Pulsatile LHRH Research Articles

A Role for Norepinephrine in the Control of Puberty in the Female Rhesus Monkey,Macaca Mulatto*

The onset of puberty in female rhesus monkeys is characterized by increases in pulsatile LHRH release. In this study we have tested the hypothesis that changes in input to the LHRH neurosecretory system from noradrenergic neurons contribute to this pubertal increase in LHRH release. In the first experiment, the ability of the LHRH neurosecretory system of prepubertal (12-20 months of age, no signs of puberty evident), early pubertal (24-30 months, premenarchial), and midpubertal (30-45 months, postmenarchial but prior to first ovulation) monkeys to respond to alpha 1-adrenergic stimulation was tested. LHRH release in the stalk-median eminence of conscious monkeys was measured using an in vivo push-pull perfusion method. During push-pull perfusion, perfusates were collected continuously in 10-min fractions, and the alpha 1-adrenergic stimulant methoxamine (MTX, 10(-8), 10(-5) M) or vehicle was infused through the push cannula for 10 min at 90 min intervals. LHRH levels in perfusates were estimated by RIA. Monkeys in all three age groups responded to MTX with significant increases in LHRH release, with the response of the prepubertal group being significantly greater than that of the older age groups. The results indicate that alpha 1-adrenergic receptors are present and functional prior to puberty. In the second experiment, norepinephrine (NE) release in perfusates collected from monkeys in the three age groups was measured by HPLC with electrochemical detection. NE release increased significantly from the pre- and early pubertal to the midpubertal stage. The enhanced sensitivity of prepubertal monkeys to MTX may be due to the absence of high levels of endogenous NE, which results in a situation similar to denervation hypersensitivity. During the early pubertal stage, increases in input from noradrenergic neurons to the LHRH neurosecretory system may occur, thereby resulting in increases in LHRH release, since early pubertal monkeys are highly sensitive to alpha-adrenergic input. Therefore, we propose that the increase in NE release during puberty contributes to the developmental increase in LHRH release.

Initiation of spermatogenesis and successful in vitro fertilization in an infertile male with panhypopituitarism; superiority of pulsatile LH-RH over gonadotropins?; a case report

This case report describes an infertile male patient with panhypopituitarism, presumably caused by traumatic breech delivery. Previous hMG/hCG treatment had failed to induce spermatogenesis. Initiation of the production of motile and morphological normal sperm, despite persisting significant oligozoospermia was established with s.c. pulsatile LH-RH treatment. Spermatogenesis could be maintained with i.m. hCG injections bi-weekly. Later, fruitful in vitro fertilization (IVF) resulted in the birth of a healthy daughter.

Neuropeptide Y Potentiates Luteinizing Hormone (LH)-Releasing Hormone-Stimulated LH Surges in Pentobarbital-Blocked Proestrous Rats*

Recent evidence suggests that hypothalamic neurosecretion of neuropeptide Y (NPY) may be required for the preovulatory LH surge in female rats. Results of immunoneutralization and portal blood collection studies have suggested that NPY may serve to enhance the response of gonadotropes to the stimulatory action of LHRH. To directly test this hypothesis, the effects of NPY on LHRH-stimulated LH secretion were assessed in proestrous rats that were anesthetized with pentobarbital (PB) to block endogenous LHRH neurosecretion. Female rats were fitted with atrial catheters on diestrus. On proestrus, hourly blood samples were collected from 0900-2100 h. At 1330 h, rats received PB (40 mg/kg BW) or saline. Every 30 min from 1400-1800 h, PB-treated rats received iv pulses of LHRH (15, 150, or 1500 ng/pulse) or saline along with concurrent pulses of NPY (1 or 10 micrograms/pulse). Plasma samples were analyzed by LH RIA. In PB-treated rats receiving vehicle pulses only, LH surges were completely blocked. Pulsatile LHRH treatments at 15, 150, and 1500 ng/pulse produced subphysiological, physiological, and supraphysiological LH surges, respectively. Simultaneous administration of NPY pulses with 15 ng/pulse LHRH produced significant dose-related potentiations of LHRH-stimulated LH surges (P less than 0.0001). Administration of NPY pulses with 150 ng LHRH/pulse also significantly enhanced LHRH-induced LH surges (P less than 0.05). NPY RIA of plasma confirmed NPY increments after treatments. These results demonstrate that NPY administration can potentiate pituitary responsiveness to LHRH stimulation, and are consistent with the hypothesis that one function of NPY is to operate as a neurohormonal modulator at the level of the gonadotrope during generation of the preovulatory LH surge.

Exposure to estradiol impairs luteinizing hormone function during aging

The loss of ovulatory cyclicity in many mammals is caused by changes in the hypothalamic-pituitary (H-P) control of the preovulatory luteinizing hormone (LH) surge. This work evaluated the anterior pituitary (AP) component of the H-P axis by determining the ability of perifused AP to release LH following sustained but pulsatile LHRH stimulation. The normal dual discharge profile of LH was affected by age. The first hour of the response, unaffected by cycloheximide, was similar in 5–6 month-old (mature), 12–13-month-old (declining litters) and 16–18-month-old (irregularly cycling) mice. The remaining protein synthesis-dependent part of the response was reduced in the 16–18 and 22–24-month-old (anestrus) mice. The role of estradiol (E2) in AP aging was further tested as AP from ovariectomized (OVXed) mice, deprived of E2 since puberty, responded as well as the mature proestrous group. In contrast, aged mice subjected to long-term E2 exposure (cycling or OVXed plus E2 replacement) failed to produce the dual response pattern. Since alterations in LH response occurred during the protein-dependent phase, synthetic processes that involve packaging and transport of stored LH, or the production of new LH, may be affected by age. Furthermore, E2 is a major factor in altering LH function and appears to act before middle age.

Autonomous FSH synthesis in vitro in anterior pituitary glands and grafts from female rats

When pituitary glands from intact female, but not from ovariectomized rats, are incubated for 8 h in medium TC199 without further additives, FSH is synthesized. This LHRH-independent (or autonomous) FSH synthesis is prevented when bovine follicular fluid (bFF) is added to the incubation medium. Results from preliminary experiments, however, indicate no clear autonomous FSH synthesis after long-term absence of LHRH. To investigate the regulatory mechanisms involved in autonomous FSH synthesis and release, pituitary glands (exposed to endogenous LHRH) and pituitary grafts (not exposed to endogenous LHRH) from intact and ovariectomized rats were incubated for 8 h in medium TC199. Total FSH content (FSH released plus FSH remaining in the tissue) was compared with that in non-incubated glands or grafts, giving an indication of FSH synthesis. In addition, some of the animals were given LHRH pulses for 40 h before incubation. When pituitary tissue was taken from intact female rats, FSH synthesis occurred in the animals' own glands and in grafts from LHRH-pretreated rats. No FSH synthesis was seen in ovariectomized rats with or without pretreatment with bFF and/or LHRH. However, when ovariectomized rats had been pretreated with oestrogen, FSH synthesis was measured in vitro after pulsatile LHRH treatment in vivo. The results indicate that autonomous FSH synthesis in vitro is dependent upon previous (in vivo) exposure of the glands to both oestrogen and LHRH.

The physiological significance of pulsatile LHRH secretion in man: gonadotrophin responses to physiological doses of pulsatile versus continuous LHRH administration

This study tested whether pulsatile LHRH stimulation of the pituitary is required for normal gonadotrophin secretion in man. Four men with idiopathic hypogonadotrophic hypogonadism (IHH) and presumed endogenous LHRH deficiency were taken off all hormonal replacement for 5-6 weeks, then 5 micrograms LHRH was administered every 2 h for 1 week in order to prime pituitary gonadotrophin responsiveness. A physiological dose of LHRH (10 micrograms every 2 h) was then administered in both pulsatile and continuous regimens, in varying order, to each man. Pulsatile LHRH was capable of stimulating LH (as measured by bioassay) and FSH secretion, while continuous administration of LHRH was not. Serum LH, measured by RIA and bioassay, and FSH and free alpha-subunit levels, measured by RIA, increased significantly (P less than 0.05) over pretreatment levels during pulsatile LHRH administration. In contrast, bioactive LH and immunoactive FSH did not change significantly compared to pretreatment values during continuous infusion of the same total LHRH dose, although immunoactive LH and free alpha-subunit levels did increase significantly (P less than 0.05). The ratio of LH bioactivity to immunoactivity was significantly lower during the continuous compared to pulsatile LHRH regimen (P less than 0.001). Similar serum LHRH levels were achieved during pulsatile and continuous infusions. Serum testosterone and oestradiol levels did not increase significantly from pretreatment levels during either regimen of LHRH administration. It is concluded that a pulsatile LHRH signal pattern is essential for normal pituitary gonadotrophin secretion in men with IHH. Continuous infusion of a physiological dose of LHRH, which produced serum LHRH levels which were indistinguishable from those found during pulsatile administration, failed to stimulate FSH or bioactive LH secretion.

Infusion of Neuropeptide Y into the Stalk-Median Eminence Stimulatesin VivoRelease of Luteinizing Hormone-Releasing Hormone in Gonadectomized Rhesus Monkeys*

Studies in the rat and rabbit indicate that facilitatory effects of neuropeptide Y (NPY) as well as norepinephrine (NE) on LH and LHRH release are dependent on the presence of the ovarian steroid estrogen. However, we have previously found the NE and an alpha-1-adrenergic agonist are both stimulatory to pulsatile LHRH release in ovariectomized rhesus monkeys. In the present experiment the effects of NPY on LHRH release were examined in conscious monkeys using a push-pull perfusion method. Twelve gonadectomized monkeys (8 females and 4 males) were used. Perfusate samples from the stalk-median eminence (S-ME) were obtained through a push-pull cannula at 10-min intervals for 12 h, and the amount of LHRH in samples were determined with RIA. NPY dissolved in a modified Krebs-Ringer phosphate buffer solution at concentrations of 10(-8), 10(-7), 10(-6), and 10(-5) M was directly infused into the S-ME through the push cannula for 10 min at 90-min intervals. Vehicle was infused as a control. Since sex differences in LHRH response to NPY were not present, data from males and females were combined for analysis. NPY infusion into the S-ME stimulated LHRH release in a dose-dependent manner (P less than 0.001). The peak LHRH responses (mean +/- SEM) to NPY at different concentrations were: 10(-8) M = 2.1 +/- 0.4 pg/ml; 10(-7) M = 2.6 +/- 0.5 pg/ml; 10(-6) M = 6.5 +/- 1.1 pg/ml; 10(-5) M = 15.1 +/- 2.9 pg/ml, whereas to vehicle 0.37 +/- 0.17 pg/ml. All NPY doses tested were significantly effective as compared to vehicle (P less than 0.01). The LHRH response to 10(-6) M was greater (P less than 0.01) than that of 10(-8) M or 10(-7) M, and the response to 10(-5) M was greater (P less than 0.01) than that of all lower doses. The results indicate that NPY infusion into the S-ME elicits the release of LHRH in vivo in a dose-dependent manner in the monkey. The data further suggest that LHRH neurons and/or neuroterminals in the monkey are responsive to NPY stimulation in the absence of gonadal steroids. It is concluded that in addition to NE, NPY is an important regulator of pulsatile LHRH release in the nonhuman primate.

The alpha-1-adrenergic neuronal system is involved in the pulsatile release of luteinizing hormone-releasing hormone in the ovariectomized female rhesus monkey.

It has been postulated that catecholamines are integral to the control of LHRH release. In the present study, the roles of adrenergic and dopaminergic receptors in the control of pulsatile LHRH release are examined. The effects of prazosin (an alpha 1-antagonist), rauwolscine (an alpha 2-antagonist), propranolol (a beta-antagonist), haloperidol (a dopamine antagonist), SCH23390 (a D1 antagonist), and LY163502 (a D2 agonist), on in vivo LHRH release in the stalk-median eminence were tested in ovariectomized female rhesus monkeys using push-pull perfusion. Prazosin caused a significant suppression of the LHRH release. This was primarily due to a significant suppression of LHRH pulse amplitude, but not pulse frequency, i.e. the interpulse interval was not affected by the administration of prazosin. In contrast to prazosin, none of the other adrenergic or dopaminergic drugs had significant effects on LHRH release. We conclude from these results that (1) the stimulatory effects of norepinephrine (NE) and/or epinephrine on pulsatile LHRH release are mediated by alpha 1-adrenergic receptors but not alpha 2- or beta-adrenergic receptors, and (2) dopaminergic receptors do not appear to be involved in pulsatile LHRH release in ovariectomized rhesus monkeys.

Role of Neuropeptide Y in Reproductive Functiona

NPY acts both at the hypothalamus and the anterior pituitary gland to modulate reproductive hormone secretion. Within the hypothalamus, NPY stimulates LHRH secretion in the presence of physiological levels of estrogen and suppresses pulsatile LHRH release following ovariectomy. Intracerebroventricular injection of NPY antiserum blocks or delays the LH surge in steroid-primed ovariectomized rats, thereby adding support for a physiological role of NPY in the neuroendocrine events preceding ovulation. Blockade of alpha 2 adrenergic receptors decreases NPY-stimulated LH release in steroid-primed rats implying a potential noradrenergic mediation of NPY activity. Physiological levels of progesterone do not augment, and may actually suppress NPY-induced LHRH secretion in vitro from median eminences obtained from estrogen-primed ovariectomized rats. The physiological role of progesterone, if any, in modulating NPY effects on LHRH release remains to be determined. Little, if anything, is known about the NPY receptor in the median eminence or the intracellular mechanisms which transduce the NPY signal into activation of LHRH release in estrogen-treated ovariectomized rats although translocation of intracellular calcium is required. Equally puzzling is the mechanism of desensitization of the LHRH-releasing mechanisms of the median eminence of ovariectomized rats or the specific site of NPY suppression of pulsatile LHRH secretion. NPY is released into the hypothalamo-hypophysial portal circulation and this appears correlated with LHRH secretion before the LH surge. NPY affects LH and FSH release from anterior pituitary cells in vitro and enhances LHRH-induced LH secretion. Taken together, the studies described above suggest an important physiological role for NPY as a modulator of neuroendocrine activity which culminates in the preovulatory surge of LH.

Treatment with pulsatile luteinizing hormone-releasing hormone modulates folliculogenesis in response to ovarian stimulation with exogenous gonadotropins in patients with polycystic ovaries

Combined treatment with pulsatile LH-RH and hMG, given to eight patients who had anovulation associated with PCO and resistant to CC, significantly reduced the number of large follicles induced by hMG alone. A direct effect of pulsatile LH-RH on the ovary is postulated. This combined treatment eased the problems of multifollicular development, thereby increasing efficiency and reducing complications in patients with PCO stimulated by gonadotropins.

Effect of pulsatile luteinizing hormone — releasing hormone administration on pituitary — gonadal function in elderly man

The effect of short-term pulsatile LHRH administration was studied in 8 healthy subjects ranging from 60 to 81 yr to see if the decrease of pituitary gonadal function could be in part due to changes in the discharge of LHRH from the hypothalamus. Gonadotropin and testosterone (T) secretion was evaluated two weeks before and during LHRH (122-160 ng/kg bw every 120 min sc) infusion. In addition, a bolus dosage of LHRH (50 mu iv) was given both at the beginning and at the end of pulsatile LHRH administration in order to test gonadotrophs sensitivity. A significant increase in gonadotropin levels from day 0 to day 4 was found, and was followed by a subsequent decrease from day 7 to day 14. A slight significant increase in T levels was observed during LHRH administration (p less than 0.01). LH pulses were identified in 5 out of 8 subjects on day 0. On day 14, all the exogenous LHRH pulses were followed by significant LH bursts. There was not a significant decrease in the pituitary LH responsiveness to LHRH test from day 0 to day 14. Our study seems to indicate that pituitary - gonadal unit in normal elderly men can be modulated by pulsatile administration of LHRH. A pulse frequency of LHRH which is probably similar to the physiological one, could induce a slight increase in T levels via qualitative changes in LH activity. We can assume that clinical changes in gonadal activity might also be connected to some disturbances in endogenous LHRH pulsar.

The Use Of Mouse Pituitary Fragments To Study Lh Secretion

This work evaluated a perifusion system for studying LH secretion from the anterior pituitary (AP) of female mice. Pituitary fragments were challenged with LHRH, and the effluents assayed for LH. In general, the tissue exhibited augmented release to repeated stimulation. In the dose-response study, the amount of LHRH required to produce maximum and half maximum responses dropped almost 10 fold by the 3rd stimulus. In response to various pulse frequencies LH release increased with the frequency of the 100 nM LHRH dose, but the tissue became refractive to constant nonpulsatile stimulation. Other preparations, subjected to high-frequency 10 nM LHRH pulses, released LH in two distinct episodes. All but the first hour of the response was blocked by cycloheximide, confirming the role of protein synthesis in the sustained release of LH. By varying both the pulse frequency and amplitude, a LHRH protocol was found that produced a proestrous-like surge. Lastly, rat and mouse tissues responded similarly to pulsatile LHRH, verifying their similar LH function during the preovulatory period. These studies demonstrate that the perifusion technique can be used for studying LH secretion in the mouse. Its application to other mouse-oriented studies is planned.

Administration pulsatile de la LH-RH: Applications diagnostiques et therapeutiques

Hypothalamic hypogonadotropic hypogonadism (HHH), a disorder occurring in both sexes, is characterized by a partial or complete inability to synthesize and/or release LH-RH from the hypothalamus which result in absence or defects of amplitude and frequency of gonadotropin secretion. Long term substitution by pulsatile exogenous LH-RH usually result in complete normalization of both pituitary and gonadic hormones. Such a treatment allows differentiation between hypothalamic and pituitary causes of hypogonadotrophic hypogonadism. Ovulation and fertility can be achieved in most of women with hypothalamic amenorrhea treated with pulsatile LH-RH using i.v. bolus doses of 25–100 ng/kg at 1–2 h intervals. In opposite LH-RH therapy yields inferior results to human menopausal gonadotropin (hMG) in chronic anovulatory patients with persistent LH secretion or polycystic ovary syndrome (PCOS) as shown by one randomized and several non-controlled studies. Successful pulsatile LH-RH treatment following a 2 months LH-RH analog suppression in PCOS previously refractory to LH-RH alone represents a new promising approach. The majority of men with complete HHH begin to produce sperm only after 1 year of therapy. Both the testicular volume and the mean sperm concentrations were below the normal values after 2 years of treatment in spite of normalization of testosterone, LH and FSH levels. Pulsatile LH-RH does not seem significantly improve the treatment of infertile HHH men compared to hMH/hCG.

Prolactin secretion in idiopathic hypogonadotropic hypogonadism during pulsatile luteinizing hormone-releasing hormone long-term administration

Recent data seem to suggest that LHRH may be involved in the modulation of PRL secretion. We studied the PRL pattern in 9 males (age range 18-38 yr) with idiopathic hypogonadotropic hypogonadism (IHH) before and during long-term pulsatile LHRH therapy (120-160 ng/kg bw every 120 min sc) in order to evaluate variations in the spontaneous PRL secretion or LHRH-induced presence of PRL pulse. LH, FSH and PRL secretion was evaluated every 15 min for 3 h on day 0, day 30 and days 90-150. Before and during LHRH therapy PRL 24-h integrated concentration (IC) and gonadotropin or PRL response to LHRH test (50 micrograms iv/bolus) were evaluated. On day 0 spontaneous PRL pulses were found in 2 IHH patients. On day 30 PRL pulses were found in 4 cases. On days 30-90 PRL pulses were sporadically concomitant with LHRH-induced LH pulses. Mean PRL levels and 24-h IC of PRL were found to be significantly (p less than 0.05) increased during pulsatile LHRH administration. A significant positive (p less than 0.01) correlation was observed between testosterone and PRL levels during LHRH therapy. When compared to a significant LH response to LHRH iv bolus, no modification of PRL secretion was found. The present study did not show any relationship between LHRH administration and PRL secretion. It might be hypothesized that LHRH does not play a determinant role in PRL secretion and does not seem to modulate PRL secretory pattern in IHH males.

Pulsatile LHRH therapy in patients with oligozoospermia and disturbed LH pulsatility

Pulsatile administration of LHRH can drive the pituitary to secrete LH and FSH in a pattern that closely mimics the physiological pattern of the hypothalamic-pituitary-gonadal axis. As there is evidence that infertility in some men is due to dysfunction of this axis, 14 men with reported infertility of more than 2 years duration were treated by long-term pulsatile LHRH therapy. They were 24-42 years of age, with variable degrees of oligozoospermia, elevated FSH levels but normal LH and testosterone levels. The number of endogenous LH pulses/24 h was less than eight in all 14 subjects. The degree of testicular damage was assessed semi-thin sections prepared from biopsies of both testes. Scores for spermatogonia per seminiferous tubule (SPT) were calculated from the actual number of Ad-spermatogonia/tubule. Patients were grouped according to sperm density and SPT score (groups I-III). Pulsatile LHRH therapy was administered by means of a portable infusion pump; 4 micrograms LHRH were administered subcutaneously every 120 min for a period of 6 months. This treatment restored the normal pattern of LH secretion to 12 LH pulses/24 h in all patients. A statistically significant decrease of mean FSH levels to normal, and an increase of mean LH levels was observed in most of the 14 patients. Testosterone values did not change in any group. Marked improvement of the sperm count was observed in eight out of 14 patients (groups I and II) and three pregnancies were reported during the treatment periods. These results suggest that some states of male infertility are due to hormonal dysregulation and that these patients may benefit from pulsatile LHRH therapy.

Neuropeptide-Y suppresses pulsatile secretion of luteinizing hormone in ovariectomized rats: possible site of action.

The hypothesis that neuropeptide-Y (NPY) suppresses pulsatile LH secretion in ovariectomized (OVX) rats was examined. Rats were bilaterally OVX and 6 weeks (Exp 1) or 2 weeks (Exp 2) later a stainless steel cannula was implanted in the third cerebral ventricle (3V). Seven to 10 days later, an intraatrial cannula was inserted. The next day, a blood sample was withdrawn, and each conscious unrestrained animal received a 3V injection of synthetic porcine NPY (5 or 0.5 micrograms/2 microliters saline) or vehicle in Exp 1. Blood samples were taken every 10 min for 2 h and centrifuged, and the plasma was analyzed for LH by RIA. In Exp 2, OVX rats received a 3V injection of NPY (5 micrograms/2 microliters) or vehicle. Blood samples were taken before and 60 min after injection. At 60 min, LHRH (10 ng/100 g BW) was injected iv, and blood was withdrawn 10, 20, 60, and 120 min later. NPY caused a dramatic dose-related reduction in the pulsatile release of LH compared to that in vehicle-treated rats. The 5.0-micrograms dose of NPY significantly reduced LH pulse frequency (P less than 0.05), pulse amplitude (P less than 0.01), and trough levels (P less than 0.01) compared to those in saline-injected controls. The lower dose of NPY (0.5 micrograms) significantly decreased the mean LH levels throughout the 2-h sampling period and slightly, though not significantly, the pulse frequency. Administration of LHRH increased plasma LH levels by 124% in control animals and by 1239% in NPY-injected rats. The results of these studies indicate that the suppressive effects of NPY on pulsatile LH release appear to be exerted through inhibition of pulsatile LHRH secretion from the hypothalamus.

129 PUBERTY CHANGES THE CONADOTROPIN RESPONSE TO ANLOXONE INFUSION

Naloxone, an opioid antagonist, increases LH/FSH blood levels in adults. The absent response in prepuberty may be caused by an insensitive, unstimulated pituitary. Therefore we studied LH/FSH secretion during naloxone infusion before and after LHRH priming. Protocol: three prepubertal boys aged 13.1-14.6 yrs (BA 10.4-12.3), Testosterone (T) 0.4-0.9 nmol/1, received LHRH 20 μg/1.7m2 every 90 min iv during 42 hrs. Before as well as 7 days after pulsatile LHRH treatment naloxone was infused iv from 10.00-13.00h 2 mg/-1.7m2/h. At 13.00h a LHRH test was performed. LH and FSH was measured from 9.00-15.00h at 15 min intervals. In 2 pts the study was repeated in a pubertal stage (G3).Results: in all three prepubertal boys naloxone did not elicit an increase of LH or FSH, neither before nor after LHRH priming, while the LH and FSH response to the LHRH test had distinctly increased after LHRH priming. In the 2 pubertal boys basal LH and FSH were within the same range; T was 4.5 and 13 nmol/l. Naloxone induced a clear LH increase with two LH pulses only in the boy with a T of 13 nmol/l, before as well as after LHRH priming.Conclusion: naloxone cannot induce a LH/FSH increase in prepuberty even not after LHRH priming; in puberty an increase can be elicited. Therefore the opioids take no major part in the LHRH “intrinsic restraint” during prepuberty, but play a role in the sex steroid negative feedback, which becomes operative during puberty.

Norepinephrine is a possible neurotransmitter stimulating pulsatile release of luteinizing hormone-releasing hormone in the rhesus monkey.

The hypothesis that norepinephrine (NE) plays a facilitatory role in controlling the pulsatile release of LHRH was tested with a modified push-pull perfusion technique in conscious rhesus monkeys. The in vivo LHRH release in perfusate samples collected from the stalk-median eminence of ovariectomized females was pulsatile and synchronous with pulsatile LH release. Catecholamines measured in aliquots of perfusate samples revealed that in vivo NE release was also pulsatile and was synchronous with LHRH release. Local infusion of NE or methoxamine (an alpha 1-adrenergic stimulant) through a push cannula stimulated LHRH release, while iv injection of prazosin (an alpha 1-adrenergic blocker) suppressed LHRH release. It is concluded that NE is a possible neurotransmitter stimulating pulsatile LHRH release.

Hypogonadotropic hypogonadal men respond less well to androgen substitution treatment than hypergonadotropic hypogonadal men.

This research asked whether androgen substitution therapy is as efficacious in hypogonadotropic hypogonadal men as in hypergonadotropic hypogonadal men. Erotosexual functions of two groups of six men of each diagnostic category were compared after 5-6 years of continuous androgen treatment. Treatment regimen was the same in both groups: Parenteral testosterone esters 250 mg/2 weeks. No difference was found in erectile and ejaculatory potency, but the number of sexual acts and scores of subjective quality of sexual acts, sexual excitement, and frequency of sexual thoughts and of nonsexual parameters as vigor, fatigue, anxiety were more negative in the hypogonadotropic men. The most obvious difference between the two groups is the value of LH/FSH and presumably of LHRH. Hypogonadotropic hypogonadal men may be better treated with gonadotropins (or with pulsatile LHRH, when the hypophysis is intact) than with androgens.

Effect of Pulsatile Infusion of Progesterone on thein VivoActivity of the Luteinizing Hormone-Releasing Hormone Neural Apparatus of Awake Unrestrained Female and Male Rabbits*

Eight female and eight male New Zealand White rabbits were outfitted with push-pull cannulae aimed at the tuberal region of the hypothalamus and were used in 19 perfusion experiments. Animals were treated under 2 conditions: a control condition in which female (n = 4) and male (n = 4) rabbits were perfused only with artificial medium for 5-9 h, and an experimental condition in which female (n = 4) and male (n = 5) rabbits were subjected to perfusion with artificial medium, followed by 6 pulses of progesterone (P4) (10 min on, 30 min off; 10 ng/ml) during a 240-min period. Two female rabbits were also subjected to perfusion with artificial medium, followed by 6 pulses of cholesterol (10 min on, 30 min off; 10 ng/ml) during a 240-min period. The LHRH concentration in perfusates collected every 10 min was measured by RIA. In the 4 females undergoing 6- to 7-h control push-pull perfusions, spontaneous pulses were observed, with about 1 pulse every 60 min, and a variable amplitude of the LHRH signal, with a mean release of about 0.91 pg/10 min. In the 4 does treated with pulsatile P4 at 10 ng/ml, the mean LHRH release rate increased significantly from 0.91 +/- 0.13 to 1.66 +/- 0.20 pg/10 min (P less than 0.035), primarily due to an increase in the amplitude of the LHRH pulses, which were significantly greater than controls. This response occurred with an apparent mean latency of about 50 min. Cholesterol pulses did not affect the spontaneous activity of the LHRH neural apparatus. In the 4 males undergoing 5- to 9-h control push-pull perfusions, spontaneous LHRH pulses were observed with about 1 pulse every 60 min, and the mean release increased from 1.25 +/- 0.56 to 1.54 +/- 0.55 (P less than 0.035, by Wilcoxon's matched pairs signed rank test) in the late afternoon primarily due to an increase in the amplitude of the pulses. P4 pulses did not affect the spontaneous activity of the LHRH neural apparatus compared to that in the control animals. Overall, these results clearly demonstrate that although spontaneous pulsatile LHRH release from the hypothalamus of awake unrestrained female and male rabbits is similar, pulses of P4 can activate only the female LHRH neural apparatus, with an apparent latency to peak LHRH release of approximately 50 min. In addition, there appears to be an increase in LHRH mean release levels in the late afternoon to early evening in male rabbits.