Modifications of the gonadal function in the adult rat after fetal exposure to spironolactone

The effects of fetal exposure to spironolactone (SPL), an aldosterone antagonist with weak antiandrogen and gestagen properties, upon the pituitary-gonadal axis were studied in the offspring of rats that had been treated daily from gestation day 14 to day 20 with 10 or 20 mg SPL or the solvent vehicle (for controls). At 70-80 days of age, SPL-exposed rats showed no alterations in external genitalia or in body weight. However, males displayed a dose-dependent decrease in the weights of the ventral prostate and seminal vesicles. Whereas basal and gonadotropin-releasing hormone (GnRH)-induced plasma luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone, and 5 alpha-dihydrotestosterone levels were similar to controls, basal plasma and pituitary prolactin (Prl) levels were reduced (SPL-exposed 6.8 +/- 1.0 vs. controls 15.8 +/- 2.8 ng/ml and 6.1 +/- 1.2 vs. 11.6 +/- 1.8 microgram/anterior pituitary gland; mean +/- SEM). Cytosolic androgen receptors in ventral prostate were nonsignificantly decreased, but they increased after GnRH in contrast to controls. Nuclear androgen receptors were normal. Females displayed normal estrous cycles. Basal and GnRH-induced plasma FSH, Prl, estradiol, and progesterone concentrations were similar to controls, whereas plasma LH was elevated. Estrogen receptors in uterine cytosol were low and increased after GnRH. Ovaries and uteri were enlarged. The present study demonstrates that in utero exposure to SPL leads to endocrine dysfunctions that persist into adulthood. They are characterized in males by hypoprolactinemia, reduced weights of accessory sex organs, and a suggestion of functional modifications of androgen receptors. In females they are characterized by increased LH secretion, increased ovarian and uterine weights, and decreased uterine cytosol estrogen receptors, suggesting enhanced estrogenic action.     

Catecholamines and pituitary function. VI. Effect of different dopamine doses on TRH-induced prolactin release in women with pathological hyperprolactinemia

The present study was designed to examine the effect of low-dose dopamine (DA) infusion rates (0.02 and 0.1 microgram/kg X min) on both basal and TRH-stimulated prolactin release in normal and hyperprolactinemic individuals. Sixteen normally menstruating women in the early follicular phase of a cycle and 23 hyperprolactinemic patients were studied. 0.1 microgram/kg X min DA was infused in 8 normal women and 15 patients with pathological hyperprolactinemia, while 8 normal controls and 8 patients received 0.02 microgram/kg X min DA TRH (200 micrograms, i.v.) was administered alone and at the 180th min of the 5-hour DA infusion in all controls and patients. A significant reduction in serum PRL levels, which was similar in normal women (-59.5 +/- 4.0%, mean +/- SE) and hyperprolactinemic patients (-48.2 +/- 5.5) was observed in response to 0.1 microgram/kg X min DA. In normal cycling women DA infusion significantly (P less than 0.02) reduced the PRL response to TRH with respect to the basal TRH test (delta PRL 45.0 +/- 7.0 vs. 77.9 +/- 15.4 ng/ml). On the contrary, the PRL response to TRH was significantly higher during 0.1 microgram/kg X min DA than in basal conditions in hyperprolactinemic patients, both in absolute (delta PRL 91.8 +/- 17.6 vs. 38.4 +/- 6.8, P less than 0.03) and per cent (198.5 +/- 67.6 vs. 32.1 +/- 7.5, P less than 0.02) values. A normal PRL response to TRH, arbitrarily defined as an increase greater than 100% of baseline, was restored in 11 out of 15 previously unresponsive hyperprolactinemic patients.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of prolonged treatment with diltiazem on pituitary secretion of luteinizing hormone, follicle-stimulating hormone, thyrotropin and prolactin.

In previous studies it has been observed that acute administration or short-term treatment with calcium channel blockers can influence the secretion of some pituitary hormones. In this study, we have examined the effect of the long-term administration of diltiazem on luteinizing-hormone (LH), follicle-stimulating hormone (FSH), thyrotropin (TSH) and prolactin (PRL) levels under basal conditions and after gonadotropin-releasing hormone (GnRH)/thyrotropin-releasing-hormone (TRH) stimulation in 12 subjects affected by cardiovascular diseases who were treated with diltiazem (60 mg 3 times/day per os) for more than 6 months and in 12 healthy volunteers of the same age. The basal levels of the studied hormones were similar in the two groups. In both the treated patients and the control subjects, a statistically significant increase (p < 0.01) in LH, FSH, TSH and PRL levels was observed after GnRH/TRH administration. Comparing the respective areas under the LH, FSH, TSH and PRL response curves between the two groups did not present any statistically significant difference. These findings indicate that long-term therapy with diltiazem does not alter pituitary hormone secretion.     

The effects of naltrexone, an opioid receptor antagonist, on plasma LH levels in common carp (Cyprinus carpio L.)

Naltrexone-an opioid receptor antagonist, was administered intraperitoneally to sexually mature male and female common carp in the prespawning period, in order to investigate its effects on spontaneous or sGnRH-A-stimulated LH secretion. Naltrexone and sGnRH-A were injected at the same time. The possible involvement of a dopaminergic system in this process was studied in males pre-treated with pimozide (a dopamine receptor antagonist) 12 h before naltrexone and/or sGnRH-A administration. Blood samples for the analysis of carp LH concentrations were taken just before the injections and then after the injections, serial sampling during 24 h was performed. In male carp, naltrexone (500 or 5000 microg kg(-1)) decreased spontaneous LH release, but there were no effects of naltrexone on sGnRH-A-stimulated LH secretion. In males pre-treated with pimozide, a similar response to naltrexone injection (500 microg kg(-1)) as in pirnozide non-treated fish, was observed. The highest dose of naltrexone, 5000 microg kg(-1), significantly stimulated LH release, in response to sGnRH-A administration in pimozide pre-treated males. In female carp, contrary to males, naltrexone at a dose of 500 microg kg(-1), caused significant stimulation of spontaneous LH release. These data indicate that endogenous opioid peptides modify LH secretion in sexually mature carp. In males, they stimulate LH secretion, acting rather on the hypothalamic GnRH system and in females, opioids inhibit LH release by the influence on the dopaminergic system.     

Effect of dexamethasone on secretion of luteinizing hormone and testosterone in the boar

Eight adult, Yorkshire-Landrace crossbred boars were used to evaluate the effects of the synthetic glucocorticoid, dexamethasone (DXM) on the secretion of luteinizing hormone (LH) and testosterone. Four treatments of 4 d each were administered: 1) 2 ml i.m. of 0.9% (w/v) NaCl solution (control); 2) DXM (2 ml i.m. as a dose of 50 mug/kg body weight, every 12 h); 3) DXM plus gonadotropin releasing hormone (GnRH; 50 mug in 1 ml i.m. every 6 h); 4) 2 ml NaCl solution i.m. plus a single dose of 50 mug i.v. GnRH. Blood samples were collected twice daily from an indwelling jugular vein catheter for 3 d and at 15 min intervals for 12 h on the fourth day. DXM treatment resulted in lower (P M0.01) testosterone values in samples collected twice daily. More frequent sampling on Day 4 revealed that DXM reduced (P<0.01) the number of pulsatile increases of LH in plasma, although the individual mean pulse areas did not fiffer between the NaCl- and DXM-treated groups. This was associated with a decreased pulse frequency of testosterone (P<0.05). GnRH plus DXM treatment caused a significant elevation (P<0.05) in mean values as well as in the mean pulse area and in the total of the individual pulse areas of LH. Pulse area and mean concentrations of testosterone were also increased (P<0.01) when GnRH was given concurrently with DXM. Comparison of a single injection of GnRH when NaCl was being administered (Treatment 4) to one of the injections of GnRH (Day 4, 0800 h, Treatment 3) revealed a subsequently greater (P<0.01) pulse area in LH above base-line during DXM treatment (7.67 +/- 1.17 ng/ml) than during the NaCl (4.17 +/- 0.73 ng/ml) treatment period. This was reflected in a greater (P<0.01) pulse increase of testosterone following the LH pulse in boars treated with DXM. It is concluded that DXM treatment in the boar can reduce the pulse frequency of LH secretion, presumably by affecting GnRH secretion, but it has less effect directly on pituitary LH synthesis and release.     

Cortisol response and ovarian hormones in juvenile and cycling female Cebus monkeys: effect of stress and dexamethasone

We examined cortisol profiles in relation to ovarian hormones and their response to a repeated composite stressor with and without dexamethasone suppression. To evaluate the day-to-day changes in circulating cortisol relative to ovarian hormones, we subjected five adult female Cebus apella monkeys daily to restraint, sedation, transport to a neighboring room for femoral venipuncture, and return to the cage throughout the menstrual cycle. The cortisol response to the repeated stressor for blood collection, its relationship with the ovarian function, and the effects of dexamethasone were evaluated in six juveniles (18-24 months old) and five adult females in the luteal phase. Blood was sampled at time 0; then the monkeys received the vehicle and their blood was sampled again at 1, 2, 4, and 24 hr. This experiment was repeated 3 weeks later, with dexamethasone (i.m. 2 mg/Kg) injected instead of vehicle. Plasma aliquots were assayed for cortisol, progesterone, and estradiol. The results revealed that from middle infancy and throughout adulthood, hypercortisolism is the norm in female Cebus monkeys. The high cortisol values remained unchanged across the cycle despite the cyclic changes in estradiol and progesterone levels. Juvenile monkeys exhibited a higher cortisol response to stress than adults, and both juvenile and adult monkeys exhibited the typical suppression by dexamethasone. A rapid suppression of progesterone co-occurred in parallel with cortisol after dexamethasone injection in juvenile monkeys, suggesting that most circulating progesterone originates in the adrenals. In contrast, adult females exhibited an overincrement of progesterone levels, in parallel with a rise in cortisol, in response to the stressor, and this effect was exacerbated by dexamethasone. The findings suggest that hypercortisolism is insufficient to disrupt ovarian development toward a normal cyclical function, and that ovarian steroids have no influence on day-to-day circulating cortisol levels. On the other hand, the overincrement of progesterone levels induced by stress and/or glucocorticoids during the early luteal phase is unlikely to interfere with the development of this phase and implantation in this monkey species.     

Gonadotropin, prolactin and thyrotropin pituitary secretion after exogenous dehydroepiandrosterone-sulfate administration in normal women.

The effect of exogenous dehydroepiandrosterone-sulfate (DHAS) on luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin (PRL) and thyroid-stimulating hormone (TSH) pituitary secretion was studied in 8 normal women during the early follicular phase. The plasma levels of these hormones were evaluated after gonadotropin-releasing hormone (GnRH)/thyrotropin-releasing hormone (TRH) stimulation performed after placebo or after 30 mg DHAS i.v. administration. The half-life of DHAS was also calculated on two subjects; two main components of decay were detected with half-times of 0.73-1.08 and 23.1-28.8 h. The results show an adequate response of all hormones to GnRH or TRH tests which was not significantly modified, in the case of LH, FSH and PRL, when performed in the presence of high levels of DHAS. However, the TSH response to TRH was significantly less suppressed (p less than 0.05) (39%) after DHAS administration than during repeated TRH stimulation without DHAS (51%). The data support the hypothesis that DHAS does not affect LH, FSH and PRL secretion, while TSH seemed to be partially influenced.     

Pituitary luteinizing hormone (LH) and follicle-stimulating hormone (FSH) responses to gonadotropin-releasing hormone during the rat estrous cycle: an increased ratio of FSH to LH is secreted during the secondary FSH surge

The hormonal interactions required for the generation of a secondary surge of FSH on the evening of proestrus have not been clearly defined. The role of GnRH in driving a surge of FSH has been questioned by findings in previous studies. In the current study, gonadotropin secretion was measured from pituitary fragments obtained from rats at 0900 and 2400 h on each day of the estrous cycle. Pituitary fragments were perifused in basal (unstimulated) conditions or in the presence of GnRH pulses to determine whether a selective increase in basal release of FSH and/or an increase in the responsiveness to GnRH occurs during the secondary FSH surge. Each anterior pituitary was cut into eighths and placed into a microchamber for perifusion. Seven pulses of GnRH (peak amplitude = 50 ng/ml; duration = approximately 2 min) were administered at a rate of one per hour starting at 30 min. Fractions of perfusate were collected every 5 min and frozen until RIA for LH and FSH. The mean total amount of LH or FSH secreted during the hour interval following each of the last six pulses of GnRH (or the corresponding basal hour) was calculated. Analysis of variance with repeated measures indicated that the evening secretion of LH on proestrus (2400 h) dropped significantly (p less than 0.05) from a maximum on the morning of proestrus (0900 h), whereas the FSH secretion remained elevated at this time. Therefore, the ratio of FSH to LH secreted in response to GnRH pulses was highest during the secondary FSH surge and lowest on the morning of proestrus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Catecholamines and pituitary-function. V. Effect of low-dose dopamine infusion on basal and gonadotropin-releasing hormone stimulated gonadotropin release in normal cycling women and patients with hyperprolactinemic amenorrhea

To verify the role of dopaminergic mechanisms in the control of gonadotropin secretion in normal and hyperprolactinemic women, we examined the gonadotropin response to GnRH (100 micrograms i.v.) administration in both basal conditions and during low-dose dopamine (DA, 0.1 microgram/kg/min) infusion. Hyperprolactinemic women, either with microadenoma or without radiological signs of pituitary tumor, showed significantly enhanced LH and FSH responses to GnRH in comparison with normal cycling women. 0.1 microgram/kg/min DA infusion did not result in any appreciable suppression of serum gonadotropin levels but significantly reduced the LH and FSH responses to GnRH in both normal and amenorrheic hyperprolactinemic women. Although both LH and FSH levels remained higher in hyperprolactinemic patients than in normal women after GnRH, the gonadotroph's sensitivity to DA inhibition was normal in the hyperprolactinemic group, as both control subjects and patients with hyperprolactinemic showed similar per cent suppression of GnRH-stimulated gonadotropin release during DA. These data confirm that hypothalamic DA modulates the gonadotroph's responsiveness to GnRH. The increased LH and FSH responses to GnRH in hyperprolactinemic patients and their reduction during low-dose DA infusion seem to indicate that endogenous DA inhibition of pituitary gonadotropin release is reduced rather than enhanced in women with pathological hyperprolactinemia.     

Suppression of pulsatile luteinizing hormone secretion by gonadotrophin-releasing hormone antagonist does not affect episodic progesterone secretion or corpus luteum function in ewes.

Progesterone secretion has been observed to be episodic in the late luteal phase of the oestrous cycle of ewes and is apparently independent of luteinizing hormone (LH). This study investigated the effects of suppressing the pulsatile release of LH in the early or late luteal phase on the episodic secretion of progesterone. Six Scottish Blackface ewes were treated i.m. with 1 mg kg-1 body weight of a potent gonadotrophin-releasing hormone (GnRH) antagonist on either day 4 or day 11 of the luteal phase. Six ewes received saline at each time and acted as controls. Serial blood samples were collected at 10 or 15 min intervals between 0 and 8 h, 24 and 32 h, and 48 and 56 h after GnRH antagonist treatment and daily from oestrus (day 0) of the treatment cycle for 22 days. Oestrous behaviour was determined using a vasectomized ram present throughout the experiment. Progesterone secretion was episodic in both the early and late luteal phase with a frequency of between 1.6 and 3.2 pulses in 8 h. The GnRH antagonist abolished the pulsatile secretion and suppressed the basal concentrations of LH for at least 3 days after treatment. This suppression of LH, in either the early or late luteal phase, did not affect the episodic release of progesterone. Daily concentrations of progesterone in plasma showed a minimal reduction on days 11 to 14 after GnRH antagonist treatment on day 4, although this was significant (P < 0.05) only on days 11 and 13. There was no effect of treatment on day 11 on daily progesterone concentration, and the timing of luteolysis and the duration of corpus luteum function was unaffected by GnRH antagonist treatment on either day 4 or day 11. These results indicate that the episodic secretion of progesterone during the luteal phase of the oestrous cycle in ewes is independent of LH pulses and normal progesterone secretion by the corpus luteum can be maintained with minimal basal concentrations of LH.     

The role of cholecystokinin octapeptide (CCK-8) in regulating thyrotropin secretion in rats. In vivo studies

The effect of cholecystokinin octapeptide (CCK-8) on basal and TRH-stimulated secretion of TSH was investigated in 67 male Sprague-Dawley rats. Blood for TSH determinations was sampled by cannulation of right heart auricle in urethane narcosis before and four times during 60 minutes following CCK-8 administration. It was found that CCK-8 administered to the lateral brain ventricle at a dose of 0.5 microgram per animal caused a decrease in blood serum TSH concentration but did not change the response of TSH to TRH. Intravenous administration of CCK-8 at doses of 2 and 20 micrograms/kg had no effect on blood serum concentration of TSH.     

LH responses of female naked mole-rats, Heterocephalus glaber, to single and multiple doses of exogenous GnRH

To investigate possible differential pituitary secretion of LH in breeding and non-breeding female naked mole-rats, the LH responses to administration of exogenous GnRH were measured in 55 females from 20 captive colonies. Single doses of 0.1, 0.5 or 1.0 micrograms GnRH produced a significant rise in plasma LH concentrations 20 min after s.c. injection in breeding and non-breeding females at all doses (P less than 0.001). While at the highest dose of 1.0 microgram there was no difference in the LH response between breeding and non-breeding females, as the dose was lowered there was a progressive decline in the LH response in non-breeding females such that, at the 0.1 microgram dose, GnRH produced only a small, but significant, increase in plasma LH (1.3 +/- 0.2 to 2.9 +/- 0.5 mi.u./ml, N = 5) compared with breeding females (3.4 +/- 0.8 to 9.6 +/- 2.0 mi.u./ml, N = 6). The LH responses of the latter were not significantly reduced at the lower doses of GnRH. The apparent lack of sensitivity to low doses of exogenous GnRH in non-breeding females was reversed by 4 consecutive 1-h injections of 0.1 microgram, which produced a rise in LH from 1.2 +/- 0.2 to 9.0 +/- 0.2 mi.u./ml (N = 4), comparable to that of breeding females given a single injection of 0.1 microgram GnRH. These results suggest that the anterior pituitary in non-breeding female naked mole-rats is less sensitive to low doses of exogenous GnRH than in breeding females, possibly due to a lack of priming by endogenous GnRH. Therefore, the socially-induced block to ovulation in non-breeding female naked mole-rats may be due to inhibition of hypothalamic GnRH secretion.     

Potentiation by indomethacin of TRH-induced TSH secretion in the rat.

We have studied the effect of two inhibitors of prostaglandin synthesis on the basal and TRH-stimulated plasma TSH levels in the rat. Animals were injected sc daily with indomethacin 3 mg/0.5 ml) or aspirin (16--30 mg/0.5 ml) for 3 days. The plasma T4 and T3 were consistently lower in the indomethacin or aspirin groups than in the controls, while the basal TSH levels did not change. Indomethacin treatment significantly potentiated the TSH response to synthetic TRH (20 ng. iv) in intact and thyroidectomized rats. The pituitary TSH content was markedly increased by indomethacin, while hypothalamic TRH content did not change. In contrast, aspirin inhibited the TSH response to TRH in intact rats, when pituitary TSH content decreased significantly. No potentiation by aspirin of TRH-stimulated TSH response in the thyroidectomized rats was observed. The increased sensitivity of plasma TSH response to exogenous TRH in the indomethacin group is presumably due to higher pituitary TSH content than in the controls. The action of indomethacin appears to be mediated, at least in part, at the pituitary level. In addition, there is a dissociation between the action of indomethacin and the action of aspirin in the TSH response to TRH.     

Dual mechanisms of inhibition by dopamine of basal and thyrotropin-releasing hormone-stimulated inositol phosphate production in anterior pituitary cells. Evidence for an inhibition not mediated by voltage-dependent Ca2+ channels.

In primary cultures of anterior pituitary cells, dopamine inhibited basal and thyrotropin-releasing hormone (TRH)-stimulated inositol monophosphate, bisphosphate, and trisphosphate production. This inhibition by dopamine can be resolved into two distinct components. One of the components was rapid and already present after 10 s. The other was slower, starting after 1 min, and was mimicked by nimodipine, a dihydropyridine calcium channel antagonist. The effects of dopamine and nimodipine were not additive on both basal and TRH-stimulated inositol phosphate production. Furthermore, the dopamine inhibition in the presence of TRH was much higher than the inhibition induced by nimodipine. It is thus likely that calcium entry through voltage-dependent calcium channels triggers a positive feedback on TRH stimulation of phospholipase C. However, depolarizing concentrations of K+ or BAY-K-8644, a voltage-dependent calcium channel agonist, had no effect on inositol monophosphate and bisphosphate accumulation. Ionomycin, even at a very high concentration (10 microM), had only a slight and transient effect on inositol phosphate formation. In addition, these agents did not affect the TRH dose-dependent stimulation of inositol phosphate production. These results suggest that the intracellular calcium concentrations that we measured under basal and TRH-stimulated conditions are sufficient to allow the maximal activity of phospholipase C which can be obtained under these two experimental conditions. In contrast, any decrease in the intracellular calcium concentration by a dihydropyridine antagonist, suppression of extracellular calcium, or inactivation of a voltage-dependent calcium channel by long term depolarization with K+ decreased the phospholipase C activities measured under basal and TRH-stimulated conditions. From these data it can be concluded that dopamine inhibits inositol phosphate production by two distinct mechanisms. The slow dopamine-induced inhibition of TRH-stimulated inositol phosphate production which is mimicked by nimodipine is likely because of an inhibition of a voltage-dependent calcium channel. This is substantiated further by the fact that ionomycin (10 microM) was able to reverse the nimodipine inhibitions as well as this slow component of dopamine inhibition. The nature of the rapid inhibition of TRH-stimulated inositol phosphate production induced by dopamine, but not by nimodipine, remains to be determined. It is suppressed in the absence of extracellular Ca2+. This may suggest that this inhibition is related to blockade of non-dihydropyridine-sensitive Ca2+ channels.(ABSTRACT TRUNCATED AT 400 WORDS)     

Catecholamine inhibition of luteinizing hormone secretion in isolated pig pituitary cells

This study investigated the direct effect of catecholamines, epinephrine (EPI), and norepinephrine (NE) on basal and gonadotropin-releasing hormone (GnRH)-stimulated secretion of luteinizing hormone (LH) from dispersed pig pituitary cells in vitro. Pig pituitaries were dispersed into cells with collagenase and DNAase and then cultured in McCoy's 5a medium containing horse serum (10%) and fetal calf serum (2.5%) pretreated with dextran-coated charcoal for 3 days. EPI and NE did not affect basal LH secretion after 4 h of incubation. When pituitary cells were incubated with EPI or NE (1 microgram/ml) for longer than 30 min, GnRH-stimulated LH secretion was reduced. The degree of this reduction was dependent on EPI and NE, and a concentration of EPI and NE higher than 1 ng/ml and 100 ng/ml, respectively, was needed. L-isoproterenol, a nonselective beta-agonist, also inhibited the LH response to GnRH. Propranolol, a beta-antagonist, blocked the inhibitory effect of EPI, whereas phentolamine, an alpha-antagonist, had no effect. These results suggest that catecholamines, acting by a beta 2-adrenergic receptor, may play a role in the control of the porcine pituitary gonadotrope's response to GnRH.     

Social suppression of reproduction in male naked mole-rats, Heterocephalus glaber

To investigate possible anatomical and endocrine differences between breeding and non-breeding male naked mole-rats, 113 animals from 24 captive and 4 wild colonies were studied. While breeding males had larger reproductive tract masses compared to non-breeders relative to body mass (P less than 0.01), spermatogenesis was active in all of the non-breeding males examined histologically (n = 9) and spermatozoa were present in the epididymides. Compared with non-breeders, breeding males had significantly higher urinary testosterone concentrations (mean +/- s.e.m.: 23.8 +/- 2.3 vs 5.2 +/- 1.4 ng/mg Cr respectively; P less than 0.001), and plasma LH (10.7 +/- 1.7 vs 5.0 +/- 0.8 mi.u./ml respectively; P less than 0.01). Single doses of 0.1, 0.5 or 1.0 microgram GnRH produced a significant rise in plasma LH concentrations 20 min after s.c. injection in breeding and non-breeding males at all doses (P less than 0.001). However, there were differences in the magnitude of the LH response following administration of GnRH between breeding and non-breeding males, with non-breeding males showing a dose-response and having lower plasma LH concentrations 20 min after a single injection of 0.1 or 0.5 microgram (P less than 0.05), but not 1.0 microgram, GnRH. This apparent lack of pituitary sensitivity of non-breeding males to single doses of exogenous GnRH was reversed by 4 consecutive injections of 0.5 microgram GnRH at hourly intervals, suggesting that the reduced sensitivity may be the result of insufficient priming of the pituitary by endogenous GnRH. These results indicate that, despite the fact that non-breeding males were apparently producing mature gametes, clear endocrine deficiencies existed in male naked mole-rats.     

Central, stereoselective receptors mediate the acute effects of opiate antagonists on luteinizing hormone secretion

Although a central site of acute opiate action in regulating luteinizing hormone (LH) secretion has been suggested by the ability of centrally implanted opiate antagonists to increase LH levels, opiate antagonists are lipophilic and could influence the pituitary in situ. Also, the physiological significance of opiate receptor blockade with antagonists rests on the assumed, but untested, stereoselectivity of these receptors. Therefore, a lipophobic quaternized derivative of naltrexone (MRZ 2663-Naltrexone methobromide) and dextro- (+) and levo- (-) stereoisomers of naloxone were used to study the site- and stereoselectivity of gonadotropin responses to opiate antagonists in vivo. Male rats were injected intracerebroventricularly (icv) or intravenously (iv) with the quaternary or tertiary congeners of naltrexone and subcutaneously (sc) with (-) or (+)-naloxone. Rats injected icv with 20 ug of quaternary naltrexone displayed significant increases in serum luteinizing hormone (LH). The onset of the response was rapid with serum LH levels being significantly elevated 15 minutes after the injection and returning to basal levels 30 minutes later. Rats injected iv with 10 mg/kg of quaternary naltrexone failed to show significant LH responses. Rats injected either centrally or periphally with equivalent doses of tertiary naltrexone showed LH responses that were similar to those found in animals injected icv with quaternary naltrexone. As little as 0.5 mg/kg of (-)-naloxone resulted in significant elevations in serum LH that were higher than those elicited by up to 10 mg/kg of (+)-naloxone, indicating that this effect of naloxone is stereoselective. These data support the argument that opioids can acutely modulate LH secretion through actions at stereoselective opioid receptors in the central nervous system.     

Gonadotrope function in ovariectomized ewes actively immunized against gonadotropin-releasing hormone (GnRH)

The gonadotrope cells of the ovine anterior pituitary were insulated from hypothalamic inputs by imposing an immunologic barrier generated by active immunization of ovariectomized ewes against gonadotropin-releasing hormone (GnRH) conjugated to keyhole limpet hemocyanin (KLH) through a p-aminophenylacetic acid bridge. All GnRH-KLH animals immunized developed titers of anti-GnRH that exceeded 1:5000. The antisera were specific for GnRH and cross-reacted with GnRH agonists modified in position 10 to an extent that was less than 0.01%. Ewes actively immunized against GnRH-KLH displayed levels of basal and GnRH agonist-induced gonadotropin secretion that were markedly lower (p less than 0.05) than comparable parameters in ewes actively immunized against KLH. In contrast, basal and thyrotropin-releasing hormone (TRH)-induced prolactin (PRL) secretion were not compromised by active immunization. Immunization against the GnRH-KLH conjugate, but not KLH alone, prevented expression of the positive feedback response to exogenous estradiol (E2). Pituitary stores of immunoactive luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were significantly (p less than 0.001) reduced in ewes immunized against GnRH-KLH but stores of PRL were not affected by such immunization. Further, the biopotency of the residual LH stores in tissue of animals from the anti-GnRH group was significantly (p less than 0.05) lower than LH biopotency in anti-KLH animals. Serum levels of LH in anti-GnRH ewes were restored by circhoral administration of a GnRH agonist that did not cross-react with the antisera generated. Pulsatile delivery of GnRH agonist in anti-GnRH ewes significantly (p less than 0.05) elevated serum LH within 48 h and reestablished LH levels comparable to anti-KLH ewes within 6 days of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Annual cycle in LH and testosterone release in response to GnRH challenge in male woodchucks (Marmota monax)

Testosterone and LH concentrations were determined in serum samples obtained before and 15 min after injections of GnRH (1 microgram kg-1) administered at 4-7 week intervals over 20 months to groups of male woodchucks (n = 6-7) born and maintained in Northern Hemisphere (boreal) versus Southern Hemisphere (austral) simulated natural photoperiods, beginning at 18-24 months of age. Nadir and peak unstimulated testosterone (0.1 +/- 0.01 and 7.0 +/- 0.1 ng ml-1, respectively) and LH (0.8 +/- 0.2 and 8.1 +/- 1.1 ng ml-1, respectively) concentrations did not differ in boreal versus austral males. In the five boreal and five austral males that were confirmed to be photoentrained, basal (pre-GnRH) concentrations of LH and testosterone were lowest in summer, increased simultaneously in late autumn or early winter, and declined in the spring. GnRH stimulated some LH release throughout the year except for a 1-4 month period in the summer. The initial annual increase in the LH response to GnRH occurred in early autumn, and in 17 of 20 cycles it occurred 1-2 months before the initial increase in basal LH was detected. In the three free-running males not entrained to the photoperiod, the endocrine patterns were similar but were advanced by several months. The results demonstrate that in woodchucks there is a late autumn increase in LH secretion associated with the onset of testicular recrudescence, and an early autumn increase in pituitary response to GnRH before a detectable increase in serum testosterone.     

Gonadotropin secretion following pernasal stimulation with synthetic gonadotropin releasing hormone (GnRH) and a highly effective GnRH-analog in healthy men and prepubertal boys]

Potent long acting analogs of GnRH are of great interest especially in view of pernasal (p.n.) treatmen of hypogonadism of hypothalamic origin and of cryptorchidism. To find the necessary p.n. dosage of such a substance, serum LH and FSH were measured in 6 normal adult human males after p.n. application of various doses of D Leu6-des-Gly10-GnRH ethylamide. 50 microgram of the GnRH analog were necessary to obtain increased serum gonadotropins over a period of at least 8 hours. By repeated p.n. application of 200 microgram of synthetic GnRH every 2 hours in 6 normal adult males a considerable increase of serum gonadotropins could be demonstrated as well. Pernasal application of 200 microgram GnRH repeated at an interval of 1 hour in 3 cryptorchid boys produced a distinct increase of the serum gonadotropins. The intraindividual comparison of 200 microgram GnRH and 20 microgram of the GnRH analog in one boy showed equivalent net increases of the gonadotropins. With the analog the gonadotropin increase lasted for about 6 hours.