Evidence that testosterone can suppress pituitary gonadotropin secretion independently of peripheral aromatization

SHBG and total testosterone levels in men with adult onset hypogonadism: what are we overlooking?

Background

Adult onset male hypogonadism (AOH) is a common clinical condition whose diagnosis and management are controversial, and is often characterized by a low level of SHBG, but our understanding of why testosterone levels are low when SHBG is low is incomplete.

Methods

This retrospective chart review was performed to compare the relationship between SHBG and testosterone in the plasma of men presenting for evaluation of AOH with a cohort of men treated chronically with transdermal testosterone.

Results

The level of SHBG was < 30 nmol/L in 73% of men who presented for evaluation of AOH, and was inversely proportional to BMI in both the untreated and the testosterone-treated men. As in previous populations, the level of SHBG was highly positively correlated (r = 0.71, p < 0.01) with the total testosterone level in untreated men presenting for evaluation of AOH, but no relationship was found between the level of SHBG and total testosterone among men who were being treated with a transdermal testosterone preparation.

Conclusions

These findings further support the idea that SHBG regulates testicular negative feedback either directly or by modulating the entry of testosterone or estradiol into cells in the hypothalamus and/or pituitary to control gonadotropin synthesis and secretion which explains in part the low testosterone levels in men with AOH.

Trial registration

Not applicable.

Androgens During Infancy, Childhood, and Adolescence: Physiology and Use in Clinical Practice

We provide an in-depth review of the role of androgens in male maturation and development, from the fetal stage through adolescence into emerging adulthood, and discuss the treatment of disorders of androgen production throughout these time periods. Testosterone, the primary androgen produced by males, has both anabolic and androgenic effects. Androgen exposure induces virilization and anabolic body composition changes during fetal development, influences growth and virilization during infancy, and stimulates development of secondary sexual characteristics, growth acceleration, bone mass accrual, and alterations of body composition during puberty. Disorders of androgen production may be subdivided into hypo- or hypergonadotropic hypogonadism. Hypogonadotropic hypogonadism may be either congenital or acquired (resulting from cranial radiation, trauma, or less common causes). Hypergonadotropic hypogonadism occurs in males with Klinefelter syndrome and may occur in response to pelvic radiation, certain chemotherapeutic agents, and less common causes. These disorders all require testosterone replacement therapy during pubertal maturation and many require lifelong replacement. Androgen (or gonadotropin) therapy is clearly beneficial in those with persistent hypogonadism and self-limited delayed puberty and is now widely used in transgender male adolescents. With more widespread use and newer formulations approved for adults, data from long-term randomized placebo-controlled trials are needed to enable pediatricians to identify the optimal age of initiation, route of administration, and dosing frequency to address the unique needs of their patients.

Gonadotrope androgen receptor mediates pituitary responsiveness to hormones and androgen-induced subfertility

Many women with hyperandrogenemia suffer from irregular menses and infertility. However, it is unknown whether androgens directly affect reproduction. Since animal models of hyperandrogenemia-induced infertility are associated with obesity, which may impact reproductive function, we have created a lean mouse model of elevated androgen using implantation of low dose dihydrotestosterone (DHT) pellets to separate the effects of elevated androgen from obesity. The hypothalamic-pituitary-gonadal axis controls reproduction. While we have demonstrated that androgen impairs ovarian function, androgen could also disrupt neuroendocrine function at the level of brain and/or pituitary to cause infertility. To understand how elevated androgens might act on pituitary gonadotropes to influence reproductive function, female mice with disruption of the androgen receptor (Ar) gene specifically in pituitary gonadotropes (PitARKO) were produced. DHT treated control mice with intact pituitary Ar (Con-DHT) exhibit disrupted estrous cyclicity and fertility with reduced pituitary responsiveness to GnRH at the level of both calcium signaling and LH secretion. These effects were ameliorated in DHT treated PitARKO mice. Calcium signaling controls GnRH regulation of LH vesicle exotocysis. Our data implicated upregulation of GEM (a voltage-dependent calcium channel inhibitor) in the pituitary as a potential mechanism for androgen's pathological effects. These results demonstrate that gonadotrope AR, as an extra-ovarian regulator, plays an important role in reproductive pathophysiology.

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 effects of diet on circulating sex hormone levels in men

There is considerable epidemiological evidence that a Western-style diet may increase the risk of certain hormone-dependent conditions in men via its effects on hormone metabolism. Experimental evidence also suggests that dietary factors may exert subtle effects on hormone metabolism. Here we review the clinical and epidemiological evidence that diet is associated with circulating sex hormone levels in men. In comparison with factors such as age and BMI, nutrients do not appear to be strong determinants of sex hormone levels. Dietary intervention studies have not shown that a change in dietary fat and/or dietary fibre intake is associated with changes in circulating sex hormone concentrations over the short term. The data on the effects of dietary phyto-oestrogens on sex hormone levels in men are too limited for conclusions to be drawn. Observational studies between men from different dietary groups have shown that a vegan diet is associated with small but significant increases in sex-hormone-binding globulin and testosterone concentrations in comparison with meat-eaters. However, these studies have not demonstrated that variations in dietary composition have any long-term important effects on circulating bioavailable sex hormone levels in men. This lack of effect may be partly explained by the body's negative feedback mechanism, which balances out small changes in androgen metabolism in order to maintain a constant level of circulating bioavailable androgens. It appears, therefore, that future studies should look for dietary effects on the feedback mechanism itself, or on the metabolism of androgens within the target tissues.

The effect of circulating estradiol concentrations on gonadotropin secretion in young and old castrated male-to-female transsexuals

CONTEXT

In aging men, circulating testosterone (T) declines which is associated with an increase in the levels of luteinizing hormone (LH) and follicle stimulating hormone (FSH) , albeit insufficient to maintain T at its original level. It has been speculated that a higher sensitivity of the hypothalamus and/or pituitary for the feedback effect of circulating sex hormones in older men is responsible.

OBJECTIVE

To compare the effect of experimentally varied plasma levels of estradiol on the LH and FSH secretion in young and old castrated male-to-female transsexuals, in almost absence of T. DESIGN, SUBJECTS, AND INTERVENTIONS: In 10 healthy, young (mean age 37.6 ± 6.2 years) and 11 healthy, old (mean age 68.1 ± 7.0) male-to-female transsexuals after gonadectomy plasma estradiol levels were experimentally varied with estradiol patches (the first week 100 μg/day patches, the second week 50 μg/day, the third week 25 μg/day and the fourth week no patch was applied) and plasma levels of LH and FSH were monitored after every week.

RESULTS

Mean plasma bioavailable estradiol (E2) levels in the two groups ranged between 13.6 and 104 pmol/l. LH and FSH were inversely related to peripheral estradiol levels, were lower in the old group at all time points reaching statistical significance in the last week of the study when no patch was applied and estradiol levels were extremely low.

CONCLUSIONS

The results of this study do not support the hypothesis of an age related increasing sensitivity of the hypothalamo-pituitary compartment for the negative feedback of E2, but suggest a deficient feed-forward drive in older male-to-female transsexuals.

Age disrupts androgen receptor-modulated negative feedback in the gonadal axis in healthy men

Testosterone (T) exerts negative feedback on the hypothalamo-pituitary (GnRH-LH) unit, but the relative roles of the CNS and pituitary are not established. We postulated that relatively greater LH responses to flutamide (brain-permeant antiandrogen) than bicalutamide (brain-impermeant antiandrogen) should reflect greater feedback via CNS than pituitary/peripheral androgen receptor-dependent pathways. To this end, 24 healthy men ages 20-73 yr, BMI 21-32 kg/m2, participated in a prospective, placebo-controlled, randomized, double-blind crossover study of the effects of antiandrogen control of pulsatile, basal, and entropic (pattern regularity) measurements of LH secretion. Analysis of covariance revealed that flutamide but not bicalutamide 1) increased pulsatile LH secretion (P = 0.003), 2) potentiated the age-related abbreviation of LH secretory bursts (P = 0.025), 3) suppressed incremental GnRH-induced LH release (P = 0.015), and 4) decreased the regularity of GnRH-stimulated LH release (P = 0.012). Furthermore, the effect of flutamide exceeded that of bicalutamide in 1) raising mean LH (P = 0.002) and T (P = 0.017) concentrations, 2) accelerating LH pulse frequency (P = 0.013), 3) amplifying total (basal plus pulsatile) LH (P = 0.002) and T (P < 0.001) secretion, 4) shortening LH secretory bursts (P = 0.032), and 5) reducing LH secretory regularity (P < 0.001). Both flutamide and bicalutamide elevated basal (nonpulsatile) LH secretion (P < 0.001). These data suggest the hypothesis that topographically selective androgen receptor pathways mediate brain-predominant and pituitary-dependent feedback mechanisms in healthy men.

Testosterone's short-term positive effect on luteinizing-hormone secretory-burst mass and its negative effect on secretory-burst frequency are attenuated in middle-aged men

BACKGROUND

Testosterone (T) production declines and LH pulses become smaller and more frequent in middle-aged men. The mechanisms underlying these changes are not known.

RATIONALE

Small frequent LH pulses in middle-aged men could reflect impaired feedback by systemic T.

HYPOTHESIS

Middle age disrupts negative feedback by T on selected facets of LH secretion.

SUBJECTS AND SETTING

Healthy men were studied at an academic medical center.

METHODS

The protocol comprised blockade of gonadal steroidogenesis and graded transdermal addback of T doses of 0, 2.5, 5, or 7.5 mg/d designed to span the castrate to physiological range of T concentrations in each of 23 healthy men ages 19-71 yr (interquartile range, 28-53 yr). We quantified 12-h basal and pulsatile LH secretion (92 time series) using a mathematically justified deconvolution method.

RESULTS

Stepwise T supplementation from the hypogonadal through the eugonadal range repressed mean (12-h) LH concentrations (P = 0.001). By regression analysis, age attenuated the capabilities of increasing T concentrations to 1) increase LH secretory-burst mass (P < 0.0001); and 2) decrease LH secretory-burst frequency (P = 0.025). Age did not alter T's feedback on basal LH secretion, interpulse regularity, the waveform of LH secretory bursts, or the slow half-life of LH.

CONCLUSION

Middle age impairs both the positive and negative actions of systemic T on pulsatile LH secretion in healthy men, thus potentially explaining earlier inconsistencies in feedback studies based upon single-sample mean LH concentrations. Longitudinal studies will be required to elucidate the precise age dependence of inferred dual feedback failure.

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.

Short-term aromatase-enzyme blockade unmasks impaired feedback adaptations in luteinizing hormone and testosterone secretion in older men

The mechanisms subserving hypoandrogenemia and relative hypogonadotropism in older men are not known. The present study tests the clinical hypothesis that aging impairs hypothalamopituitary adaptations to feedback withdrawal induced by antagonism of estrogen biosynthesis. To this end, we appraised gonadal axis responses to estrogen depletion induced by anastrozole (a potent and selective aromatase inhibitor) in nine older and 11 young men vs. placebo in 17 other older and eight young men. The study design comprised a prospectively randomized, double-blind, parallel-cohort intervention. To monitor LH release, blood was sampled every 10 min for 24 h; LH concentrations were assayed by two-site monoclonal immunoradiometric assay; pulsatile LH release quantitated by a model-free discrete peak-detection technique (Cluster); feedback-dependent orderliness of LH secretion via the approximate entropy statistic; and 24-h rhythmicity of LH concentrations by cosine analysis. At baseline, older men had comparable estradiol and testosterone but lower LH concentrations than young controls. Exposure to anastrozole reduced (24-h pooled) serum estradiol concentrations by 50% (P < 0.001) and elevated mean LH concentrations by 2.1-fold (P < 0.001) in both the young and older cohorts. However, older men failed to achieve young adult augmentation of the following: 1) total testosterone concentrations (P < 0.01) or molar testosterone to SHBG ratios (P < 0.01); 2) incremental LH pulse amplitude (P < 0.001) and LH peak area (P < 0.01); 3) mean LH pulse frequency (P = 0.0044); and 4) quantifiable irregularity (approximate entropy) of LH release patterns (P < 0.001). FSH concentrations became comparable in the two age cohorts. In summary, administration of a potent and selective aromatase antagonist reduces estradiol and elevates mean LH concentrations equivalently in young and older men. The low estrogen-feedback state in elderly men unmasks diminished incremental LH pulse amplitude and area; absence of further acceleration of LH pulse frequency; impaired regulation of the orderliness of LH release; and reduced testosterone to SHBG ratios. Thus, aging alters expected hypothalamopituitary-gonadal adaptations to short-term partial estrogen depletion in healthy men.

Metformin versus flutamide in the treatment of metabolic consequences of non-obese young women with polycystic ovary syndrome: a randomized prospective study

In addition to the reproductive consequences, polycystic ovary syndrome (PCOS) is characterized by a metabolic disorder in which hyperinsulinemia and insulin resistance are central features. The effects and possible benefits from insulin-sensitizing drugs are not well known, especially in non-obese women with PCOS. This study was designed to evaluate the effects of metformin and flutamide on metabolic parameters and insulin resistance in non-obese women with PCOS. Thirty non-obese women newly diagnosed with PCOS and 15 age- and weight-matched healthy volunteers as controls were included in the study. Patients were assigned randomly to receive flutamide 250 mg daily or metformin 850 mg three times daily. Glucose, insulin, insulin resistance, androgen levels and glucose and insulin responses to an oral glucose tolerance tests (OGTT) were assessed before and after a 4-week therapy period. A positive correlation was found between body mass index and insulin level in patients with PCOS and controls. Follicle stimulating hormone, luteinizing hormone, free testosterone and dehydroepiandrosterone sulfate levels decreased significantly, but insulin resistance levels were not changed after flutamide therapy. Body weight, free testosterone, insulin and insulin resistance levels decreased significantly after metformin therapy. In conclusion, metformin treatment improved insulin sensitivity and decreased androgen levels, and flutamide decreased androgen levels but failed to improve insulin sensitivity in the non-obese women with PCOS.

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.

Regulation of lutenizing hormone secretion and subunit messenger ribonucleic acid expression by gonadal steroids in perifused pituitary cells from male monkeys and rats

The mechanisms by which gonadal steroids regulate gonadotropin secretion remain incompletely understood. As previous studies suggest that the pituitary actions of testosterone (T) and estradiol (E) differ in male primates and rodents, we compared the effects of 10 nM T, 0.1 nM E, and 10 nM dihydrotestosterone (DHT) on the LH response to hourly pulses of GnRH as well as the GnRH receptor (GnRH-R) and LH subunit messenger RNA (mRNA) levels in dispersed pituitary cells from intact male monkeys and rats. T suppressed (P < 0.01) and E increased (P < 0.05) GnRH-stimulated LH secretion by rat pituitary cells. With monkey pituitary cells, on the other hand, there was no significant effect of either T or DHT on GnRH-stimulated LH secretion. In E-treated monkey cells, a period of initial enhancement (P < 0.05) was followed by significant suppression (P < 0.05) of LH secretion. GnRH-R mRNA was unchanged by T or E in either rat or monkey cells. T suppressed LHbeta (P < 0.01) and alpha-subunit (P < 0.01) mRNAs, whereas E increased alpha-subunit (P < 0.01), but did not alter LHbeta mRNA levels in rat cells. In monkey cells, however, neither T nor E affected LHbeta or alpha-subunit mRNA levels significantly. Our results identify different regulatory mechanisms by which testicular steroid hormones control LH secretion by the pituitary in male primates and rodents. We propose that the primary site of androgen negative feedback in the male primate is to restrain GnRH pulsatile secretion, whereas in the male rat T also decreases gonadotropin synthesis and secretion by directly affecting the pituitary. E suppresses GnRH-stimulated LH secretion in the primate pituitary, but amplifies the action of GnRH in the rat. Our data also reveal that the action of T to suppress LH secretion and subunit mRNA in male rats is not through decreased GnRH-R gene expression.

Luteinizing hormone secreting adrenal tumour as a cause of precocious puberty

A boy aged 6 years presented with genital precocity, enlarged testes and advanced linear growth. An ovoid mass 3-4 cm in diameter was identified by MRI scan in the right adrenal gland. Serum concentrations of LH, testosterone, alpha-subnuit, dehydroepiandrosterone sulphate, androstenedione and oestradiol were persistently elevated. LH was unresponsive to bolus i.v. injection of GnRH or to GnRH analogue therapy. Serum FSH was normal. After removal of the adrenal tumour, serum LH, alpha-subunit, testosterone and adrenal androgen levels fell to normal. In incubation medium of cultured disaggregated tumour cells, LH concentrations were greater than twice the mean serum concentration and 4-5-fold higher than in the medium of cultured non-neoplastic adrenal cells. Specific immunostaining of the tumour was positive for LH and alpha-subunit in many areas and these were not found in the adjacent non-neoplastic adrenal. Testicular biopsy showed almost complete spermatogenesis although germinal cell types were numerically lower than in normal men. These findings are consistent with an adrenocortical adenoma secreting LH being the cause of the patient's precocious puberty.

Clinical features and hormonal characteristics in a case of ovarian arrhenoblastoma

We report a case of a 34-year-old woman affected with ovarian arrhenoblastoma characterized by very high testosterone (T) levels (34.0-60.0 ng/ml; n.v.0.2-0.9) and suppressed gonadotropin levels. The physical examination revealed: severe hirsutism, acne, amenorrhea and other virilization signs. Basal hormonal evaluation also showed a markedly elevated 17-hydroxyprogesterone (17-OHP) and a mild delta 4 Androstenedione (A) and dehydroepiandrosterone sulfate (DHEAs) increase. ACTH test induced only slight changes in androgen secretion. By contrast, dexamethasone test greatly decreased A and DHEAs whereas T levels were only partially suppressed. Moreover, hCG test was clearly stimulatory for T and A. Suppressed gonadotropin levels did not respond to LHRH stimulation. The removal of the neoplasia was followed by normalization of T levels and increase of serum gonadotropins with subsequent restoration of a normal responsiveness to LHRH and resumption of an ovulatory menstrual cycle. This observation suggests that the high T levels played a primary role in the pathogenesis of the gonadotropin suppression and anovulation. Recovery of acne was complete whereas hirsutism score was reduced but still elevated after one year. This may be due to postoperative A and DHEAs levels slightly above the normal range, indicating the presence of adrenal hyperandrogenism.

Quantification of androgen receptor and follicle-stimulating hormone receptor mRNA levels in human and monkey testes by a ribonuclease-protection assay

A sensitive, solution-hybridization ribonuclease-protection assay (RPA) was established to quantify the expression of mRNA for the androgen receptor (AR) and follicle-stimulating hormone receptor (FSHR) in total RNA samples isolated from tissues of the cynomolgous monkey, human testes obtained from elderly patients undergoing orchidectomy because of prostatic carcinoma or from transsexual men undergoing gender reassignment as well as human cell lines DU 145, REP and RVP. Sensitivity experiments revealed that, in the human and monkey, 1-2 micrograms of total RNA were sufficient to achieve quantifiable signals of the different receptor mRNA species. Quantification of AR and FSHR mRNA levels showed a 1.7-fold higher expression of AR mRNA and a 2.4-fold higher expression of FSHR mRNA in the monkey testes compared to human testes from patients with prostatic carcinoma. Normal spermatogenesis in both human and monkey testes indicated no relationship between spermatogenic status and receptor expression. The significantly lower expression of AR and FSHR mRNA in humans than in monkeys might therefore be either age- or species-related. Quantification of mRNA for AR and FSHR in the testis of the transsexual patients undergoing oestrogen and antiandrogen treatment displayed a drastic increase (4.5-fold) in mRNA for the AR, whereas mRNA for the FSHR was barely detectable. Due to its high sensitivity, reproducibility and its ability to quantify mRNA transcripts, the RPA is a useful tool for investigating expression of low abundant receptor genes and their regulation when only very small amounts of tissue are available. Furthermore, it is suitable for use in clinical and experimental studies in which accurate quantification of transcripts is necessary.

The reproductive system of male rats exposed to very low doses of ionizing radiation, 1: Hormonal profile of animals exposed after sexual maturity

Adult male rats were treated with a single, whole body exposure to a dose of 0.001, 0.01 or 0.1 Gy (1 Gy = 100 rad). The animals were sacrificed 1, 7, 30, 100 or 180 days following exposure. Serum testosterone, serum and hypophyseal LH, FSH and prolactin as well as hypothalamic LHRH were measured. In the 0.1 Gy irradiated rats, serum LH and FSH were 100% higher and serum prolactin was 30% lower as compared to controls, 30 days after irradiation. The concentrations of these hormones remained significantly different from control values even after 180 days after exposure. On the other hand, the hypophyseal content of LH, FSH and prolactin decreased in the 0.1 Gy treated rats, 100 days after irradiation. In the group of the 0.01 Gy irradiated rats, serum FSH increased by 70% and hypophyseal FSH decreased. No changes were observed in serum testosterone and hypothalamic LHRH in any of the irradiated groups and no changes were observed in the group exposed to 0.001 Gy. It may be concluded that a long term damage to the reproductive system of the male rat was induced by a single, whole body exposure to 0.1 Gy of gamma radiation.

Treatment of men with idiopathic oligozoospermic infertility using the aromatase inhibitor, testolactone. Results of a double-blinded, randomized, placebo-controlled trial with crossover

The hypothesis that increased estradiol production may be the cause of impaired spermatogenesis in infertile men with idiopathic oligozoospermia was tested by administering the aromatase inhibitor, testolactone, and by assessing its effects on sperm output and fertility. Our study was a randomized, placebo-controlled double-blind crossover trial. Subjects (n = 25) with infertility due to unexplained oligozoospermia were given testolactone (2 g/day) or placebo for 8 months followed by crossover to the other treatment for an additional 8 months. Total estradiol and testosterone levels during testolactone exposure did not change from basal and placebo values. However, sex hormone-binding globulin binding capacity consistently decreased (30%, p less than 0.01) and free testosterone levels increased (36%, p less than 0.01). Free estradiol values increased but not significantly. Additionally, LH and FSH serum levels increased by 15% and 20%, respectively (p less than 0.05), and 17 alpha-hydroxyprogesterone values increased by 90% (p less than 0.05) during drug administration. Sperm output and semen quality remained unchanged during either testolactone or placebo treatment, and no pregnancies occurred during the 16-month study. These data suggest that chronic administration of testolactone at this dose fails to maintain aromatase inhibition despite depression of 17,20-desmolase activity with elevated 17 alpha-hydroxyprogesterone and depressed SHBG binding capacity with elevation of free testosterone. Testolactone is not efficacious in the treatment of idiopathic oligozoospermic infertility.

Ovulation induction with pulsatile luteinizing hormone-releasing hormone in women with clomiphene citrate-resistant polycystic ovary-like disease: endocrine results

The pituitary and gonadal response to pulsatile luteinizing hormone-releasing hormone (LH-RH) administration during the first and consecutive second treatment unit (TU) was studied in nine women with clomiphene citrate-resistant polycystic ovary-like disease (PCOD). The control group consisted of eight eumenorrheic women. Luteinizing hormone levels, LH amplitudes, and total urinary excretion/24 hours did not differ between ovulatory and anovulatory TUs, but were significantly higher compared with the control group. Follicle-stimulating hormone (FSH) in PCOD did not differ from normal cycles. Androgen values in the anovulatory TUs were significantly higher compared with the ovulatory TUs (P = 0.001). We conclude that LH-RH therapy may result in ovulation; however, it does not redress the intrinsic abnormality in PCOD and FSH, and androgen levels do not seem to be critical in ovulation induction.

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

Intravenous testosterone was infused for 6 hours in 23 ovulatory women, divided into five groups according to dose, to assess the effects of testosterone on gonadotropin secretion. Serum testosterone increased from 0.24 +/- 0.08 to steady-state levels of 1.63 +/- 0.18 ng/ml in the lowest-dose group (1) and to 42.1 +/- 3.3 ng/ml in the highest-dose group (4). In another group (5), patients were pretreated with testolactone, which prevented the estradiol rise associated with testosterone infusion. All groups except group 1 exhibited significant reductions in the delta maximum responses of luteinizing hormone to gonadotropin-releasing hormone during testosterone infusion compared with pretreatment levels (p less than 0.01). This was also evident for the testolactone group (5). There were no observed changes in serum follicle-stimulating hormone. Luteinizing hormone pulse frequency was decreased (p less than 0.05) with testosterone concentrations of 27.2 +/- 0.77 and 42.1 +/- 3.3 ng/ml (groups 3 and 4), but only in the highest group (4) was there a decrease in pulse amplitude (p less than 0.05). No luteinizing hormone pulse changes were observed with lower concentrations of testosterone. Plasma immunoreactive gonadotropin-releasing hormone levels remained undetectable or low in some of the groups sampled. These data suggest that short-term infusions of testosterone inhibit hypothalamic-pituitary function of normal women when high doses are used, and this effect may be independent of aromatization to estrogen.

Regulation of gonadotropin secretion in the male: effect of an aromatization inhibitor in estradiol-implanted, orchidectomized dogs

Testosterone is aromatized to estradiol in both peripheral tissues and the central nervous system. Various authors have suggested that this conversion in the male may be prerequisite for the regulation of gonadotropin secretion by testosterone. Previously, it was reported that inhibition of central nervous system aromatase caused a significant increase in plasma LH in the presence of physiologic testosterone levels (Winter et al, 1983). In order to confirm whether aminoglutethimide, the aromatase inhibitor used in our previous study, either blocked aromatization, or the action of estradiol, the following study was conducted. Fifteen male mongrel dogs were equally divided into three groups. Group 1 dogs were implanted with estradiol-filled polydimethylsiloxane capsules only; Group 2 dogs were implanted with empty capsules and treated with 60 mg b.i.d. of aminoglutethimide; and Group 3 dogs were implanted with polydimethylsiloxane capsules filled with estradiol and treated with aminoglutethimide. Blood samples were drawn for 24 days during pretreatment, capsule implantation, castration, aminoglutethimide administration and capsule removal periods. The postcastration response of both plasma LH and FSH in dogs in groups 1 and 3 was suppressed in the presence of elevated estradiol, whereas that of Group 2 dogs was normal in the absence of estradiol. The results suggest that aminoglutethimide neither directly affects the plasma concentration of either LH or FSH nor blocks the effect of estradiol in inhibiting their release following castration. These data, taken together with our previous work, implicate aromatization of testosterone to estradiol in the control of gonadotropin secretion in the male.

Selective reduction of elevated FSH levels in infertile men by pulsatile LHRH treatment

In order to investigate whether isolated elevated FSH levels in men with idiopathic oligospermia can be lowered by pulsatile LHRH therapy, six patients were treated for 6 weeks with 5 micrograms LHRH pulses every 2 h. The pulses were delivered from a portable minipump (Zyklomat) through a subcutaneously inserted needle. At the end of treatment prepulse serum LH levels were no different from the levels before treatment while serum FSH was significantly reduced in all patients (16.9 +/- 2.5 U/l vs 11.3 +/- 1.9 U/l, mean +/- SEM; P less than 0.01). The normal FSH range was reached in one of the six patients. The areas under the LH curves following the first and the last (i.e. 504th) pulse were no different, while the areas under the FSH curves were significantly smaller (2870 +/- 434 vs 1776 +/- 237 U/l X min; P less than 0.01). Serum testosterone and oestradiol were significantly higher at the end of treatment (11.0 +/- 1.2 vs 15.2 +/- 1.9 nmol/l 146 +/- 18 vs 214 +/- 25 pmol, respectively). Thus increased FSH levels in men with idiopathic oligospermia can be selectively reduced by pulsatile LHRH treatment. If the increased FSH levels are not the result but rather a factor contributing to the pathogenesis of certain types of oligospermia these findings may have implications for the treatment of this condition.

Aromatase in breast cancer and the role of aminoglutethimide and other aromatase inhibitors

Approximately one third of human breast carcinomas are hormone dependent and regress upon reduction of circulating estrogen levels. Traditional treatment strategies utilized surgical ablative methods to lower estrogen concentrations as treatment of breast cancer. Currently, investigative emphasis is focused upon development of highly specific antiestrogens and inhibitors of estrogen production. The enzyme, aromatase, as the terminal step in estrogen biosynthesis, is a logical target for blockade with potent and specific inhibitors. The earliest available aromatase antagonist, aminoglutethimide, suppresses estrogen production to the same extent as surgical ablation and is an effective treatment for breast cancer. Aminoglutethimide, however, blocks other cytochrome P-450-mediated steroid hydroxylations, requires concomitant glucocorticoid administration, and is associated with initial side effects. Several more specific inhibitors by destroying aromatase irreversibly as well as by competitive inhibition. One of these, 4-hydroxy-androstenedione, has been intensively studied in animals and is undergoing clinical trial. New data regarding these inhibitors further emphasize the key role of aromatase in estrogen production and the practical utility of blocking this enzyme.

Effect of aromatase inhibition by delta 1-testolactone on basal and luteinizing hormone-releasing hormone-stimulated pituitary and gonadal hormonal function in oligospermic men

Aromatase inhibition by delta 1-testolactone (TL), 500 mg twice daily for 4 weeks, in nine patients with idiopathic oligospermia lowered circulating estradiol (E2) levels by about 30%, enhanced the secretion of follicle-stimulating hormone (+ 30%), 17-hydroxyprogesterone (17-OHP) (+ 40%), and testosterone (T) (+ 30%), but did not affect serum luteinizing hormone levels. Despite E2 lowering, there was an accumulation of 17-OHP over T, suggesting 17, 20-lyase inhibition. Unexpectedly, administration of TL almost completely deleted the T response to continuous luteinizing hormone-releasing hormone infusion present before TL therapy, despite similar gonadotropin release. Because the 17-OHP response to the luteinizing hormone-releasing hormone infusion was even higher during therapy, the 17,20-lyase lesion seemed aggravated despite substantial reduction of E2 levels. Although the present data suggest that estrogens play a less dominant role in the origin of the late steroidogenetic lesion than previously assumed, the suggestion also arises that TL per se, in addition to its antiestrogenic action, exerts an inhibiting effect on the 17,20-lyase locus, which may obscure the beneficial effect of reducing E2.

Short-term effects of testolactone on human testicular steroid production and on the response to human chorionic gonadotropin

Testicular responsiveness to a single dose of human chorionic gonadotropin was studied in five normal men before and during short-term treatment with an aromatization inhibitor, testolactone (TL). TL alone resulted in significant increases in the serum concentrations of progesterone, 17-hydroxyprogesterone, 17-hydroxypregnenolone, dehydroepiandrosterone, androstenedione, and the sulfate conjugates of pregnenolone, 17-hydroxypregnenolone and testosterone (T). Concentrations of 5-androstene-3 beta, 17 beta-diol and T remained unchanged, and those of estradiol (E2) decreased. TL had no major influence on serum luteinizing hormone, follicle-stimulating hormone, prolactin, or sex-hormone-binding globulin concentrations. During TL administration, human chorionic gonadotropin stimulation led to a significantly decreased E2 response, but the T response was unchanged. Alleviation of an inhibitory influence of E2 on the steroidogenic enzymes, especially 17,20-desmolase, was probably the reason behind the increased synthesis of several T precursors. In addition, TL appeared to have an inhibitory influence on the 17 beta-reduction of T precursors. TL resulted in increased serum concentrations of some steroid sulfates, but the mechanism of this effect remains unclear.

Alteration of hormone levels in normal males given the anabolic steroid stanozolol

Anabolic steroids have widespread metabolic effects but, to date, their proven clinical indications have been limited. Recently the 17 alpha-alkylated steroid, stanozolol, has been shown to be of value in a variety of commonly occurring vascular diseases. Its endocrine effects have received little attention and we have investigated the effect of administering a 14 d course of stanozolol (10 mg orally per day) on a variety of important hormonal pathways in nine healthy male subjects. Significant changes occurred as follows: a 55% reduction in serum testosterone levels was noted and was accompanied by reductions in 'derived' free testosterone, sex hormone binding globulin and LH levels; total T4 and T3 levels fell in association with a decrease in thyroxine binding globulin, but no alteration was detected in TSH or free T4 levels. Changes in vitamin D status, with falls in 25-hydroxycholecalciferol and vitamin D binding globulin were also observed. These effects were reversible on stopping treatment. Stanozolol therapy therefore leads to a number of hormonal changes, probably by an action at both pituitary and hepatic levels.

Androgens in the feedback regulation of gonadotropin secretion in men: effects of administration of dihydrotestosterone to eugonadal and agonadal subjects and of spironolactone to eugonadal subjects

To study the role of androgens in the feedback regulation of gonadotropin secretion, we measured the effects of administration of dihydrotestosterone undecanoate (DHTU) and of spironolactone. Basal and LRH stimulated LH/FSH levels were determined in: Six eugonadal men, before and after six weeks' DHTU 120 mg/day. Six agonadal subjects after 12 weeks' DHTU 120 mg/day. The results of B were compared to those of Six agonadal subjects without sex steroid treatment. Six eugonadal subjects were studied before and after six weeks' administration of spironolactone. In the two groups of eugonadal subjects, administration of either dihydrotestosterone or spironolactone had no effect on basal and LRH-stimulated gonadotropin levels. A clear but modest suppression was observed in agonadal subjects. Possibly DHT exerts some suppressive effect on gonadotropin secretion in the absence of other testicular products (estradiol, testosterone, inhibin), known to play a role in the negative feedback regulation. From these data it seems unlikely that in the eugonadal male circulating DHT has an important role in the feedback regulation of gonadotropin secretion.

The effect of delta 1-testolactone on serum testosterone and estradiol in the adult male rat

delta 1-Testolactone, an androgen derivative without intrinsic hormonal action, is known to block the aromatization of androgens to estrogens. This study was designed to assess its effect upon serum testosterone (T) and estradiol (E2) in the adult male rat. By itself, testolactone (TL) did not affect T/E2 levels in the dosages utilized. Daily injections of human chorionic gonadotropin (hCG) for 15 days caused a tenfold rise in serum T, although there was no increase in serum E2. When given along with hCG, TL did not alter the Leydig cell response. However, pretreatment of animals with TL increased the testicular response to hCG over that of saline-treated animals. Studies were also carried out to delineate the sources of estrogen in the adult male rat. These experiments demonstrate that (1) the majority of E2 is not testicular in origin but is derived from the adrenal; (2) the conversion of androgen precursors to E2 in the rat is not affected by TL; and (3) in spite of no demonstrable inhibition of E2 production, TL causes an increased Leydig cell responsiveness to hCG.

Quantitation of testolactone and 4,5-dihydrotestolactone in plasma and urine using high-performance liquid chromatography

A rapid, sensitive, and selective assay is described for the quantitation of both testolactone and its recently identified metabolite, 4,5-dihydrotestolactone, in plasma and urine using high-performance liquid chromatography. The procedure includes a methylene chloride extraction prior to chromatography and quantitation using peak height ratios (ultraviolet absorbance detection, 242 nm) of testolactone and 4,5-dihydrotestolactone to the internal standard, testosterone. A sensitivity of 20 ng/ml for both testolactone and 4,5-dihydrotestolactone is easily achieved using only 0.5 ml of sample. Mean recoveries for testolactone and its metabolite are 95.0% and 81.8%, respectively, and the mean coefficient of variation of the procedure is 3.5% for the drug and 7.1% for the metabolite. This method is currently being used to study the pharmacokinetics of testolactone and 4,5-dihydrotestolactone in male patients. A steady-state plasma concentration versus time profile from a representative patient is included.

Circannual rhythms of plasma luteinizing hormone, follicle-stimulating hormone, testosterone, prolactin and cortisol in prepuberty

For a period of four years we have been studying 106 healthy males and 66 healthy females, aged 6-10, by cross-sectional design, to look for evidence of a circannual rhythm in LH, FSH, testosterone, PRL, and cortisol secretion. Plasma samples were taken at 0800 h and all hormones were measured by RIA. A cosine function was fitted to the single data to indicate any significant circannual (about 1 year) rhythm and to estimate its parameters: mesor, amplitude, and acrophase. Annual changes were validated in the secretion of: LH (annual crest time in January in both sexes), testosterone (studied only in males, annual crest time in July), and PRL (significant rhythm only in females with annual crest time in March). FSH and cortisol did not show an annual rhythm in both sexes. Our data suggest that sex influences the circannual hormonal rhythms from prepuberty onwards.

Regulation of gonadotropin secretion in the male dog. Role of estradiol

Steroid regulation of pituitary LH and FSH secretion in the male may be mediated via the direct action of testosterone, or via the conversion of testosterone to either dihydrotestosterone (DHT) or estrogenic steroids. The site of testosterone conversion to these metabolites may be peripherally and/or centrally located. The purpose of this study was to investigate the importance of the conversion of testosterone to estradiol in the control of gonadotropin secretion using the aromatase inhibitor aminoglutethimide (AG). In testosterone-implanted orchidectomized dogs, AG prevented the ability of testosterone to inhibit the post-orchidectomy rise of LH, despite the presence of normal plasma concentrations of both testosterone and estradiol. These data suggest that aromatization of testosterone to estradiol is a necessary step in the regulation of LH secretion. Furthermore, a lack of change in the peripheral concentrations of estradiol in the presence of AG led us indirectly to conclude that inhibition of aromatization occurred centrally rather than peripherally. In the absence of AG, testosterone was unable to maintain intact levels of FSH in the orchidectomized dog for more than six days. Thus, it still remains to be demonstrated whether steroids are of major importance in the regulation of FSH secretion.

Hydrotestolactone lowers serum oestradiol and PRL levels in normal men: evidence of a role of oestradiol in prl secretion

The effect on serum PRL levels of lowering serum oestradiol (E2) concentration by short-term administration of an aromatase activity inhibitor, hydrotestolactone (HT), was studied in six healthy male subjects. After HT administration serum E2 levels decreased from 68 +/- 5.8 to 26 +/- 2.5 pmol/l (mean +/- SE, P less than 0.05). These E2 changes were accompanied by a significant decrease in mean 2-h PRL levels from 11.2 +/- 2.1 to 6.5 +/- 1.6 ng/ml mean +/- SE, P less than 0.05). The evaluation of individual percentage change from basal concentrations showed a varying decrease in all subjects. These findings suggest that under physiological conditions E2 may be one of the factors which control blood PRL concentrations in men.

Evidence that brain aromatization regulates LH secretion in the male dog

A variety of data suggest an independent role for androgens and estrogens in the regulation of luteinizing hormone (LH) secretion in the male. Estrogens, in the male are primarily derived from testicular androgens that are aromatized both in peripheral tissues and in the CNS. Our prior data suggested a pharmacologic regimen that blocked CNS aromatization without lowering peripheral estrogen or testosterone levels. Such experimental conditions would permit assessment of the relative roles of CNS versus peripheral aromatization in the regulation of LH secretion. We utilized this regimen (aminoglutethimide, a potent aromatase inhibitor, and hydrocortisone) in seven adult male dogs for 14 days. Plasma LH rose to castrate levels, 450% above control values on days 7 and 14. These LH increments stimulated similar rises in androstenedione, testosterone, and dihydrotestosterone. In contrast, plasma estrone and estradiol concentrations remained constant. The induction of castrate LH levels without a concomitant fall in peripheral androgens or estrogens is best explained by a block of central aromatization and thus a reduction in local hypothalamic concentrations. We conclude that aromatization in the CNS rather than peripheral tissues is the more important site with respect to LH negative feedback in the male dog.