Acute modulation of the hypothalamic-pituitary axis by intravenous testosterone in normal women

Androgen Inhibition of Reproductive Neuroendocrine Function in Females and Transgender Males

Ovarian function is controlled by pituitary secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH), which in turn are governed by gonadotropin releasing hormone (GnRH) secreted from the brain. A fundamental principle of reproductive axis regulation is negative feedback signaling by gonadal sex steroids back to the brain to fine-tune GnRH and gonadotropin secretion. Endogenous negative feedback effects can be mimicked by exogenous steroid treatments, including androgens, in both sexes. Indeed, a growing number of clinical and animal studies indicate that high levels of exogenous androgens, in the typically male physiological range, can inhibit LH secretion in females, as occurs in males. However, the mechanisms by which male-level androgens inhibit GnRH and LH secretion still remain poorly understood, and this knowledge gap is particularly pronounced in transgender men (individuals designated female at birth but identifying as male). Indeed, many transgender men take long-term gender-affirming hormone therapy that mimics male-level testosterone levels. The impact of such gender-affirming testosterone on the reproductive axis, both at the ovarian and neuroendocrine level, is a long-understudied area that still requires further investigation. Importantly, the few concepts of androgen actions in females mostly come from studies of polycystic ovary syndrome, which does not recapitulate a similar androgen milieu or a pathophysiology of inhibited LH secretion as occurs in testosterone-treated transgender men. This review summarizes clinical evidence indicating that exogenous androgens can impair neuroendocrine reproductive function in both female individuals and transgender men and highlights emerging experimental data supporting this in recently developed transgender rodent models.

Obesity-Related Hypogonadism in Women

Obesity-related hypogonadotropic hypogonadism is a well-characterized condition in men (termed male obesity-related secondary hypogonadism; MOSH); however, an equivalent condition has not been as clearly described in women. The prevalence of polycystic ovary syndrome (PCOS) is known to increase with obesity, but PCOS is more typically characterized by increased gonadotropin-releasing hormone (GnRH) (and by proxy luteinizing hormone; LH) pulsatility, rather than by the reduced gonadotropin levels observed in MOSH. Notably, LH levels and LH pulse amplitude are reduced with obesity, both in women with and without PCOS, suggesting that an obesity-related secondary hypogonadism may also exist in women akin to MOSH in men. Herein, we examine the evidence for the existence of a putative non-PCOS "female obesity-related secondary hypogonadism" (FOSH). We précis possible underlying mechanisms for the occurrence of hypogonadism in this context and consider how such mechanisms differ from MOSH in men, and from PCOS in women without obesity. In this review, we consider relevant etiological factors that are altered in obesity and that could impact on GnRH pulsatility to ascertain whether they could contribute to obesity-related secondary hypogonadism including: anti-Müllerian hormone, androgen, insulin, fatty acid, adiponectin, and leptin. More precise phenotyping of hypogonadism in women with obesity could provide further validation for non-PCOS FOSH and preface the ability to define/investigate such a condition.

Interpretation of Steroid Biomarkers in 21-Hydroxylase Deficiency and Their Use in Disease Management

The most common form of congenital adrenal hyperplasia is 21-hydroxylase deficiency (21OHD), which in the classic (severe) form occurs in roughly 1:16 000 newborns worldwide. Lifelong treatment consists of replacing cortisol and aldosterone deficiencies, and supraphysiological dosing schedules are typically employed to simultaneously attenuate production of adrenal-derived androgens. Glucocorticoid titration in 21OHD is challenging as it must balance the consequences of androgen excess vs those from chronic high glucocorticoid exposure, which are further complicated by interindividual variability in cortisol kinetics and glucocorticoid sensitivity. Clinical assessment and biochemical parameters are both used to guide therapy, but the specific purpose and goals of each biomarker vary with age and clinical context. Here we review the approach to medication titration for children and adults with classic 21OHD, with an emphasis on how to interpret adrenal biomarker values in guiding this process. In parallel, we illustrate how an understanding of the pathophysiologic and pharmacologic principles can be used to avoid and to correct complications of this disease and consequences of its management using existing treatment options.

Preterm infant circulating sex steroid levels are not altered by transfusion with adult male plasma: a retrospective multicentre cohort study

OBJECTIVE

To determine if plasma transfusions with male donor plasma to very preterm infants affect circulatory levels of sex steroids.

DESIGN AND PATIENTS

Retrospective multicentre cohort study in 19 infants born at gestational age <29 weeks requiring plasma transfusion during their first week of life.

SETTING

Three neonatal intensive care units in Sweden.

MAIN OUTCOME MEASURES

Concentrations of sex steroids and sex hormone-binding globulin (SHBG) in donor plasma and infant plasma measured before and after a plasma transfusion and at 6, 12, 24 and 72 hours.

RESULTS

The concentrations of progesterone, dehydroepiandrosterone and androstenedione were significantly lower in donor plasma than in infant plasma before the transfusion (median (Q1-Q3) 37.0 (37.0-37.0), 1918 (1325-2408) and 424 (303-534) vs 901 (599-1774), 4119 (2801-14 645) and 842 (443-1684) pg/mL), while oestrone and oestradiol were higher in donor plasma (17.4 (10.4-20.1) and 16.0 (11.7-17.2) vs 3.1 (1.1-10.2) and 0.25 (0.25-0.25) pg/mL). Median testosterone and dihydrotestosterone (DHT) levels were 116-fold and 21-fold higher in donor plasma than pre-transfusion levels in female infants, whereas the corresponding difference was not present in male infants. Plasma sex steroid levels were unchanged after completed transfusion compared with pre-transfusion levels, irrespective of the gender of the receiving infant. The SHBG concentration was significantly higher in donor than in recipient plasma (22.8 (17.1-33.5) vs 10.2 (9.1-12.3) nmol/L) before transfusion but did not change in the infants after the transfusion.

CONCLUSIONS

A single transfusion of adult male plasma to preterm infants had no impact on circulating sex steroid levels.

GWAS of three molecular traits highlights core genes and pathways alongside a highly polygenic background

Genome-wide association studies (GWAS) have been used to study the genetic basis of a wide variety of complex diseases and other traits. We describe UK Biobank GWAS results for three molecular traits-urate, IGF-1, and testosterone-with better-understood biology than most other complex traits. We find that many of the most significant hits are readily interpretable. We observe huge enrichment of associations near genes involved in the relevant biosynthesis, transport, or signaling pathways. We show how GWAS data illuminate the biology of each trait, including differences in testosterone regulation between females and males. At the same time, even these molecular traits are highly polygenic, with many thousands of variants spread across the genome contributing to trait variance. In summary, for these three molecular traits we identify strong enrichment of signal in putative core gene sets, even while most of the SNP-based heritability is driven by a massively polygenic background.

Pathological pulses in PCOS

Polycystic ovary syndrome (PCOS) is a highly prevalent endocrine disorder associated with hyperandrogenism and anovulation. Although a spectrum disorder, many women with PCOS exhibit elevated luteinizing hormone (LH) pulse frequency and an elevated LH to follicle stimulating hormone ratio. This aberrant pattern of gonadotrophin signalling drives many of the downstream ovarian features of PCOS, including increased androgen synthesis, and indicates neuroendocrine impairments upstream. Decreased responsiveness to gonadal steroid hormone negative feedback in PCOS patients points toward dysfunction within the gonadotropin-releasing hormone (GnRH) neuronal network in the brain. Excessive androgen exposure during development or over pubertal onset can recapitulate the neuroendocrine pathology of PCOS in pre-clinical models, and these models have been fundamental in beginning to pick apart the specific central mechanisms involved. This mini-review will briefly describe the pathology of PCOS associated with high frequency GnRH/LH pulses and then highlight what is currently known, and yet to be discovered, about the central mechanisms involved.

Effect of androgen on Kiss1 expression and luteinizing hormone release in female rats

Hyperandrogenic women have various grades of ovulatory dysfunction, which lead to infertility. The purpose of this study was to determine whether chronic exposure to androgen affects the expression of kisspeptin (ovulation and follicle development regulator) or release of luteinizing hormone (LH) in female rats. Weaned females were subcutaneously implanted with 90-day continuous-release pellets of 5α-dihydrotestosterone (DHT) and studied after 10 weeks of age. Number of Kiss1-expressing cells in both the anteroventral periventricular nucleus (AVPV) and arcuate nucleus (ARC) was significantly decreased in ovary-intact DHT rats. Further, an estradiol-induced LH surge was not detected in DHT rats, even though significant differences were not observed between DHT and non-DHT rats with regard to number of AVPV Kiss1-expressing cells or gonadotrophin-releasing hormone (GnRH)-immunoreactive (ir) cells in the presence of high estradiol. Kiss1-expressing and neurokinin B-ir cells were significantly decreased in the ARC of ovariectomized (OVX) DHT rats compared with OVX non-DHT rats; pulsatile LH secretion was also suppressed in these animals. Central injection of kisspeptin-10 or intravenous injection of a GnRH agonist did not affect the LH release in DHT rats. Notably, ARC Kiss1-expressing cells expressed androgen receptors (ARs) in female rats, whereas only a few Kiss1-expressing cells expressed ARs in the AVPV. Collectively, our results suggest excessive androgen suppresses LH surge and pulsatile LH secretion by inhibiting kisspeptin expression in the ARC and disruption at the pituitary level, whereas AVPV kisspeptin neurons appear to be directly unaffected by androgen. Hence, hyperandrogenemia may adversely affect ARC kisspeptin neurons, resulting in anovulation and menstrual irregularities.

The impact of genetic steroid disorders on human fertility

Human fertility requires an exquisitely complex orchestration of steroid hormone action to affect the necessary elements of reproduction, including folliculogenesis, endometrial advancement, ovulation, and implantation. Individuals affected by genetic steroid disorders often face substantial challenges to these crucial elements of fertility, in addition to the broader health implications of their diseases. In the following article, we review the impact of genetic steroid disorders on human reproduction, as well as the treatments, where available, aimed at circumventing such hurdles. Adrenal disorders will first be described, followed by rare gonadal steroid disorders.

Neuroendocrine causes of amenorrhea--an update

CONTEXT

Secondary amenorrhea--the absence of menses for three consecutive cycles--affects approximately 3-4% of reproductive age women, and infertility--the failure to conceive after 12 months of regular intercourse--affects approximately 6-10%. Neuroendocrine causes of amenorrhea and infertility, including functional hypothalamic amenorrhea and hyperprolactinemia, constitute a majority of these cases.

OBJECTIVE

In this review, we discuss the physiologic, pathologic, and iatrogenic causes of amenorrhea and infertility arising from perturbations in the hypothalamic-pituitary-adrenal axis, including potential genetic causes. We focus extensively on the hormonal mechanisms involved in disrupting the hypothalamic-pituitary-ovarian axis.

CONCLUSIONS

A thorough understanding of the neuroendocrine causes of amenorrhea and infertility is critical for properly assessing patients presenting with these complaints. Prompt evaluation and treatment are essential to prevent loss of bone mass due to hypoestrogenemia and/or to achieve the time-sensitive treatment goal of conception.

Characterizing the neuroendocrine and ovarian defects of androgen receptor-knockout female mice

Homozygous androgen receptor (AR)-knockout (ARKO) female mice are subfertile due to both intra- and extraovarian (neuroendocrine) defects as defined by ovary transplantation. Using ARKO mice, this study set out to reveal the precise AR-regulated pathways required for optimal androgen-regulated ovulation and fertility. ARKO females exhibit deficient neuroendocrine negative feedback, with a reduced serum luteinizing hormone (LH) response to ovariectomy (OVX) (P < 0.01). Positive feedback is also altered as intact ARKO females, at late proestrus, exhibit an often mistimed endogenous ovulatory LH surge. Furthermore, at late proestrus, intact ARKO females display diminished preovulatory serum estradiol (E2; P < 0.01) and LH (P < 0.05) surge levels and reduced Kiss1 mRNA expression in the anteroventral periventricular nucleus (P < 0.01) compared with controls. However, this reduced ovulatory LH response in intact ARKO females can be rescued by OVX and E2 priming or treatment with endogenous GnRH. These findings reveal that AR regulates the negative feedback response to E2, E2-positive feedback is compromised in ARKO mice, and AR-regulated negative and positive steroidal feedback pathways impact on intrahypothalamic control of the kisspeptin/GnRH/LH cascade. In addition, intraovarian AR-regulated pathways controlling antral to preovulatory follicle dynamics are disrupted because adult ARKO ovaries collected at proestrus have small antral follicles with reduced oocyte/follicle diameter ratios (P < 0.01) and increased proportions of unhealthy large antral follicles (P < 0.05) compared with controls. As a consequence of aberrant follicular growth patterns, proestrus ARKO ovaries also exhibit fewer preovulatory follicle (P < 0.05) and corpora lutea numbers (P < 0.01). However, embryo development to the blastocyst stage is unchanged in ARKO females, and hence, the subfertility is a consequence of reduced ovulations and not altered embryo quality. These findings reveal that the AR has a functional role in neuroendocrine regulation and timing of the ovulatory LH surge as well as antral/preovulatory follicle development.

Pharmacokinetics and Acute Safety of Inhaled Testosterone in Postmenopausal Women

This was a preliminary feasibility study to assess the pharmacokinetics and acute safety of a single dose of orally inhaled testosterone via the AERx system, a novel handheld aerosol delivery system in postmenopausal women. Twelve postmenopausal women stabilized on oral estrogen therapy were treated with a single dose of testosterone (0.1, 0.2, or 0.3 mg) by inhalation. Plasma concentrations of sex steroids were measured between 1 and 360 minutes. Pulmonary and cardiovascular adverse events were monitored. Inhaled testosterone produced a dose-dependent increase in plasma total and free testosterone. At the highest dose (0.3 mg), total and free testosterone increased from baseline (mean +/- SD, 0.6 +/- 0.3 nmol/L, 2.5 +/- 1.0 pmol/L) to maximum levels of 62.6 +/- 20.4 nmol/L (total) and 168.2 +/- 50.2 pmol/L(free), occurring 1 to 2 minutes after dosing. A 2-compartment model best described the free and total testosterone pharmacokinetic profile. Dihydrotestosterone levels were higher than baseline at 60 minutes (P < .0002). Estradiol did not vary, but sex hormone binding globulin and albumin fell. There were no adverse events related to the treatment. Administration of inhaled testosterone is safe and achieves a supraphysiologic "pulse" kinetic profile of total and free testosterone with a rapid return to pretreatment levels.

Targeted loss of androgen receptor signaling in murine granulosa cells of preantral and antral follicles causes female subfertility

Ovarian granulosa cells display strong androgen receptor (AR) expression, suggesting a functional role for direct AR-mediated actions within developing mammalian follicles. By crossing AR-floxed and anti-Müllerian hormone (AMH)-Cre recombinase mice, we generated granulosa cell-specific androgen receptor knockout mice (GCARKO). Cre expression, assessed by lacZ activity, localized to 70%-100% of granulosa cells in most preantral to antral follicles, allowing for selected evaluation of granulosa cell AR-dependent actions during follicle development. Relative to wild-type (WT) females, GCARKO females were subfertile, producing a 24% reduction in the number of litters (P < 0.05) over 6 mo and an age-dependent decrease in total number of pups born, evident from 6 mo of age (P < 0.05). Follicle dynamics were altered in GCARKO ovaries at 3 mo of age, with a significant reduction in large preantral and small antral follicle numbers compared to WT ovaries (P < 0.05). Global premature follicle depletion was not observed, but increased follicular atresia was evident in GCARKO ovaries at 6 mo of age, with an 81% increase in unhealthy follicles and zona pellucida remnants (P < 0.01). Cumulus cell expansion was decreased (P < 0.01) and oocyte viability was diminished in GCARKO females, with a significant reduction in the percentage of oocytes fertilized after natural mating and, thus, in the rate of progression to the two-cell embryo stage (P < 0.05). In addition, compared with age-matched WT females, 6-mo-old GCARKO females exhibited significantly prolonged estrous cycles (P ≤ 0.05), suggesting altered hypothalamic-pituitary-gonadal feedback signaling. In conclusion, our findings revealed that selective loss of granulosa cell AR actions during preantral and antral stages of development leads to a premature reduction in female fecundity through reduced follicle health and oocyte viability.

Influence of hormonal control on LH pulsatility and secretion in women with classical congenital adrenal hyperplasia

OBJECTIVE

Women with classical congenital adrenal hyperplasia (CAH) exhibit reduced fertility due to several factors including anovulation. This has been attributed to a disturbed gonadotropic axis as in polycystic ovary syndrome (PCOS), but there is no precise evaluation. Our aim was to evaluate the gonadotropic axis and LH pulsatility patterns and to determine factor(s) that could account for the potential abnormality of LH pulsatility.

DESIGN

Case/control study.

METHODS

Sixteen CAH women (11 with the salt-wasting form and five with the simple virilizing form), aged from 18 to 40 years, and 16 age-matched women, with regular menstrual cycles (28 ± 3 days), were included. LH pulse patterns over 6 h were determined in patients and controls.

RESULTS

No differences were observed between patients and controls in terms of mean LH levels, LH pulse amplitude, or LH frequency. In CAH patients, LH pulsatility patterns were heterogeneous, leading us to perform a clustering analysis of LH data, resulting in a two-cluster partition. Patients in cluster 1 had similar LH pulsatility patterns to the controls. Patients in cluster 2 had: lower LH pulse amplitude and frequency and presented menstrual cycle disturbances more frequently; higher 17-OH progesterone, testosterone, progesterone, and androstenedione levels; and lower FSH levels.

CONCLUSIONS

LH pulsatility may be normal in CAH women well controlled by hormonal treatment. Undertreatment is responsible for hypogonadotropic hypogonadism, with low LH pulse levels and frequency, but not PCOS. Suppression of progesterone and androgen concentrations during the follicular phase of the menstrual cycle should be a major objective in these patients.

Evidence that obesity and androgens have independent and opposing effects on gonadotropin production from puberty to maturity

Optimal fat mass is necessary for normal gonadotropin levels in adults, and both undernutrition and overnutrition suppress gonadotropins: thus, the gonadotropin response to relative adipose mass is biphasic. Adult obesity is associated with blunted luteinizing hormone (LH) pulse amplitude that is partially attributable to increased LH clearance rate. Testosterone appears to have a biphasic effect on gonadotropin production in females. Moderate elevations of testosterone appear to stimulate LH production at both the hypothalamic and pituitary level, while very high levels of testosterone suppress LH. Thus, obesity per se appears to suppress gonadotropin production, and moderate hyperandrogenemia in women appears to stimulate LH. The ordinary hypergonadotropic hyperandrogenism of obese women appears to be an exception to this model because it is usually due to polycystic ovary syndrome (PCOS), a condition in which intrinsic functional ovarian hyperandrogenism and excess adiposity share a common origin that involves insulin-resistant hyperinsulinemia. LH elevation seems to be secondary to hyperandrogenemia and is absent in the most obese cases. Overweight early pubertal girls have significant blunting of sleep-related LH production, which is the first hormonal change of puberty. The data are compatible with the possibility that excess adiposity may paradoxically subtly suppress hypothalamic-pituitary-gonadal function in early puberty although it is known to contribute to the early onset of puberty.

Acute effects of testosterone infusion on the serum luteinizing hormone profile in eumenorrheic and polycystic ovary syndrome adolescents

CONTEXT

Little is known about the neuroendocrine effects of androgens on the GnRH-LH unit in females.

OBJECTIVE

Our objective was to evaluate androgen negative feedback on the GnRH-LH axis in eumenorrheic and polycystic ovary syndrome (PCOS) adolescents.

DESIGN AND SETTING

We conducted a prospective, longitudinal, randomized, double-blind study at a pediatric endocrinology clinical research center.

PARTICIPANTS

Seven nonobese PCOS adolescents and seven matched controls (C) were studied in the early follicular phase of three consecutive menstrual cycles or in three consecutive months.

INTERVENTION

Pulsatile LH release was determined during saline [baseline (B)] and constant testosterone (T) infusions: low dose (T-LD) 0.75 and high dose (T-HD) 2.5 mg/12 h iv. Blood samples were drawn every 20 min overnight.

MAIN OUTCOME MEASURES

LH (immunofluorometric assay) and T (electrochemiluminescence immunoassay) were determined at B, and during both T-LD and T-HD. LH profiles were analyzed by deconvolution and approximate entropy analyses.

RESULTS

On T-LD, C and PCOS serum T levels increased 2- to 3-fold vs. B. On T-HD, T values doubled in both groups vs. T-LD. Controls on T-LD had greater 12-h pulsatile LH secretion rate (P < 0.05 vs. B) and on T-HD had lower mean, pulsatile, basal LH release and LH approximate entropy (vs. B, P < 0.05). PCOS did not respond to T-LD. High-dose T did not alter mean LH in PCOS but increased pulsatile and reduced basal LH secretion.

CONCLUSIONS

PCOS adolescents have impaired suppression of pulsatile LH secretion rate consistent with reduced androgen negative feedback. Attenuation of T feedback in nonobese adolescents with PCOS extends the pathophysiology of this syndrome.

Subfertile female androgen receptor knockout mice exhibit defects in neuroendocrine signaling, intraovarian function, and uterine development but not uterine function

Female androgen receptor (AR) knockout mice (AR(-/-)) generated by an in-frame Ar exon 3 deletion are subfertile, but the mechanism is not clearly defined. To distinguish between extra- and intraovarian defects, reciprocal ovarian transplants were undertaken. Ovariectomized AR(-/-) hosts with wild-type (AR(+/+)) ovary transplants displayed abnormal estrus cycles, with longer cycles (50%, P < 0.05), and 66% were infertile (P < 0.05), whereas AR(+/+) hosts with either AR(-/-) or surgical control AR(+/+) ovary transplants displayed normal estrus cycles and fertility. These data imply a neuroendocrine defect, which is further supported by increased FSH (P <0.05) and estradiol (P <0.05), and greater LH suppressibility by estradiol in AR(-/-) females at estrus (P <0.05). Additional intraovarian defects were observed by the finding that both experimental transplant groups exhibited significantly reduced pups per litter (P < 0.05) and corpora lutea numbers (P < 0.05) compared with surgical controls. All groups exhibited normal uterine and lactation functions. AR(-/-) uteri were morphologically different from AR(+/+) with an increase in horn length (P < 0.01) but a reduction in uterine diameter (P < 0.05), total uterine area (P < 0.05), endometrial area (P < 0.05), and myometrial area (P < 0.01) at diestrus, indicating a role for AR in uterine growth and development. Both experimental transplant groups displayed a significant reduction in uterine diameter (P < 0.01) compared with transplanted wild-type controls, indicating a role for both AR-mediated intraovarian and intrauterine influences on uterine physiology. In conclusion, these data provide direct evidence that extraovarian neuroendocrine, but not uterine effects, as well as local intraovarian AR-mediated actions are important in maintaining female fertility, and a disruption of AR signaling leads to altered uterine development.

Luteinizing hormone pulsatility in patients with major ovarian hyperandrogenism

Hyperandrogenism and ovulatory dysfunction are common in women with either polycystic ovary (PCOS) or ovarian virilizing tumor. However, contrasting with the numerous studies that have extensively described gonadotropin secretory abnormalities, principally increased LH pulse amplitude and frequency, few studies have concerned gonadotropin secretion in patients with ovarian virilizing tumors; low gonadotropin levels have occasionally been reported, but never extensively studied. The goal of the present study was to further evaluate the pulsatility of LH secretion in women with ovarian virilizing tumor compared with that of PCOS patients. Eighteen women with major hyperandrogenism (plasma testosterone level >1.2 ng/ml) were studied (5 women with ovarian virilizing tumor, 13 women with PCOS, and 10 control women). Mean plasma LH level, LH pulse number and amplitude were dramatically low in patients with ovarian tumors when compared to both PCOS (p<0.001) and controls (p<0.001). In case of major hyperandrogenism, LH pulse pattern differs markedly between women with ovarian virilizing tumor or PCOS, suggesting different mechanisms of hypothalamic or pituitary feedback.

Effects of chronic hyperandrogenism and/or administered central nervous system insulin on ovarian manifestation and gonadotropin and steroid secretion

OBJECTIVE

Polycystic ovarian syndrome is characterized by hyperandrogenism and insulin resistance. We studied the effects of central hyperinsulinemia and peripheral hyperandrogenism on gonadotropin secretion, steroid secretion, and ovarian histology in female rats.

DESIGN

Experimental in vivo animal study.

SETTING

University research center.

ANIMAL(S)

250-300 g female Wistar rats.

INTERVENTION(S)

Insertion of testosterone pellets and/or administration of intracerebroventricular (ICV) insulin.

MAIN OUTCOME MEASURE(S)

Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels before and after GnRH administration; testosterone, insulin, and glucose levels; and ovarian histology.

RESULT(S)

Compared with control, rats with testosterone implant had a lower LH and higher FSH while rats with testosterone plus insulin had a higher FSH. Intracerebroventricular (ICV) insulin alone increased LH in response to GnRH. Ovarian histology indicated that testosterone-implanted rats had larger ovaries and an increased number of cystic follicles >50 microm as well as substantial theca enlargement. The administration of testosterone did not alter serum insulin, and ICV insulin did not increase testosterone levels.

CONCLUSION(S)

We suggest that ICV insulin acts either directly or indirectly to increase the LH responsiveness to GnRH. ICV insulin arrested the maturation of follicles leading to an increase in the number of small follicles. Peripheral androgens stimulated theca enlargement with cystic follicles. The combination of ICV insulin and peripheral androgens attenuated ovarian histologic changes and gonadotropin secretion. Thus, central hyperinsulinemia and peripheral hyperandrogenism may play a role in gonadotropin secretion as well as ovarian morphology.

Relationship of GnRH-stimulated LH release to episodic LH secretion and baseline endocrine-metabolic measures in women with polycystic ovary syndrome

BACKGROUND AND OBJECTIVE

In polycystic ovary syndrome (PCOS) inappropriate gonadotrophin secretion is characterized by increased pulse frequency and amplitude, elevated 24-h mean serum concentrations, and greater responses to GnRH. While the mechanism(s) responsible for this increased release of LH are not well understood, enhanced LH secretion has been attributed to increased pituitary sensitivity to GnRH and feedback influences from circulating steroid hormones. To address these considerations, we conducted a study to examine the relationships between GnRH-stimulated LH responses, episodic gonadotrophin secretion, and baseline measurements of endocrine-metabolic function in PCOS.

PATIENTS

Serum LH responses to sequential multidose GnRH administration and pulsatile gonadotrophin secretion were examined in 13 PCOS and 13 normal women.

MEASUREMENTS

Serum LH, steroid hormone, insulin and glucose levels were determined in blood samples obtained during assessment of episodic gonadotrophin secretion and LH responses to GnRH stimulation.

DESIGN

Each subject was studied on two consecutive days. On study day 1 each subject underwent frequent blood sampling every 10 min for 12 h. On study day 2 each received sequential doses of GnRH, 2 microg, 10 microg and 20 microg, administered intravenously at 4-h intervals over a continuous 12-h period.

RESULTS

Serum LH responses following GnRH were markedly greater in PCOS compared to normal women, as expected. In individual PCOS, peak LH responses to GnRH were significantly correlated with corresponding basal LH and LH pulse amplitude, but not LH pulse frequency. In the PCOS group, LH responses were positively correlated with serum oestradiol (E2) and inversely related to body mass index (BMI). Between-group differences in LH responsiveness disappeared when controlling for serum testosterone (T) levels.

CONCLUSIONS

These results indicate that the absolute LH increment following GnRH is largely dependent on baseline LH levels and may account for the well-documented difference in LH responsiveness between PCOS and normal women. That neither LH responses to GnRH nor LH pulse amplitude were correlated to LH pulse frequency suggests involvement of other factors along with GnRH to account for increased LH secretion in PCOS. In addition to E2 and BMI, serum testosterone appears to be, at least in part, responsible for differences in LH secretion and release between PCOS and normal women.

Androgen production in women

OBJECTIVE

To describe the sources, production rates, circulating concentrations, and regulatory mechanisms of the major androgen precursors and androgens in women.

DESIGN

Review of the major published literature.

RESULT(S)

Quantitatively, women secrete greater amounts of androgen than of estrogen. The major circulating steroids generally classified as androgens include dehydroepiandrosterone sulphate (DHEAS), dehydroepiandrosterone (DHEA), androstenedione (A), testosterone (T), and dihydrotestosterone in descending order of serum concentration, though only the latter two bind the androgen receptor. The other three steroids are better considered as pro-androgens. Dehydroepiandrosterone is primarily an adrenal product, regulated by adrenocorticotropic hormone (ACTH) and acting as a precursor for the peripheral synthesis of more potent androgens. Dehydroepiandrosterone is produced by both the ovary and adrenal, as well as being derived from circulating DHEAS. Androstenedione and testosterone are products of the ovary and the adrenal. Testosterone circulates both in its free form, and bound to protein including albumin and sex steroid hormone-binding globulin (SHBG), the levels of which are an important determinant of free testosterone concentration.

CONCLUSION(S)

The postmenopausal ovary is an androgen-secreting organ and the levels of testosterone are not directly influenced by the menopausal transition or the occurrence of menopause. Dihydrotestosterone (DHT) is primarily a peripheral product of testosterone metabolism. Severe androgen deficiency occurs in hypopituitarism, but other causes may lead to androgen deficiency, including Addison's disease, corticosteroid therapy, chronic illness, estrogen replacement (leads to elevated SHBG and, therefore, low free testosterone), premenopausal ovarian failure, or oophorectomy.

Mechanisms of hypothalamic-pituitary-gonadal disruption in polycystic ovarian syndrome

Although the pathogenesis of polycystic ovarian syndrome (PCOS) is still controversial, a series of investigations has demonstrated an array of neuroendocrine abnormalities as a major component of the syndrome. From a neuroendocrine perspective, patients with PCOS exhibit an accelerated frequency and/or higher amplitude of LH pulses, augmentation of LH secretory burst mass, and a more disorderly LH release. Elevated in vitro LH bioactivity and a preponderance of basic LH isoforms, which correlate positively with elevated serum 17-hydroxyprogesterone, androstenedione, and testosterone concentrations, also characterize adolescents with PCOS. Heightened GnRH drive of gonadotropin secretion and a steroid-permissive milieu appear to jointly promote elevated secretion of basic LH isoforms. Positive feedback is implied, because hypersecretion of highly bioactive LH in PCOS probably contributes to inordinate androgen output. However, the precise nature of feedback disruption remains uncertain. Indeed, recent data suggest that PCOS is marked by anomalies of both feedforward and feedback signaling between GnRH/LH and ovarian androgens. From a single hormone perspective, the individual patterns of LH and androstenedione release are consistently more irregular in patients with PCOS. Bihormonal analysis has disclosed concomitant uncoupling of the pairwise synchrony of LH and testosterone, LH and androstenedione, and testosterone and androstenedione secretion. The foregoing ensemble of findings points to deterioration of both orderly uniglandular and coordinate bihormonal output in PCOS. Additional studies are needed to establish the primary pathophysiologic mechanisms underlying this disorder.

The effect of pharmacokinetically guided acute intravenous testosterone administration on electrocardiographic and blood pressure variables

Previous studies have demonstrated that intravenous testosterone can dilate coronary arteries and increase exercise treadmill time, but the electrocardiographic and hemodynamic effects are unknown. This trial determined the hemodynamic and electrocardiographic effects of dosing intravenous testosterone to achieve a physiologic and a superphysiologic serum testosterone concentration. Twenty men (70.6 +/- 6.2 years) had individualized testosterone bolus and continuous infusions designed to increase the serum testosterone concentration by two (physiologic) and six times baseline (superphysiologic). The men were studied on three occasions when they were randomly allocated to received a placebo, physiologic testosterone regimen, or superphysiologic testosterone regimen. Blood pressures and 12-lead electrocardiograms (ECGs) were taken preinfusion and 28 minutes after initiating the infusion on each visit. The blood pressure (systolic and diastolic) and ECG variables (PR, QRS, QT, QTc, and RR intervals) preinfusion and during the infusion were compared, and the delta changes in the variables were compared between groups. The physiologic testosterone regimen increased the serum testosterone concentration by 2.39 +/- 0.48 times the preinfusion concentration, while the superphysiologic regimen increased it by 6.22 +/- 0.99 times. No significant changes occurred in the blood pressure or ECG variables in any group versus preinfusion values or between the three groups. Exogenously administered intravenous testosterone does not significantly affect the blood pressure or ECG variables when given to achieve physiologic or superphysiologic concentrations.

Neuroendocrine aspects of polycystic ovary syndrome

A series of investigations have emphasized the heterogeneous nature of the clinical condition known as PCOS and have delineated several factors that may contribute to the hyperandrogenemia and anovulation in this condition. Currently, it remains unclear whether intrinsic abnormalities of ovarian steroidogenesis, the effects of hyperinsulinemia in augmenting LH stimulation of ovarian androgen production, and the persistent rapid frequency of LH/GnRH secretion are primary factors in all patients. Indeed, these factors may have variable roles in different patients, all of whom present with the clinical syndrome of PCOS. A consensus has emerged that abnormalities in the neuroendocrine control of GnRH secretion exist in a significant subset of patients and lead to persistent hypersecretion of LH, which seems to be an important component of the syndrome, particularly in nonobese patients. The relative frequency of primary abnormalities in the regulation of GnRH secretion versus secondary changes reflecting altered circulating concentrations of ovarian steroid remains uncertain. No clear evidence exists for an underlying neuroendocrine abnormality of GnRH regulation in all patients. The recent data showing insensitivity of the hypothalamic GnRH pulse generator to E2 progesterone feedback have suggested potential mechanisms that may explain the abnormalities of GnRH secretion seen in adolescent girls in whom the clinical syndrome of PCOS is destined to develop. Further studies are required in adolescents to establish whether GnRH regulation is impaired during puberty or whether data in adults simply reflect the long-term effects of elevated androgens, estrogens, or other hormones on the hypothalamus. Studies in carefully delineated subgroups of patients with PCOS are needed to establish these points, with a long-term goal of providing patients with improved methods of inducing ovulation and reducing hyperandrogenemia.

Insights into hypothalamic-pituitary dysfunction in polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is characterized by menstrual dysfunction and hyperandrogenism in the absence of other known causes. While the pathogenesis of PCOS remains elusive and is likely to involve abnormalities in several systems, there has long been an association of abnormal gonadotropin secretion with this disorder. In recent studies we have determined that 94% of women meeting the broad criteria for PCOS have an increased LH/FSH ratio. Several lines of evidence suggest that the mechanisms underlying the increased LH/FSH ratio in PCOS include an increased frequency of GnRH secretion. Decreased sensitivity to progesterone negative feedback on the GnRH pulse generator may play a role in this neuroendocrine defect. Additional factors which may contribute to the low to normal FSH levels in the face of increased LH include chronic mild estrogen increases and possibly inhibin. In addition to these effects on the differential control of FSH, there is increased pituitary sensitivity of LH secretion to GnRH. Both estrogen and androgens have been proposed as candidates mediating these effects. Superimposed on these underlying abnormalities in gonadotropin secretion is a marked inhibitory effect of obesity on LH secretion which may be mediated at either a pituitary or hypothalamic level.

Neuroendocrinology of the polycystic ovary syndrome

The clinical and biochemical heterogeneity of the PCOS is mirrored by the range of neuroendocrine disturbances described in women with PCOS. An increased serum LH concentration is a common, although not ubiquitous, feature and occurs primarily as a result of an increase in the amplitude of pulsatile LH, and presumably GnRH, secretion. The frequency of pulsatile GnRH secretion may, however, be increased in certain patients and may conceivably increase LH bioactivity by altering glycosylation of the molecule. Vigorous debate continues as to whether the observed changes in gonadotrophins are a primary abnormality or occur secondary to alterations in peripheral steroid concentrations. The proponents of the frequency hypothesis point to the discordant changes in gonadotrophin secretion that may be induced by rapid frequency exogenous GnRH stimulation in patients with hypogonadotrophic hypogonadism. Those who believe that the inappropriate gonadotrophin secretion is a secondary phenomenon argue that manipulation of peripheral steroid levels, by either administration of oestrogen/progesterone, induced ovulation or ovarian diathermy, may correct the disturbance of gonadotrophin secretion, which is therefore presumably a consequence of changes in ovarian steroid feedback signals. The weight of evidence at present suggests that the inappropriate gonadotrophin secretion is usually a secondary abnormality, although there may be groups of patients with a primary increase in GnRH pulsatility. The search for a unifying neuroendocrine disturbance in PCOS has been frustrated by the inability to find consistent evidence of disordered central dopaminergic, opioidergic, noradrenergic or serotoninergic pathways. Those abnormalities which have been uncovered appear to be secondary to chronic anovulation rather than of primary pathological import, and emphasize the central importance of the ovary as culprit rather than victim in PCOS.

Patterns of luteinizing and follicle-stimulating hormone pulsatility in menopausal women: correlation with plasma testosterone level and vasomotor instability episodes

OBJECTIVE

The purpose of this study was to test the hypothesis that subtle differences among postmenopausal women can be detected by careful analysis of plasma luteinizing hormone and follicle-stimulating hormone pulses.

STUDY DESIGN

Twelve postmenopausal women not receiving estrogen therapy were admitted for continuous blood withdrawal at the rate of 1 ml/min. Aliquots of 3 ml of pooled blood were collected every 3 minutes for 3 hours for the measurement of plasma luteinizing hormone and follicle-stimulating hormone. Estradiol, estrone, free testosterone, androstenedione, and dihydrotestosterone were measured from pooled specimens. Concomitantly, continuous recordings of peripheral blood flow and peripheral temperature from the opposite arm were obtained to detect vasomotor instability episodes.

RESULTS

Analysis of gonadotropin pulses revealed a single pattern of plasma follicle-stimulating hormone but two distinct patterns of luteinizing hormone frequency and amplitude. One group of six women had a low mean (+/- SEM) interpulse interval frequency of 0.8 +/- 0.26 (p < 0.005) and a high mean amplitude of 18.4 +/- 1.8 IU/L (p < 0.05). The second group of six women had a high mean interpulse interval frequency of 3.5 +/- 0.34 and a low mean amplitude of 12.2 +/- 1.8 IU/L luteinizing hormone pulses. Women with this pattern had more inter-vasomotor instability episode intervals (3.5 +/- 1.6) than did women with low frequency and high amplitude (1.3 +/- 0.5, p < 0.001). Women with low frequency and high amplitude pulses had higher plasma levels of estrone (266 +/- 33 nmol/L), testosterone (2.3 +/- 0.7 mmol/L), and free testosterone (8.0 +/- 0.1 pmol/L, p < 0.05).

CONCLUSION

There are subgroups of postmenopausal women with different patterns of luteinizing hormone pulsatility. This difference can be explained by higher steroid levels in women with low frequency and high amplitude pulses.

Role of androgens in the regulation of the human menstrual cycle

Although previous investigations have examined the importance of androgens in the regulation of the human menstrual cycle, no consensus has been reached, due to conflicting results. We have therefore used the non-steroidal anti-androgen flutamide as a pharmacological probe to evaluate the role of androgens in the control of gonadotropin secretion in normally cycling women. Eight women were studied during control and treatment cycles, during which either placebo (as control) or flutamide (750 mg orally) was given daily. Blood was sampled every other day during the follicular and luteal phases and daily around the expected midcycles for determination of luteinizing hormone (LH), follicle stimulating hormone (FSH), estradiol, progesterone and androgens (testosterone, androstenedione, dehydroepiandrosterone sulfate) by radioimmunoassay and immunoradiometric assay. To establish unstimulated and gonadotropin releasing hormone (GnRH)-stimulated gonadotropin profiles, blood samples were frequently collected (every 10 min for 8 h, GnRH 25 micrograms i.v. after 7 h on day 10 in both the control and treatment cycles. Compared to control conditions, the durations of both the follicular and luteal phases did not change considerably during flutamide treatments. Serum androgen levels (testosterone, androstenedione, dehydroepiandrosterone sulfate) were significantly (p < 0.01) reduced during androgen antagonism. Daily gonadotropin and estradiol levels did not differ between control and flutamide cycles, while progesterone secretion tended to be attenuated (p = 0.2) during the luteal phases of the flutamide cycles. The LH and FSH secretory profiles and the GnRH-stimulated gonadotropin responses remained virtually unchanged during androgen antagonism.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical implications of hyperinsulinaemia in women

In the polycystic ovary syndrome, hyperinsulinaemia is commonly found in women with hirsutism, oligomenorrhoea and acanthosis nigricans and this subset of patients possess adverse risk factors for coronary artery disease, particularly reduced HDL2 concentrations. Conversely, raised serum insulin concentrations are not common in women with PCOS in whom raised serum LH concentrations or regular menstrual cycles are present. We postulate that both direct ovarian and indirect actions of insulin (through changes in IGFI-I, IGFBP-I and SHBG concentrations) play important roles in determining androgen concentrations in women. Many intriguing questions follow from this link between the control of nutrition and reproduction and many old observations required re-examination in this new light. Vital to our understanding in this field will be the cause of moderate hyperinsulinaemia, the action of insulin on the normal ovary, and the importance of adverse surrogate risk factors for heart disease in hyperinsulinaemic women.

Gonadotropin-releasing hormone agonist as a probe for the pathogenesis and diagnosis of ovarian hyperandrogenism

We have found that women with typical polycystic ovary syndrome have supranormal plasma 17-hydroxyprogesterone responses to a 100-micrograms test dose of the gonadotropin-releasing hormone agonist nafarelin without evidence of hindered estrogen secretion. To understand the basis of this response, we computed the apparent efficiency of the steps in steroid biosynthesis from the pattern of plasma steroids in response to nafarelin. The proximate cause appears to be excessive 17 alpha-hydroxylase activity and high, yet partially down-regulated, 17,20-lyase activity in the delta 4-pathway. These results suggest that this pattern of steroid secretion results from abnormal regulation (dysregulation) of these activities, possibly involving the enzyme cytochrome P450c17. To determine the usefulness of nafarelin testing for the diagnosis of ovarian hyperandrogenism, we then prospectively studied 40 hyperandrogenic women. The plasma 17-PROG response to nafarelin was supranormal in 58% of the women. The responses of 17-PROG to nafarelin and free testosterone to dexamethasone correlated well and were concordant in approximately 85% of cases. Baseline serum luteinizing hormone concentration was elevated in only 48% of cases. To understand ovarian structure-function relationships, we studied another 20 consecutive hyperandrogenic women. Among seven women with polycystic ovaries, five had an elevated LH level, and four of these five (80%) had an elevated 17-PROG response to nafarelin. Conversely, about half of patients with the PCOS-like disorder of ovarian function did not have polycystic ovaries. Ovarian stromal area, but not LH levels, correlated significantly (r = 0.45) with the 17-PROG response to nafarelin. Thus, both stromal hyperplasia and dysregulation of steroidogenesis seem to be manifestations of abnormal intraovarian regulation of cell growth and function. We conclude that a PCOS-like disorder of ovarian function in response to nafarelin testing is found in approximately half of hyperandrogenic women. The pathogenetic implication of our results is that abnormal intraovarian modulation of LH action seems to be a major factor in ovarian hyperandrogenism. The diagnostic implication of our data is that ovarian androgen excess will often be missed by use of common diagnostic criteria for PCOS.

How do androgens affect episodic gonadotrophin secretion in postmenopausal women?

In the absence of any significant ovarian oestrogen secretion, as in post-menopausal women, the hypothalamic-pituitary axis may still be influenced by the androgens which continue to be produced. The episodic secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) by postmenopausal women was accordingly assessed following short-term androgen antagonism induced by flutamide, a specific androgen receptor blocker. Blood samples were collected at 10-min intervals for 10 h in nine women before and during flutamide administration (750 mg/day for 6 days) for the determination of gonadotrophin and sex hormone concentrations by radioimmunoassay. On both occasions, 25 micrograms of gonadotrophin-releasing-hormone (GnRH) was injected intravenously 8 h after initiation of the blood collections. Flutamide administration decreased (P less than 0.01 or less) androgen concentrations (testosterone, androstenedione and dehydroepiandrosterone sulphate) in relation to baseline values, but did not alter oestrogen (oestrone and oestradiol) or sex-hormone-binding globulin levels. The LH and FSH pulse characteristics (frequency, amplitude, interpulse interval and transverse mean levels) determined by a cluster algorithm in the gonadotrophin secretory profiles did not differ before and during androgen blockade. By contrast, androgen antagonism increased LH (P less than 0.01) and tended to enhance FSH (P = 0.10) FSH release in response to GnRH stimulation. Hence, short-term androgen receptor blockade with flutamide did not greatly affect episodic gonadotrophin secretion. However, the combined evidence of the enhanced gonadotrophin release observed in response to GnRH stimulation and the unchanged gonadotrophin secretion during androgen antagonism suggests that alterations in the magnitude, but not the frequency, of hypothalamic GnRH release had occurred. Even in the presence of substantial serum androgen concentrations, the gonadotrophin pulse rhythm in hypogonadal women constitutes the maximal-rate GnRH-LH release pattern.

The impact of ovarian laser surgery on the gonadotrophin secretion in women with polycystic ovarian disease

To evaluate the effects of ovarian surgery on the deranged episodic gonadotrophin release of women with the polycystic ovarian disease (PCOD), we studied 11 patients with the clinical and endocrinological features of PCOD before and after laparoscopic laser coagulations of ovarian surfaces and cysts. During both occasions, blood was collected at 15-min intervals for 8 h to determine LH and FSH secretory profiles and additionally for 3 h during GnRH injections (25 micrograms twice within 2 h) to assess pituitary responsiveness. Serum testosterone, androstendione and oestrogen (oestrone, oestradiol) levels were markedly reduced (P less than 0.05 or less) after surgery. Mean LH concentrations declined (P less than 0.001), while FSH levels increased (P less than 0.01) following laser treatments. The LH pulse frequencies (by Cluster analysis) did not change after ovarian surgery, but the LH pulse amplitudes were markedly reduced (P less than 0.01). Lower (P less than 0.05 or less) LH concentrations were attained in response to GnRH challenges, and the stimulated FSH release also tended to decrease after laser treatments. Thus, ovarian surgery in PCOD women resulted in reduced serum sex steroid concentrations and in divergent effects on serum LH and FSH levels. The attenuated pituitary LH responsiveness after ovarian surgery suggests action of sex steroids primarily at the pituitary site, while the increase in FSH concentrations may be attributed to other factors selectively modulating FSH release.

Postmenopausal androgen secreting ovarian tumour: pathophysiological implications; a case report

Hyperandrogenism in women is usually accompanied by a disruption of the hypothalamic-pituitary-ovarian axis; however, the precise effect of chronically elevated androgens on this axis is poorly understood. We report a postmenopausal woman with a virilizing ovarian tumour in whom the effects of chronic testosterone secretion on the hypothalamic-pituitary axis was investigated. A 56-year-old woman was evaluated for hirsutism and hyperandrogenism of recent onset. Peripheral serum testosterone was high (19.4 nmol/l), while gonadotropins were below normal for a postmenopausal woman, FSH (19.7 IU/l) being higher than LH (10.3 IU/l). Four LH and 1 FSH pulse were detected over 4 h. A left intraovarian testosterone secreting tumour, shown by catheterization of the ovarian veins and containing imperfect crystalloids of Reinke, was excised. Postoperatively, peripheral testosterone became undetectable, while gonadotropins rose to normal postmenopausal values. This patient's LH/FSH ratio was less than 1, in contrast with other situations of chronic hyperandrogenism. This could be explained by the concomitant hypoestrogenic state, and/or the theoretical absence of inhibin. The interest of this case resides in that it constitutes an appropriate model for studying the effects of testosterone on LH and FSH secretion in the absence of the other two classically involved modulators, namely oestrogens and inhibin.

Ovarian regulation of pulsatile luteinizing hormone secretion during late gestation in the rat*

Abstract The object of this study was to examine the influence of both estradiol (E(2)) and progesterone (P) alone or in combination on luteinizing hormone (LH) pulse amplitude and frequency during the interval between Days 21 and 22 of gestation. This was done by analyzing pulsatile LH release in rats bled on Days 21 and 22 of gestation, and in animals ovariectomized (OVX) on Day 21, implanted with silastic capsules producing plasma levels of E(2) and/or P characteristic of the Day 21 to 22 interval, and bled on Day 22 Pulsatile LH release increased between Days 21 and 22 due to an increase in pulse frequency and a small elevation in pulse amplitude. OVX produced no further increase in pulse frequency but markedly enhanced the small change in pulse amplitude. Preventing either the decline in plasma P that normally occurs between Days 21 and 22, or just the small additional decrease in plasma P levels produced by OVX, had no suppressive effect on pulse amplitude or frequency, although Day 22 levels of P alone augmented the normal increase in pulse frequency occurring between Days 21 and 22. Restoration of physiological plasma E(2) levels had no effect on the normal increase in pulse frequency, but partially attenuated the OVX-induced increase in pulse amplitude. Replacement of physiological Day 22 levels of both E(2) and P also decreased LH pulse amplitude, although amplitude was not significantly different from that seen following E(2) replacement alone, and was still greater than the normal Day 22 value. In contrast, restoration of physiological plasma levels of E(2)+ P caused a suppression of LH pulse frequency below that normally seen on Day 22. While E(2)+ P did not completely prevent the OVX-induced increase in pulse amplitude, administration of charcoal-extracted porcine follicular fluid to rats OVX on Day 21, and in which physiological plasma levels of E(2)+ P were restored, caused a further reduction in pulse amplitude. These data demonstrate that 1) marked increases in LH pulse amplitude are prevented from occurring between Days 21 and 22 of gestation by ovarian steroids, notably E(2), and that this suppression is enhanced by a non-steroidal factor present in porcine follicular fluid, 2) neither E(2) or P alone suppresses LH pulse frequency on Day 22 of gestation; LH pulse frequency increases on Day 22 because the plasma level of one of these steroids, P, markedly declines, and 3) restoration of physiological plasma levels of both steroids in the absence of the ovary produces an unphysiological suppression of pulse frequency, i.e. results in a lower pulse frequency than normally occurs in the presence of these same plasma steroid levels in animals with their ovaries intact. One hypothesis consistent with the latter observation is that at the end of gestation in the rat the ovary may produce a factor which 'protects' the frequency of the LH pulse generator from the negative feedback action of ovarian steroids. This allows an increase in LH pulse frequency and mean blood LH levels, and thereby facilitates ovarian follicular development and the normal progress of the first postpartum estrous cycle.

Modulation of prolactin responses to gonadotropin releasing hormone by acute testosterone infusions in normal women

The administration of gonadotropin releasing hormone (GnRH) has been shown to stimulate prolactin (PRL), suggesting its role as an inducer of PRL release. This study addresses whether testosterone may modulate the release of PRL with GnRH during the early follicular phase when this stimulatory effect is not usually observed. Chromatographically pure testosterone was administered intravenously to 13 women in 2 doses (100 micrograms and 1000 micrograms) over a 6-hour period. GnRH (100 micrograms) was administered as a bolus 2 hours before and 4 hours after beginning testosterone. In addition, 3 women received testosterone twice, 3 months apart, with testolactone pretreatment on the second occasion. Serum testosterone rose in all patients and achieved maximum steady-state levels by 120 minutes. Serum estradiol (E2) was increased in subjects receiving the larger dose of testosterone but was unchanged with the lower dose and with the addition of testolactone. PRL did not increase significantly after GnRH before testosterone infusion but showed a significant increase after testosterone as well as after testosterone with testolactone. This effect did not appear to be dose-related.