDDM and IGT but is not known to affect insulin secretion. We sought to determine the role of beta cell function in mediating improved glucose tolerance. Obese subjects with IGT received 12 wk of either 400 mg daily of troglitazone (n = 14) or placebo (n = 7) in a randomized, double-blind design. Study measures at baseline and after treatment were glucose and insulin responses to a 75-g oral glucose tolerance test, insulin sensitivity index (SI) assessed by a frequently sampled intravenous glucose tolerance test, insulin secretion rates during a graded glucose infusion, and beta cell glucose-sensing ability during an oscillatory glucose infusion. Troglitazone reduced integrated glucose and insulin responses to oral glucose by 10% (P = 0.03) and 39% (P = 0.003), respectively. SI increased from 1.3+/-0.3 to 2.6+/-0.4 x 10(-)5min-1pM-1 (P = 0.005). Average insulin secretion rates adjusted for SI over the glucose interval 5-11 mmol/liter were increased by 52% (P = 0.02), and the ability of the beta cell to entrain to an exogenous oscillatory glucose infusion, as evaluated by analysis of spectral power, was improved by 49% (P = 0.04). No significant changes in these parameters were demonstrated in the placebo group. In addition to increasing insulin sensitivity, we demonstrate that troglitazone improves the reduced beta cell response to glucose characteristic of subjects with IGT. This appears to be an important factor in the observed improvement in glucose tolerance.

Troglitazone improves defects in insulin action, insulin secretion, ovarian steroidogenesis, and fibrinolysis in women with polycystic ovary syndrome.

Women with polycystic ovary syndrome (PCOS) are characterized by defects in insulin action, insulin secretion, ovarian steroidogenesis, and fibrinolysis. We administered the insulin-sensitizing agent troglitazone to 13 obese women with PCOS and impaired glucose tolerance to determine whether attenuation of hyperinsulinemia ameliorates these defects. All subjects had oligomenorrhea, hirsutism, polycystic ovaries, and hyperandrogenemia. Before and after treatment with troglitazone (400 mg daily for 12 weeks), all had 1) a GnRH agonist (leuprolide) test, 2) a 75-g oral glucose tolerance test, 3) a frequently sampled iv glucose tolerance test to determine the insulin sensitivity index and the acute insulin response to glucose, 4) an oscillatory glucose infusion to assess the ability of the beta-cell to entrain to glucose as quantitated by the normalized spectral power for the insulin secretion rate, and 5) measures of fibrinolytic capacity [plasminogen activator inhibitor type 1 (PAI-1) and tissue plasminogen activator]. There was no change in body mass index (39.9 +/- 1.4 vs. 40.2 +/- 1.4 kg/m2) or body fat distribution after treatment. Both the fasting (91 +/- 3 vs. 103 +/- 3 mg/dL; P < 0.001) and 2 h (146 +/- 8 vs. 171 +/- 6 mg/dL; P < 0.02) plasma glucose concentrations during the oral glucose tolerance test declined significantly. There was a concordant reduction in glycosylated hemoglobin to 5.7 +/- 0.1 from a pretreatment level of 6.1 +/- 0.1% (P < 0.03). Insulin sensitivity increased from 0.58 +/- 0.14 to 0.95 +/- 0.26 10(-5) min-1/pmol.L (P < 0.01) after treatment as did the disposition index (745 +/- 135 vs. 381 +/- 96; P < 0.05). The ability of the beta-cell to appropriately detect and respond to an oscillatory glucose infusion improved significantly after troglitazone treatment; the normalized spectral power for the insulin secretion rate increased to 5.9 +/- 1.1 from 4.3 +/- 0.8 (P < 0.05). Basal levels of total testosterone (109.3 +/- 15.2 vs. 79.4 +/- 9.8 ng/dL; P < 0.05) and free testosterone (33.3 +/- 4.0 vs. 21.2 +/- 2.6 pg/mL; P < 0.01) declined significantly after troglitazone treatment. Leuprolide-stimulated levels of 17-hydroxyprogesterone, androstenedione, and total testosterone were significantly lower posttreatment compared to pretreatment. The reduction in androgen levels occurred independently of any changes in gonadotropin levels. A decreased functional activity of PAI-1 in blood (from 12.7 +/- 2.8 to 6.3 +/- 1.4 AU/mL P < 0.05) was associated with a decreased concentration of PAI-1 protein (from 64.9 +/- 9.1 to 44.8 +/- 6.1 ng/mL; P < 0.05). No change in the functional activity of tissue plasminogen activator (from 5.3 +/- 0.4 to 5.1 +/- 0.5 IU/mL) was observed despite a decrease in its concentration (from 9.6 +/- 0.9 to 8.2 +/- 0.7 ng/mL; P < 0.05). The marked reduction in PAI-1 could be expected to improve the fibrinolytic response to thrombosis in these subjects. We conclude that administration of troglitazone to women with PCOS and impaired glucose tolerance ameliorates the metabolic and hormonal derangements characteristic of the syndrome. Troglitazone holds potential as a useful primary or adjunctive treatment for women with PCOS.

Relation of functional ovarian hyperandrogenism to non-insulin dependent diabetes mellitus.

Up to 40% of women with polycystic ovary syndrome (PCOS) demonstrate some degree of glucose intolerance, either impaired glucose tolerance (IGT) or non-insulin dependent diabetes mellitus (NIDDM). Defects in insulin action have long-been recognized as characteristic in these women. Recently, evidence has been obtained which documents that insulin secretory dysfunction also contributes significantly to the observed glucose intolerance. This chapter will focus on the recent evidence supporting the specific roles of disordered insulin secretion and action, in the development of glucose intolerance in PCOS. In addition, the use of pharmacological agents that modify insulin action as therapeutic options for women with PCOS, will be discussed.

Effects of metformin on insulin secretion, insulin action, and ovarian steroidogenesis in women with polycystic ovary syndrome.

Hyperinsulinemia contributes to the ovarian androgen overproduction and glucose intolerance of polycystic ovary syndrome (PCOS). We sought to determine whether metformin would reduce insulin levels in obese, nondiabetic women with PCOS during a period of weight maintenance and thus attenuate the ovarian steroidogenic response to the GnRH agonist leuprolide. All subjects (n = 14) had an oral glucose tolerance test, a GnRH agonist (leuprolide) test, a frequently sampled iv glucose tolerance test, graded and oscillatory glucose infusions, and a dual energy x-ray absorptiometry scan before and after treatment with metformin (850 mg, orally, three times daily for 12 weeks). With weight maintenance (body mass index: pretreatment, 39.0 +/- 7.7 kg/m2, posttreatment, 39.1 +/- 7.9 kg/m2), oral glucose tolerance, insulin sensitivity (Si; 0.87 +/- 0.82 vs. 0.74 +/- 0.63 x 10(-5) min-1/ pmol.L), and the relationship between Si and first phase insulin secretion (AIRg vs. Si) were not improved by metformin. The insulin secretory response to glucose, administered in both graded and oscillatory fashions, was likewise unaltered in response to metformin. Free testosterone levels remained about 2-fold elevated (pretreatment, 26.6 +/- 12.7 pg/mL; posttreatment, 22.4 +/- 9.8 pg/mL). Both basal and stimulated LH and FSH levels were unaffected by metformin. The mean responses to leuprolide of 17-hydroxyprogesterone (pretreatment, 387 +/- 158 ng/dL; posttreatment, 329 +/- 116 ng/dL) as well as those of the other ovarian secretory products (androstenedione, dehydroepiandrosterone, progesterone, and estradiol) were not attenuated by metformin. We conclude that hyperinsulinemia and androgen excess in obese nondiabetic women with PCOS are not improved by the administration of metformin.

Acute hormonal responses to the gonadotropin releasing hormone agonist leuprolide: dose-response studies and comparison to nafarelin--a clinical research center study.

The hormonal responses to single subcutaneous injection of the GnRH agonist nafarelin have been shown to have considerable potential as a diagnostic test in a number of settings. Since nafarelin injection is no longer produced, studies were conducted to determine the dosage of leuprolide that would yield equivalent responses. Nafarelin 100 micrograms stimulates LH and FSH for 24 h, releasing about 7-fold more gonadotropin than this dose of natural GnRH, which accounts for its ability to elicit gonadal steroid responses. Normal adult men and women were randomized to receive leuprolide doses of 0.1, 1.0, or 10 micrograms/kg; a study extension evaluated doses up to 20 micrograms/kg in men. The responses of LH, FSH, testosterone, and estradiol were monitored for 24 h, and the data were compared to those previously obtained on nafarelin. Leuprolide dose of 10 micrograms/kg yielded LH responses similar to 1-1.5 micrograms/kg nafarelin. However, this leuprolide dose unexpectedly released less FSH than nafarelin. Nevertheless, the gonadotropin responses were sufficient to elicit equivalent or greater sex steroid responses to leuprolide. These studies also further delineated sex-specific differences in pituitary responsiveness to challenge with GnRH agonists: men had a significantly lower baseline FSH level, greater LH release within the first hour, and lesser secretion of LH and FSH over the 24-h period. These studies indicate that leuprolide in a dosage of 10 micrograms/kg would be expected to be efficacious in testing the pituitary-gonadal axis in men and women.

The GENNID Study. A resource for mapping the genes that cause NIDDM.

OBJECTIVE: To develop a resource, consisting of comprehensive data and lymphoblastoid cell lines, of well-characterized NIDDM families that will be available to the scientific community for genetic studies of NIDDM. RESEARCH DESIGN AND METHODS: Non-Hispanic white, Hispanic, African-American, and Japanese-American multiplex NIDDM families, with a minimum of one affected sib-pair, are being collected by the eight Harold Rifkin Family Acquisition Centers. Detailed family and medical histories are obtained from all participants. Family members with diabetes have fasting blood samples drawn, while nondiabetic family members have an oral glucose tolerance test and, when possible, insulin sensitivity and insulin secretion measurements by frequently sampled intravenous glucose tolerance testing or euglycemic insulin clamp. Lymphoblastoid cell lines are established for all participants. RESULTS: Over 1,400 individuals from approximately 220 families have been studied since the start of the GENNID (Genetics of NIDDM) program in July 1993. The goal is that by July 1997, data from 300 non-Hispanic white families, > 100 Hispanic families, > 100 African-American families, and 15 Japanese-American families will have been collected. CONCLUSIONS: The identification of the genes responsible for NIDDM may now be achievable, but only if sound phenotypic data are linked to genetic material from a large number of well-described multiplex families. The GENNID project of the American Diabetes Association is creating a comprehensive resource that will expedite the identification of the genetic basis of NIDDM.

Insulin secretory defects in polycystic ovary syndrome. Relationship to insulin sensitivity and family history of non-insulin-dependent diabetes mellitus.

The increased prevalence of non-insulin-dependent diabetes mellitus (NIDDM) among women with polycystic ovary syndrome (PCOS) has been ascribed to the insulin resistance characteristic of PCOS. This study was undertaken to determine the role of defects in insulin secretion as well as familial factors to the predisposition to NIDDM seen in PCOS. We studied three groups of women: PCOS with a family history of NIDDM (PCOS FHx POS; n = 11), PCOS without a family history of NIDDM (PCOS FHx NEG; n = 13), and women without PCOS who have a family history of NIDDM (NON-PCOS FHx POS; n = 8). Beta cell function was evaluated during a frequently sampled intravenous glucose tolerance test, by a low dose graded glucose infusion, and by the ability of the beta cell to be entrained by an oscillatory glucose infusion. PCOS FHx POS women were significantly less likely to demonstrate appropriate beta cell compensation for the degree of insulin resistance. The ability of the beta cell to entrain, as judged by the spectral power for insulin secretion rate, was significantly reduced in PCOS FHx POS subjects. In conclusion, a history of NIDDM in a first-degree relative appears to define a subset of PCOS subjects with a greater prevalence of insulin secretory defects. The risk of developing NIDDM imparted by insulin resistance in PCOS may be enhanced by these defects in insulin secretion.