Assessments of the functional capacity of the gonadotrophs in men: effects of estrogen and clomiphene

Effects of decreasing the frequency of gonadotropin-releasing hormone stimulation on gonadotropin secretion in gonadotropin-releasing hormone-deficient men and perifused rat pituitary cells

The effects of decreasing the frequency of pulsatile gonadotropin-releasing hormone (GnRH) stimulation on pituitary responsiveness were studied in (a) men with isolated GnRH deficiency who had achieved normal sex steroid levels during prior long-term pulsatile GnRH replacement and (b) perifused dispersed pituitary cells from male rats in the absence of sex steroids. In three groups of four GnRH-deficient men, the frequency of GnRH stimulation was decreased at weekly intervals from (a) every 2-3-4 h (group I), (b) every 2-8 h without testosterone replacement (group II), or (c) every 2-8 h with testosterone replacement (group III). In three groups of three columns of perifused dispersed pituitary cells, pulses of GnRH were administered every 2, 4, or 8 h. In groups I and II, mean area under the luteinizing hormone (LH) curve increased (P less than 0.025) and serum testosterone levels fell (P less than 0.035) as the frequency of GnRH stimulation was decreased. In group III, the area under the LH curve also increased (P less than 0.01) although serum testosterone levels were constant, thereby demonstrating that the increase in pituitary responsiveness to slow frequencies of GnRH stimulation occurs independently of changes in the sex steroid hormonal milieu. The area under the LH curve also increased in the perifused dispersed rat pituitary cells when the frequency of GnRH administration was decreased to every 8 h (P less than 0.05), thus demonstrating that the enhanced pituitary responsiveness to slow frequencies of GnRH stimulation is maintained even in the complete absence of gonadal steroids. Nadir LH levels fell in all three groups (P less than 0.01) as the frequency of GnRH stimulation was decreased. In contrast, mean peak LH levels, the rate of LH rise, and the rate of endogenous LH decay were constant as the frequency of GnRH stimulation was decreased. Finally, as the GnRH interpulse interval increased, mean LH levels fell, and mean follicle-stimulating hormone levels were stable or fell. These results indicate that (a) pituitary responsiveness to GnRH increases at slower frequencies of GnRH stimulation in models both in vivo and in vitro, (b) these changes in pituitary responsiveness occur independently of changes in gonadal steroid secretion, and (c) the increases in LH pulse amplitude and area under the curve at slow frequencies of GnRH stimulation are due to decreases in nadir, but not peak, LH levels. Slowing of the frequency of GnRH secretion may be an important independent variable in the control of pituitary gonadotropin secretion.

Actions of estradiol on discrete attributes of the luteinizing hormone pulse signal in man. Studies in postmenopausal women treated with pure estradiol

We assessed the time-dependent impact of estradiol on properties of the luteinizing hormone (LH) pulse signal in 12 hypoestrogenemic postmenopausal volunteers studied basally and after 1, 5, 10, and 30 d of estradiol delivery via an intravaginal Silastic ring. Computerized analysis of the plasma LH time series revealed a significant decrease in LH pulse frequency within 24 h of estrogen treatment, followed by a secondary increase (days 5 and 10), and then a sustained decline (day 30) in LH pulsatility. Estradiol also significantly suppressed incremental and maximal (but not fractional) LH pulse amplitudes in a biphasic manner. In contrast, LH peak duration was invariant until day 30 of estradiol replacement. These observations indicate that the well recognized biphasic actions of estradiol on mean serum LH concentrations can be modeled in relation to specific and time-dependent alterations in LH pulse frequency and amplitude.

The assessment of hypothalamic pituitary maturation during puberty with a combined clomiphene citrate/GnRH test in boys

The diagnosis of idiopathic delayed pubertal development in boys is difficult. A single GnRH test does not give information concerning hypothalamic maturity. After one week clomiphene citrate administration the LH reaction pattern is enhanced in subjects with maturing and depressed in subjects with immature hypothalamic-pituitary function.

Estrogens in the feedback regulation of gonadotropin secretion in men: effects of administration of estrogen to agonadal subjects and the antiestrogen tamoxifen and the aromatase inhibitor delta'-testolactone to eugonadal subjects

To elucidate the specific role of estrogens in the feedback regulation of gonadotropin secretion in men, basal and LRH-stimulated gonadotropin levels were studied in: Six agonadal subjects Six agonadal subjects continuously treated with 50 micrograms ethinylestradiol Six eugonadal subjects, treated with the aromatase inhibitor delta'-testolactone, which induced a reduction of estrogen levels, independently of testosterone. Further, to determine whether estrogens exert differential effects in time on LH and FSH secretion, the anti-estrogen tamoxifen was administered to: Six eugonadal subjects for two weeks and Six eugonadal subjects for six weeks. It was found that estrogens have a strong suppressive effect on both LH and FSH secretion. However, changes in estrogen levels and blocking of estrogen receptors are followed more rapidly by FSH than LH. Estrogens affect LRH-induced LH release more than basal LH levels; basal and LRH-stimulated FSH are approximately equally influenced. Basal and LRH-induced LH secretion are known to be more dependent upon previous LRH stimulation than FSH secretion. Since FSH followed changes of estrogens more rapidly than LH did, we postulate that the negative feedback action of estrogens on: LH secretion is predominantly exerted at the level of the hypothalamus, through inhibition of LRH secretion FSH secretion predominantly at the level of the pituitary through a direct action on the gonadotroph.

Pituitary gonadotropin responses to different modes and doses of intravenous luteinizing hormone-releasing hormone administration in normal men

In 22 potentially fertile men, pituitary gonadotropin secretion was investigated by intravenous luteinizing hormone-releasing hormone (LH-RH) administration. LH-RH was administered continuously (1 microgram/minute) and in a pulsatile fashion (20 micrograms at 20-minute intervals, 20 micrograms at 60-minute intervals, and 60 micrograms at 60-minute intervals), for 3 hours, under standardized conditions. Blood was collected continuously by means of an integrated sampling technique. The mean serum luteinizing hormone (LH) concentration after any type of pulsatile administration rose significantly more than after continuous LH-RH administration. The mean increase in LH after pulsatile LH-RH administration with a 60-micrograms dose and 60-minute intervals was significantly greater than after pulsatile administration with a 20-micrograms dose and 20- or 60-minute intervals. No differences were observed in follicle-stimulating hormone responses after any type of LH-RH administration. These data confirm the existence of a self-priming effect for LH in the men; and maximum pituitary stimulation, within the dosage range tested, is reached after pulsatile LH-RH stimulation with an interval of 60 minutes.

Estrogen positive feedback on LH secretion in transsexuality

In order to test the hypothesis whether there is variation in hormonal levels or response to hormonal manipulation that could permit a distinction between heterosexuals and transsexuals, we designed the following protocol: Six male-to-female (m-to-f) transsexuals, six heterosexual control females and six female-to-male (f-to-m) transsexuals were given estradiol benzoate (E2B) (4.5 micrograms/kg/12 hr) for five days. In the female population, E2B treatment was initiated on day 5 of the menstrual cycle. In all the subjects blood luteinizing hormone (LH) and follicle stimulating hormone (FSH), estradiol-17 beta (E2) and testosterone (T) levels were measured twice daily. Additionally, LH and FSH responses to LHRH (100 micrograms iv) stimulation prior to and on day 5 of the E2B treatment were evaluated. In the m-to-f transsexuals, T levels decreased sharply and progressively during estrogen treatment, along with a fall in LH and FSH levels. The magnitude of the LH and FSH responses to LHRH stimulation also decreased following estrogen administration. In the heterosexual female controls and in the f-to-m transsexuals, estrogen administration increased LH levels to a minimum of 100% above initial values from day 3 onwards. Interestingly, the magnitude of the LH increase in the f-to-m transsexuals was greater than that of the heterosexual female controls. In both groups, LHRH stimulation resulted in a greater LH response compared to that prior to estrogen treatment. Our present observations, based on blood hormonal levels and responses to hormonal manipulations do not permit a distinction between heterosexual females and f-to-m transsexuals. There was no convincing evidence for the existence of a positive estrogen feedback on LH secretion in m-to-f transsexuals. These results contradict some of the reported hypotheses concerning hormonal alterations in these individuals.

The effect of pulsatile and continuous intravenous luteinizing hormone-releasing hormone administration on pituitary luteinizing hormone and follicle-stimulating hormone release in normal men

In 14 healthy, potentially fertile men, pituitary gonadotropin responses were studied under standardized conditions. Luteinizing hormone-releasing hormone (LH-RH) was given as a continuous infusion of 1 microgram/minute for 4 hours or in a pulsatile fashion with 20 micrograms as an intravenous bolus at intervals of 20 minutes for 4 hours. Blood was collected continuously by means of an integrated sampling technique. The mean serum luteinizing hormone (LH) concentration showed an oscillating pattern around a plateau level reached within 45 minutes during continuous LH-RH administration. During pulsatile infusion, an identical pattern for the first 45 minutes was observed with, thereafter, a continuous increase from 105 minutes until the end of the infusion. The mean increase in the serum LH level during pulsatile administration was significantly higher (P = 0.00001) than the mean increase seen during continuous infusion. The follicle-stimulating hormone concentration revealed a gradual progressive increase after both methods of stimulation, without a significant difference in the mean increase between the two types of administration. This study demonstrates the existence of a self-priming effect of LH after pulsatile LH-RH administration in the man like that in the woman.

Biphasic effect of estradiol on luteinizing hormone response to gonadotropin-releasing hormone in castrated men

This study was designed to investigate the possibility that in men estradiol (E2) has a stimulatory effect on the gonadotropin response to GnRH. Nine castrated adult men, who presented extremely low testosterone (T) concentrations, received 5 mg/day estradiol benzoate (E2B) i.m. every 24 hr for several days, starting 5 days after orchidectomy. During E2B treatment the pituitary responsiveness to GnRH (100 micrograms given as an iv bolus) was tested after 24, 48, 72, 96, 120, and 144 hrs of E2B administration. The pituitary responsiveness to GnRH was also tested in untreated men from day 5 to day 10 following bilateral orchidectomy. In the E2B-treated subjects the increased serum estradiol concentrations induced an initial decrease and a subsequent increase of the LH response to GnRH. The responses were decreased after 24 hr of treatment; thereafter, the LH responses were progressively increased and were markedly augmented after 120 hr of E2B treatment. On the contrary, during treatment the FSH response to GnRH was preferentially blunted. In the untreated castrated men the LH and FSH responses to GnRH increased progressively from day 5 to day 10 after orchidectomy, but decreased responses were never observed during this period of observation. The maximum LH concentrations, which occurred at 30-60 min following GnRH in untreated castrated men, did not occur until 120-150 min in the E2B treated men.

Inter-relationship between changing patterns of LHRH and gonadotrophins in the menstrual cycle

Optimum conditions for a sensitive and highly precise radioimmunoassay of LHRH were established. Precipitation and removal of interfering substances and concentration of the resultant LHRH extracts from peripheral plasma were also achieved. Using these methods, daily plasma LHRH levels in females with normal menstrual cycles were measured and correlated with the corresponding LH and FSH levels. The levels of LHRH in the peripheral plasma of postmenopausal females, as well as eugonadal males, were also determined. The LHRH profile in normal cycling women was found to be cyclic but the peak LHRH levels were observed at the beginning of the rise in LH and FSH levels and preceded the midcycle surge of gonadotrophins. The LHRH levels in the luteal phase (19.8 +/- 1.1 pg/ml, mean +/- SEM) were significantly (P less than 0.01) higher than those in the follicular phase (16.5 +/- 0.5 pg/ml) of the menstrual cycle. A high degree of correlation (r = 0.91) was seen between the immunoreactivity and biological activity of the extracted LHRH.

Sex and alcohol: the effects of alcohol on the hypothalamic-pituitary-gonadal axis

Effects of alcohol on the hypothalamic-pituitary-gonadal axis are complex. Those at the gonadal level are best defined in studies such as those presented in this issue. However, there is an accumulating body of data supporting central effects of alcohol. The precise locus or loci is not certain. Further investigations probably including in vitro methodologies are likely to enhance our knowledge in this area. Our understanding of the effects of alcohol in the human female is especially limited.

The effect of clomiphene on uncastrated and castrated male transsexuals

Clomiphene was administered at a daily dose of 100 mg for 5 consecutive days to two groups of male subjects. There were three uncastrated male transsexuals (Group A) and nine castrated male transsexuals (Group B). In the uncastrated subjects Clomiphene enhanced the secretion of follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone (T) starting from day 3 of treatment. The magnitude of the increment ranged from 150%--250% over the mean basal plasma level for LH, 113%--262% for FSH and 12%--68% for T. In contrast, Clomiphene suppressed both FSH and LH in the castrated subjects. Equal suppression of both the gonadotrophins were observed. The levels of FSH and LH in plasma on day 3 were suppressed to 66.4% and 66.2% of their respective mean basal levels. Two days after the termination of treatment, suppressions were maintained. These results suggest that Clomiphene acts as an anti-oestrogen in uncastrated male transsexuals and in castrated male transsexuals who have subphysiological levels of oestradiol it acts as a weak oestrogen.

Effect of clomiphene citrate on plasma levels of immunoreactive luteinizing hormone-releasing hormone, gonadotropin, and testosterone in normal subjects and in patients with idiopathic oligospermia

The effect of clomiphene citrate on plasma immunoreactive luteinizing hormone-releasing hormone (LH-RH), gonadotropin, and testosterone levels was investigated in 10 patients with idiopathic oligospermia and in 10 normal volunteers. A daily 100-mg dose of clomiphene citrate induced a marked, significant increase in plasma immunoreactive LH-RH levels, followed by significant increments in gonadotropin and testosterone values. No significant differences were detected in LH-RH, gonadotropin, and testosterone levels between controls and patients with oligospermia either under basal conditions or during clomiphene treatment.

Reduced 'gonadotrophin response to releasing hormone' after chronic administration to impotent men

Ten endocrinologically normal men with secondary sexual impotence were given 500 microng LHRH subcutaneously every 8 h. After 4 weeks treatment the LH response to 500 microng LHRH was reduced from a peak of 35.7+/-5.2 to 16.8+/-3.5 mu/ml (P less than 0.01) and the FSH response from 4.2+/-0.93 to 2.39+/-0.4 mu/ml (P greater than 0.01). Circulating total testosterone, oestradiol, prolactin and sex hormone binding globulin showed no significant changes. Whether this inability of the pituitary to maintain it s response to LHRH is peculiar to impotent men requires further study.

The apparent paradox of the negative and positive feedback control system on gonadotropin secretion

The separate and interactive effects of estradiol (E2) and luteinizing hormone-releasing factor (LRF) on the dynamics of LH storage and release were studied. Measurements were made of the serum gonadotropin responses to submaximal doses of LRF, given as brief pulses or infused over an extended period to normal women at various stages of the follicular phase of their menstrual cycles and to hypogonadal women with and without estrogen treatment. The two-pool concept of pituitary gonadotropin was verified; the dynamic responses of the two pools to the inputs of LRF and E2 were investigated and related to pituitary properties of sensitivity and reserve. Our results indicate that LRF appears to serve as a primary drive on the gonadotrophs, stimulating gonadotropin synthesis and storage (second pool), as well as release (first). E2 for the most part, amplifies the action of LRF except that it impedes LRF-induced release of gonadotropin. E2 augments the second pool activity (reserve) preferentially, and the relative activity of the first pool appears to be influenced by the E2-dependent self-priming effect of LRF. The interactions of the various elements of the system, when combined, provide a U-shaped curve to describe the over-all capacity of the gonadotrophs as a function of a broad range of E2 inputs. Negative and possitive feedback of E2 are revealed to operate by different mechanisms and to represent different segments of a single U-shaped curve rather than paradoxically disparate actions.