Testosterone effect on insulin content, messenger ribonucleic acid levels, promoter activity, and secretion in the rat.

Coexistence of hyperinsulinemia and hyperandrogenism in women has been frequently described. Most of the studies addressing this issue have focused on the mechanisms by which insulin produces hyperandrogenism. In the present study, we analyzed the effects of testosterone in vivo and in vitro upon insulin gene expression and release in the rat. Our studies demonstrate that testosterone increases insulin messenger RNA (mRNA) levels in vitro as well as in vivo. In both prepuberal and intact adult rats, serum testosterone concentrations were positively correlated with insulin mRNA levels and insulin concentration in serum. Testosterone deprivation after gonadectomy decreased both insulin gene expression and serum insulin concentration. Insulin mRNA levels were partially restored after 3 days of testosterone administration and serum insulin was 80% and 27% above baseline values at 5 and 7 days posttreatment. Primary cultured pancreatic islets treated with the sexual steroid increased about 80% insulin mRNA, as well as protein, and release. In transfected islets, testosterone increased the activity of the -410 bp rat insulin promoter I by 154%. These data demonstrate that testosterone has a direct effect upon pancreatic islet function by favoring insulin gene expression and release.

Self-priming effect of luteinizing hormone-human chorionic gonadotropin (hCG) upon the biphasic testicular response to exogenous hCG. I. Serum testosterone profile.

The present study was conducted to investigate whether the early (2-8 h) testicular response to a single dose of exogenous hCG depends on previous exposure to LH activity. Four different groups of subjects were studied: 1) four normal adult men [Tanner stage-G5 (T-G5)] and one late pubertal subject (T-G4); 2) normal prepubertal (T-G1) and early- and midpubertal boys (T-G2 and T-G3) (n = 4-6 each); 3) five patients with hypogonadotropic hypogonadism (HH); and 4) two patients with the complete form of the androgen insensitivity syndrome. Each subject received an im injection of hCG (40 IU/kg) on day 1 and blood samples were drawn before and 1-8, 24, 48, and 72 h after injection. At 96 h, a second dose of hCG was given (80 IU/kg) and blood samples were obtained at the same times as after the first hCG dose. Serum testosterone (T) was measured by RIA. The first dose of hCG evoked a biphasic response of serum T in groups T-G2 to T-G5 as well as in the two patients with the complete form of the androgen insensitivity syndrome. The early peak was at 2-7 h, whereas the late T peak was at 48-72 h after injection. In T-G1 children and in patients with HH, the early response did not occur [T-G1, from 129 +/- 43 (SEM) to 288 +/- 127 pg/ml (P greater than 0.05); HH, 79 +/- 18 to 107 +/- 12 (P greater than 0.05) pg/ml], and the late peak was attenuated as compared with the pubertal boys. There were not significant differences in the responses of the T-G1 and the HH groups. After the second dose, all groups had biphasic T responses, although they varied in magnitude. These results demonstrate that previous exposure to LH activity is an obligatory prerequisite for the early peak of the hCG-mediated biphasic testicular response, and that a single dose of hCG has a priming effect that is sufficient to ensure a biphasic response to a second dose of hCG given 96 h later.

Heterogeneity of serum prolactin throughout the menstrual cycle and pregnancy in hyperprolactinemic women with normal ovarian function.

We have demonstrated the selective secretion of high mol wt PRL series (big big PRL) in women with hyperprolactinemia and normal ovarian function. This observation suggests that big big PRL is immunologically similar, but biologically less active, than monomeric or little PRL. In this study we determined the molecular size heterogeneity of immunoreactive PRL in the serum from two ovulatory hyperprolactinemic women (subjects A and B) who had large amounts of serum big big PRL during a menstrual cycle and/or gestation. Serum samples obtained throughout the menstrual cycle (days 6, 10, 14, 17, 23, and 28, taking as day 1 the first day of bleeding) and pregnancy (weeks 7, 9, 11, 15, 20, 25, 30, 34, and 38) were fractionated by gel filtration chromatography. PRL was identified in column eluates by specific RIA. Two additional pregnant women, one with a bromocriptine-treated PRL-secreting adenoma (subject C), and a normal woman (subject D) were studied. Big big PRL was the predominant species throughout the different phases of the menstrual cycle in subject B, comprising 70-80% of the total immunoreactive PRL. Most of the remainder was big PRL, and little PRL was present in only small amounts (6-12%) during the luteal phase. During their pregnancies, the serum PRL in subjects A and B initially was mostly big big PRL, but later in gestation the PRL composition shifted from the high mol wt variants to little PRL. The infant's cord (subject A) and peripheral (subject B) serum at birth contained appreciable quantities of big big and big PRL, respectively. These results indicate that structural changes in PRL occur during pregnancy and the menstrual cycle which are probably influenced by the hormonal environment. In addition, the occurrence of larger mol wt PRL species in the serum of the infant of a hyperprolactinemic mother suggests that the presence of high proportions of big big PRL in the serum is genetically determined.

A reliable endocrine test with human menopausal gonadotropins for diagnosis of true hermaphroditism in early infancy.

In true hermaphroditism diverse phenotypes and karyotypes are found; there are no distinctive laboratory features that can distinguish it from other intersex disorders, thus the diagnosis is made by the histological findings. Existence of Leydig cells is demonstrated by testosterone levels above the female range; however, presence of ovarian tissue cannot be ascertained because of the absence of a reliable functional test. Unless appropriate biopsies are performed or the whole gonad is removed, there is a risk of not diagnosing true hermaphroditism. To find a reliable test that can differentiate patients with true hermaphroditism from those with other intersex disorders, we investigated the estradiol (E2) response to human menopausal gonadotropins (hMG) in infants with genital ambiguity. These results were correlated with the histological findings. Eleven infants with genital ambiguity and four with a high scrotal testis were stimulated every 12 h with 2 IU/kg hMG. If E2 rose above 80 pg/mL (cut-off point), the test was discontinued; if after 7 days E2 remained below 80 pg/mL, the hMG dose was doubled and stimulation extended for 7 additional days. In five patients in whom true hermaphroditism was later histologically demonstrated, E2 rose above 80 pg/mL. In two of them, ovarian tissue was removed and hMG stimulation repeated; no response above our cut-off point was observed during the second test. The maximal E2 response to hMG in the remaining 10 individuals was 43 pg/mL; after laparotomy or gonadal biopsies no ovarian tissue was found. The hMG stimulation test can be considered a reliable and safe dynamic procedure for demonstrating the presence or absence of ovarian tissue in infants with genital ambiguity.

Microheterogeneity of anterior pituitary FSH in the male rat: isoelectric focusing pattern throughout sexual maturation.

Anterior pituitary glands were removed from male rats at 5, 10, 15, 18, 21, 28, 30, 40, 50 and 90 days of age, and the multiple forms of FSH present within them were separated by polyacrylamide gel-isoelectric focusing (PAGE-IEF; pH range 3.0-8.0). Gel eluents were analysed for FSH content by radioimmunoassay (RIA) and a specific radioreceptor assay (RRA). All pituitaries studied exhibited one or more peaks of immunoactive FSH within a pH range of 7.0-3.0; the major peak exhibited an isoelectric point (pI) of 4.9-4.0. Between 25 and 56% of anterior pituitary FSH obtained from rats 5-30 days old focused within a pH range of 4.9-4.5, whilst in older animals (greater than or equal to 40 days) this pH range contained 17-27% of the total FSH recovered. In contrast, in animals 40-90 days old, the greatest proportion of immunoactive FSH (42-62% of the total immunoactivity recovered) focused within a pH range of 4.4-4.0; further, only these groups of animals exhibited a significant proportion of anterior pituitary FSH with a pI less than or equal to 3.9. Between 14 and 21% of total FSH from 5- to 30-day-old rats focused within a pH range of 5.4-5.0, whereas in older animals this pH range contained 6-9% of the total FSH recovered. These shifts in FSH pI occurred at the time of appearance of spermiogenesis, at 45 days of age. Although the ratio of the concentration of FSH measured by RRA to that measured by RIA declined as the pI of the anterior pituitary FSH decreased throughout a pH range of 7.0-4.0, the most acidic FSH molecules (pI less than 4.0) showed an abrupt increase in that ratio. These results demonstrate that the transition from sexual immaturity to adulthood is accompanied by qualitative changes of intracellular pituitary FSH. They contrast with previous findings in female rats in which a shift to less acidic anterior pituitary FSH forms was detected at the time of vaginal opening, thus indicating the existence of a sexual dichotomy in terms of the action of gonadal steroids on the type of FSH molecule synthesized by the anterior pituitary gland.

Changes in the responsiveness of prolactin secretion to dopaminergic blockade and TRH stimulation throughout sexual maturation in men.

The pituitary prolactin (PRL) response to domperidone (DOM; a dopaminergic antagonist) and TRH administration in human males during different stages of sexual maturation was investigated. Dopaminergic blockade caused an immediate and significant PRL release in all subjects, regardless of the stage of pubertal development. Even though the mean values of peak PRL levels, magnitude of PRL response (delta PRL) and areas under the PRL curve were not significantly different among the different groups, all these parameters showed a clear tendency to increase in parallel to the stage of pubertal development, as indicated by significant positive correlations between age and pubertal stage of the subjects and the magnitude of their PRL response to DOM (r = 0.661, p less than 0.01 and r = 0.536, p = 0.01, respectively). Significant positive correlations also were found between the serum sex steroid hormone concentrations and the PRL response to dopaminergic blockade (r = 0.774, p = 0.02 and r = 0.554, p = 0.01, respectively). In contrast to these findings, no significant differences or tendencies were detected in the PRL responses to TRH among the different subject groups. The different patterns of PRL response to DOM and TRH throughout male puberty might be due to differences in pituitary thresholds for sex steroids between the dopamine- and TRH-dependent intracellular pools.

Pharmacokinetics and pharmacodynamics of 25-mg estradiol implants in postmenopausal Mexican women.

OBJECTIVE: To assess the serum concentrations of estradiol (E2), estrone (E1), gonadotrophins, sex hormone-binding globulin, and lipids, and to determine degree of symptom relief after subcutaneous implantation of 25 mg estradiol in postmenopausal Mexican women. DESIGN: Fifteen postmenopausal, hysterectomized women participated in an open, observational study. Blood samples were obtained before implantation and at regular intervals during a study period of 24 weeks. Climacteric symptoms were evaluated by means of the Greene climacteric scale. Wilcoxon's test was performed on the paired results of pre-and postimplantation values. RESULTS: Serum concentrations of E2 obtained after implantation were fairly constant, remaining within the early follicular range for the entire study period of 24 weeks, and were associated with significant symptom relief. A physiological, premenopausal E2:E1 ratio was achieved. No significant metabolic changes occurred. Side effects were estrogenic in nature and no removal of implant was required. CONCLUSIONS: Subcutaneous implantation of 25 mg estradiol results in physiological, premenopausal estrogen concentrations in most women and is associated with considerable symptom relief without inducing significant adverse metabolic effects.

Cholesterol side-chain cleavage and 11 beta-hydroxylation are inhibited by gossypol in adrenal cortex mitochondria.

Cholesterol side-chain cleavage and 11 beta-hydroxylation were assessed in isolated adrenal cortex mitochondria by formation of pregnenolone and corticosterone, respectively, in the presence and absence of gossypol. Pregnenolone biosynthesis was inhibited when increasing concentrations of gossypol were added. The control value of 4 nmol min-1 mg-1 dropped to 2 nmol min-1 mg-1 with 30 microM of the drug in the incubation medium. A more pronounced inhibitory effect was observed upon 11 beta-hydroxylation of steroids; I50 was 11 microM. Seventy-five percent of corticosterone production was impaired when 30 microM of gossypol were present. Bovine serum albumin prevented and reversed the inhibitory action of the drug. Kinetic studies showed a linear mixed type inhibition, suggesting a direct action of the drug upon the enzymatic complex. This study demonstrates a direct inhibitory effect of gossypol upon the steroidogenic enzymes located in the inner mitochondrial membrane of the adrenal cortex.

Modulation of serum testosterone and autonomic function through stimulation of the male human vomeronasal organ (VNO) with pregna-4,20-diene-3,6-dione.

In mammals, external chemosensory signals from conspecifics of the opposite sex acting on vomeronasal organ receptors can modulate the release of gonadotropins. There is developmental, anatomical and functional evidence showing that the human vomeronasal organ (VNO) has the characteristics of a chemosensory organ. We have been using naturally occurring human pheromones to serve as models for designing novel synthetic compounds that we call vomeropherins. In previous publications we reported that vomeropherin pregna-4,20-diene-3,6-dione (PDD) delivered to the VNO of normal female and male human volunteers significantly affected male subjects only, decreasing respiration and cardiac frequency, augmenting alpha brain waves, and significantly decreasing serum luteinizing hormone (LH) and follicle stimulating hormone (FSH). Results of the present work confirm that PDD produces a local dose-dependent effect in the male human VNO. This is followed by a mild parasympathomimetic effect characterized by 10% increase of vagal tone, together with decreased frequency of electrodermal activity events. Furthermore, PDD locally delivered to the male human VNO significantly decreases serum LH and testosterone (p < 0.01). The present results contribute additional evidence supporting the functionality of the human VNO and its repercussions in autonomic and psychophysiological functions, as well as in neuroendocrine secretions.

The functionality of the human vomeronasal organ (VNO): evidence for steroid receptors.

The human vomeronasal organ (VNO) is an anatomical entity which is generally considered to be vestigial or non-functional. Nevertheless, a steroidal vomeropherin applied to the human VNO, results in changes of autonomic function, pulsatile release of luteinizing and follicle-stimulating hormones, autonomic and electroencepholographic activity. The vomeropherin pregna-4,20-diene-3,6-dione (PDD) was delivered as pulses in an air stream directed into the lumen of the VNO or to the surface of the olfactory epithelium and respiratory epithelium of the nasal septum. Single stimuli at a concentration of 10(-10) to 10(-8) M produced dose-dependent changes of the electrovomerogram. No significant effects were observed when the same applicator delivered identical stimuli to the nasal respiratory epithelium or to the olfactory epithelium. Administration of the vomeropherin to male subjects changed gonadotropin pulsatility. In males, PDD (5 x 10(9) M) decreased luteinizing hormone (LH) pulsatility which resulted in a statistically significant reduction of plasma LH levels (P < 0.009) and follicle-stimulating hormone (FSH) pulsatility (P < 0.021), but it produced no significant effects in female subjects. Prolactin (PRL) was not significantly affected by this vomeropherin in either male or female subjects. These data demonstrate, for the first time, the existence of a functional vomeronasal-pituitary pathway in adult humans. In addition to the effect on gonadotropin pulsatility, the vomeropherin also produces concurrent reflex autonomic effects after VNO stimulation. These included decreased respiratory frequency, increased cardiac frequency, and event-related changes of electrodermal activity and EEG pattern. Therefore, this investigation also provides evidence for functional connections between the VNO and a variety of hypothalamic areas in adult humans.

Synthesis of steroids in pancreas: evidence of cytochrome P-450scc activity.

In pancreas, the activities of several sex steroid-transforming enzymes have been reported. Data have been obtained in perfused organs, total tissue homogenates, and subcellular organelles. These data, concurrent with the description of the presence of ligand-regulated steroid receptors, as well as the sexually dimorphic behavior of some pancreatic tumors, are clear evidence in support of the participation of steroid hormones in the pancreatic function. In this study, the steroidogenic ability of the pancreas was demonstrated by two different methods: (a) in tissue homogenates, by the identification of cytochrome P-450scc gene (CYP11A) transcripts after reverse transcription-polymerase chain reaction amplification (RT-PCR); and (b) in isolated mitochondria by the glutethimide-dependent inhibition of cholesterol-pregnenolone biotransformation. The results obtained in a series of independent experiments showed that (a) the pancreatic tissue possessed transcriptional activity of the CYP11A gene, although to a lesser extent than the typical steroidogenic tissues, and (b) isolated mitochondria obtained from the pancreas were able consistently to synthesize pregnenolone; furthermore, the addition of the specific inhibitor aminoglutethimide (AMG) blocked its synthesis. On the whole, these findings are interpreted as clear evidences of the activity of the cytochrome P-450scc enzymatic complex (P450scc), responsible for the transformation of cholesterol into pregnenolone and considered the first and limiting step in steroid biosynthesis.

Low serum testosterone/dihydrotestosterone ratio in patients with pancreatic carcinoma.

Serum testosterone, its metabolite 5 alpha-dihydrotestosterone, and the testosterone/dihydrotestosterone ratio were investigated in 22 male patients with proven pancreatic cancer, and compared with values from male patients with chronic pancreatitis (n = 21) and with nonpancreatic gastrointestinal tumors (n = 19). Testosterone and the testosterone/dihydrotestosterone ratio were significantly lower (p less than 0.001) in the pancreatic cancer group when they were compared with the other two groups. There was no significant difference in the dihydrotestosterone values between cancer groups. A testosterone/dihydrotestosterone ratio of less than 5 clearly distinguished most of the patients (20/22) with cancer of the pancreas from those with other tumors or chronic pancreatitis. The results suggest an alteration in the serum androgen profile in these patients. Therefore, the testosterone/dihydrotestosterone ratio could be a useful marker in the diagnosis of pancreatic carcinoma in male patients.

Pancreatic cancer and androgen metabolism: high androstenedione and low testosterone serum levels.

Serum androstenedione and testosterone levels were measured in 39 male patients with pancreatic cancer, and compared with the values obtained from 37 male patients with chronic pancreatitis or benign obstructive jaundice, and with those from 36 male patients with other gastrointestinal malignancies. Mean androstenedione values were significantly higher in the pancreatic cancer patients when compared to both control groups, and mean testosterone levels were significantly lower. The testosterone/androstenedione ratio was calculated and was also found to be significantly lower in the patients with pancreatic cancer. There was no difference in this ratio or in the androstenedione or testosterone levels when comparing both control groups. In two patients with stage I pancreatic cancer, serum androstenedione and testosterone levels were significantly altered, and returned to normal values after successful resection. These results confirm previous findings indicating that there is significant derangement in the androgen profile of patients with pancreatic cancer.

Androgen receptor in the rat pancreas: genetic expression and steroid regulation.

Androgens influence the incidence and prevalence of pancreatic cancer in humans and animal models. To our knowledge there has been molecular demonstration of the presence of neither the androgen receptor (AR) nor transcripts of the AR gene. Reverse-transcription polymerase chain reaction (RT-PCR)-Southern blotting was employed for molecular detection and measurement of the androgen receptor messenger ribonucleic acid (AR mRNA) in pancreas. Total RNA obtained from pancreas, prostate, seminal vesicles, and testes of neonatal and adult male and female rats, as well as castrated males substituted with testosterone cyclopentylate, was analyzed by Northern blot technique. Positive hybridization to AR cDNA was obtained in all tissues assayed but not in the pancreas. However, a clear AR 32P cDNA hybridization signal was obtained in pancreatic tissues after cDNA synthesis using RT-PCR-Southern blotting. The levels of the AR transcripts obtained by RT-PCR in the various pancreatic samples were as follows: adult females and neonatal animals > castrated adult males > adult males > castrated adult males substituted with testosterone. These results indicated that the pancreatic tissue possessed transcriptional activity of the AR gene, although to a lesser extent than the typical androgen responsive tissues (prostate and seminal vesicles). In conclusion, transcriptional activity of the AR gene in the pancreas seemed to be modulated by the androgenic milieu in the tissue similar to that reported for the classical androgen-responsive organs.

Testosterone biotransformation by the isolated perfused canine pancreas.

There is strong evidence indicating that the pancreas is under the influence of sex steroid hormones, and that it may even participate in their biosynthesis and metabolism. In the present study, [3H]testosterone was perfused into the isolated canine pancreas, and measured in the effluent with several of its metabolites (5 alpha-dihydrotestosterone, androstenedione, and estradiol). Results show that testosterone is readily transformed by the canine pancreas. The main product found in the effluent is androstenedione. The testis and spleen were also perfused with [3H]testosterone and used as controls. In both cases, this hormone appeared mostly unchanged in the effluent as compared to the pancreatic perfusion (p less than 0.0001). From our data, we conclude that the canine pancreas has the capacity to transform sex steroid hormones, and could be considered an extragonadal site of sex steroid biosynthesis.

Absorption of dihydrotestosterone (DHT) after its intramuscular administration.

In order to produce a sustained release system for natural androgens, two groups of six hypogonadal males received intramuscular (IM) 40 mg crystalline dihydrotestosterone (DHT), either with particle size of less than 50 microns (DHT-M) or between 100 and 150 microns (DHT-C). Serum DHT was analyzed through 51 days of follow-up. In the DHT-M group, serum DHT was above pretreatment values for 17 days, whereas in the DHT-C group, this period was extended over 50 days. The area under the serum concentration-time curve and the half-life of absorption calculated for the DHT-C group were greater than those obtained for the DHT-M group (55.1 ng/day/ml and 21 days vs. 14.5 ng/day/ml and 6 days; P less than 0.01). The authors conclude that DHT injection appears to be an effective and convenient technique for restoring serum physiologic DHT levels. This approach is suitable for long-term substitution therapy.

Variations in serum lipids and lipoproteins throughout the menstrual cycle.

One hundred fourteen women of reproductive age were included in a cross-sectional study with the aim of establishing the variations in serum lipids and lipoproteins during the menstrual cycle. Total cholesterol, triglycerides, and phospholipids were determined in whole serum and in the following lipoprotein fractions: very low-density lipoproteins (VLDL), low-density lipoproteins (LDL), and high-density lipoproteins, obtained by ultracentrifugation. A significant decrease was found in total cholesterol (P less than 0.05) and phospholipids (P less than 0.01) during the late luteal phase. The LDL cholesterol decreased during the luteal phase and VLDL cholesterol increased in the early and midluteal phases. The LDL phospholipids and VLDL triglycerides also showed a significant decrease during the luteal phase (P less than 0.01). The results of this investigation demonstrate major fluctuation in cholesterol, triglyceride, and phospholipid-lipoprotein composition during the menstrual cycle.

Ovarian function following a single administration of depo-medroxyprogesterone acetate (DMPA) at different doses.

The effects of a single administration of depo-medroxyprogesterone acetate (DMPA) at different doses upon ovarian function was studied in a group of healthy ovulating Mexican women. Single doses of DMPA of 25, 50, 100, and 150 mg were intramuscularly administered. Ovarian function was assessed by the measurement of the serum levels of 17 beta-estradiol and progesterone in blood samples drawn twice weekly for 6 months after DMPA administration. The results disclosed that ovulation was inhibited in all cases for at least 3 months following DMPA administration even at the lowest dose, whereas the return of luteal function exhibited a significant positive correlation with the dose of DMPA administered. As expected, follicular activity preceded that of luteal function in all subjects. A correspondence between serum medroxyprogesterone concentrations and ovarian function was found. The overall data indicated that the currently used contraceptive formulation (150 mg) is well above the effective pharmacologic range, and suggested that the dose can be substantially reduced without losing its anovulatory potency.

Insulin gene expression pattern in rat pancreas during the estrous cycle.

Sex steroid hormones influence insulin homeostasis and glucose metabolism, estradiol (E2) and progesterone (P4) induce changes in both fasting and postprandial insulinemia in rodents, however, insulin gene expression during estrous cycle is unknown. The aim of the present study was to determine an insulin gene expression pattern during the estrous cycle in the rat. Groups of 6 adult rats in each day of the estrous cycle were used. Serum P4, E2, testosterone (T) and insulin concentrations were determined by radioimmunoassay (RIA). A Northern blot analysis was performed to assess insulin gene expression in pancreatic tissue. We found a marked variation in insulin gene expression during the estrous cycle. The highest insulin expression was observed during the proestrus day. Interestingly, E2 and P4 but not T levels were correlated with changes in insulin mRNA content. The variations in serum insulin during the cycle were correlated with its mRNA content in pancreas. The overall results showed variations in serum insulin and insulin gene expression during estrous cycle of the rat that correlated with circulating E2 and P4 levels.

Hypothalamic dopaminergic tone and prolactin bioactivity in women with polycystic ovary syndrome.

BACKGROUND: The present study was carried out to investigate the functional significance of the reduced dopaminergic tone in subjects affected with polycystic ovary syndrome (PCOS). METHODS: Our group evaluated the response of pituitary PRL, LH, FSH, and TSH to the administration of a single 10-mg oral dose of the dopamine (DA) receptor antagonist metoclopramide in lean (n = 7) and obese (n = 8) PCOS women and in 11 regularly cycling age- and weight-matched controls (six lean and five obese). In addition, circulating PRL bioactivity was evaluated by its mitogenic activity on a lymphoma cell bioassay. RESULTS: Oral administration of metoclopramide resulted in a significant increase in serum PRL in all subjects; however, the highest increments, regardless of body mass index (BMI), were observed in control women (p <0.005). Measurements of PRL mitogenic activity on the Nb2 lymphoma cell bioassay revealed a significant increase in the bioactive/immunoreactive (B/I) ratio of PRL under basal and stimulated conditions in obese PCOS subjects (p <0.05). Mean fasting glucose/insulin and glucose/insulin-AUC ratios were significantly lower (p <0.001) in obese PCOS when compared with all other groups. CONCLUSIONS: These data support the existence of low DA hypothalamic tone in PCOS women that is likely involved in the inappropriate LH and PRL secretion frequently seen in this syndrome. In addition, our results suggest changes in PRL bioactivity in obese PCOS that may play a role in the development of hyperinsulinemia; however, whether PRL has a functional significance in the development of the metabolic disturbances frequently seen in PCOS remains to be elucidated.