Gonadotropin-releasing hormone: one polypeptide regulates secretion of luteinizing and follicle-stimulating hormones

Antagonists of luteinizing hormone releasing hormone with novel unnatural amino acids at position six

Five new antagonists of luteinizing hormone releasing hormone (LHRH) containing novel unnatural amino acids at position six are reported. They are very effective in the rat antiovulatory assay. Using saline as vehicle, antagonist-[N-Ac-D-2-Nal1, D-4-Cl-Phe2, D-3-Pal3, Arg5, D-A26, D-Ala10]-LHRH inhibited ovulation completely at 1 micrograms/rat and three of the other antagonists showed some antiovulatory activity at 0.5 micrograms/rat.

Inhibin and related proteins: localization, regulation, and effects

Inhibin has originally been defined as a gonadal hormone that exerts a specific negative feedback action on the secretion of FSH from the gonadotropic cells of the pituitary gland. The existence of inhibin was postulated by Mottram and Cramer (15) as early as 1923. However, only after reliable and sensitive bioassay systems had been developed for detection and estimation of inhibin and an ample source of inhibin was found in the form of ovarian follicular fluid, was progress made on the isolation and characterization of the hormone. It is apparent now that inhibin, which itself consists of a dimer of two different subunits, alpha and beta, is a member of a much larger family of (glyco)protein hormones and growth factors that includes Müllerian inhibiting substance, transforming growth factor-beta, activin/erythroid differentiation factor, bone morphogenetic proteins, and an insect and a Xenopus protein. All play important roles in cell differentiation. Gonadal inhibin is produced in the Sertoli cells in the testis and in the granulosa cells in the ovary. The production of inhibin is stimulated by FSH, but controversy exists about other factors that might play a role in the regulation of the production of inhibin. It appears likely that inhibin plays an important role in the feedback regulation of peripheral concentrations of FSH during the period in which Sertoli cells and granulosa cells--the target cells for FSH--divide, i.e., during puberty in male animals and during the development of ovarian follicles in female animals. In this way, inhibin may be an important regulator of the number of developing Sertoli cells and of the length of the seminiferous tubuli in the testis and of the number of developing follicles in the ovary. Apart from its function in the pituitary-gonadal axis, inhibin and activin may be produced and act in a number of other organs such as the placenta, hypothalamus, adrenal, and bone marrow. Investigation of the role of the members of the inhibin family in these systems has only begun, but will certainly be a field of major interest in the near future.

Luteinizing hormone-releasing hormone (LHRH)-expressing cells do not migrate normally in an inherited hypogonadal (Kallmann) syndrome

Kallmann syndrome inherited hypogonadotropic hypogonadism with anosmia, is associated with an X-chromosome deletion at Xp 22.3. In a Kallmann fetus, we have found an absence of luteinizing hormone-releasing hormone (LHRH)-expressing cells in the brain despite dense clusters of LHRH cells and fibers in the nose. LHRH-containing cells and neurites end in a tangle beneath the forebrain, within the dural layers of the meninges, on the dorsal surface of the cribriform plate of the ethmoid bone. Normal fetal brains, matched for age and sex, had LHRH cells and fibers, as expected, in the hypothalamus and preoptic area. Since LHRH-expressing cells recently were discovered to migrate from the olfactory placode into the brain, it appears that the hypogonadotropism of the Kallmann syndrome can be accounted for by a failure of LHRH cells to migrate into the brain.

Development of a radioimmunoassay for measuring gonadotrophin releasing hormone in patients receiving treatment

A radioimmunoassay for the measurement of gonadotrophin releasing hormone (GnRH) in plasma and urine using readily available reagents was developed. The GnRH assay showed good precision, recovery, and parallelism over a wide range of GnRH concentrations with a sensitivity of 15 pg/ml. The assay was compared with a commercially available kit (Buhlmann Laboratories). Although the Buhlmann kit showed acceptable precision, recovery, sensitivity, and correlation with the developed GnRH assay for plasma samples, lack of parallelism of serially diluted plasma and urine samples was consistently observed, together with a poor correlation with the developed GnRH assay for urine, suggesting a matrix effect with the Buhlmann kit. The developed assay is suitable for measuring GnRH in samples obtained from patients receiving pulsatile infusions of GnRH. In contrast, the commercially available Buhlmann kit was unsuitable for measuring plasma GnRH as the kit had a top standard of only 160 pg/ml, well below the peak plasma concentration. It would not be possible to dilute samples for analysis because of the lack of parallelism of diluted samples compared with standards obtained with the Buhlmann assay.

Effect of luteinizing hormone-releasing hormone on the mechanical activity of the guinea-pig cardiac muscle

1. The inotropic effect of physiological concentrations of luteinizing hormone-releasing hormone (LH-RH) in isolated guinea-pig cardiac muscles was studied. 2. LH-RH increased the contractile force elicited by either fast and slow responses in a dose-dependent manner. 3. These effects of LH-RH were affected by phentolamine and diltiazem but not by propranolol and cold condition. 4. This study showed the positive inotropic effect of LH-RH on myocardium through the affection to intracellular Ca, and the difference from the effect of cardiotonic steroids.

Changes in the endocrine system controlling reproduction in mature female rats neonatally exposed to a low dose of gamma irradiation

Female rats which were exposed to a single low dose of gamma irradiation (6R or 15R) at the age of 8 days produce smaller litters when mature than untreated controls. The possibility that such an impaired reproductive performance could result from changes in the endocrine system was investigated. Plasma levels and hypophyseal contents of LH and FSH, plasma levels of testosterone and hypothalamic content of GnRH were determined. The responsiveness of the pituitary to a single injection of GnRH (50 ng/rat) given on day of proestrus was evaluated. The results indicated that plasma levels of FSH but not of LH were lower in the irradiated rats. This was accompanied by changes in the hypothalamic content of GnRH. The possibility that the pituitary was sensitive to gamma irradiation was excluded. Twenty five minutes after a single injection of GnRH a 2-5 fold increase in LH plasma levels was noticed in all the groups, thus indicating that the reduced fertility could not be attributed to hypophyseal malfunction but rather to an impaired hypothalamic stimulus. Moreover, the lower levels of FSH might result from the significantly elevated levels of testosterone which were observed in the irradiated rats. Apparently, neonatal exposure to a single low dose of gamma irradiation resulted in a new hormonal equilibrium which was responsible for the reduced fertility in such rats.

Secretion of inhibin by chicken granulosa cells in vitro

Inhibin activity was investigated using chicken granulosa cell culture medium. Chicken granulosa cells were collected individually from the largest follicle (F1 follicle) and the third largest follicle (F3 follicle) of the ovary, dispersed using enzyme and incubated in a suspension method or cultured in a monolayer method in vitro. Culture medium was assessed for follicle-stimulating hormone (FSH) inhibiting (inhibin) activity using the rat anterior pituitary cell culture method. The FSH secretion from cultured rat pituitary cells was suppressed by experimental increasing of the amounts of granulosa cell culture medium in a dose-dependent manner, though luteinizing hormone (LH) secretion was not affected in a dose-dependent manner. Inhibin activity of the granulosa cell culture medium derived from F1 follicles was higher than that from F3 follicles. These results suggest that chicken granulosa cells secrete inhibin-like substance(s) and that the F1 follicle may secrete a larger amount of inhibin than the F3 follicle.

Assessment of the effects of a synthetic gonadotropin-releasing hormone associated peptide on hormone release from the in situ and ectopic pituitaries in adult male rats

The in vivo effects of synthetic human gonadotropin-releasing hormone associated peptide (GAP) were evaluated in adult male rats. In normal rats, intracerebroventricular (III ventricle) injection of 5 ng GAP significantly increased plasma LH levels after 60 minutes. Intracerebroventricular administration of 5, 25 or 125 ng of GAP elevated circulating LH levels also at 120 minutes of injection but did not alter plasma FSH, prolactin or testosterone concentrations. In hypophysectomized-pituitary-grafted rats injection of 125 ng GAP directly into the ectopic pituitary induced no changes in peripheral hormone levels. However, intrapituitary graft injection of 25 ng of GnRH significantly elevated circulating levels of LH and testosterone. These results indicate that the ectopic pituitary graft can respond to acute exogenous GnRH stimulation and that the commercially available synthetic GAP fails to inhibit prolactin release in adult male rats.

Dynamic changes in inhibin messenger RNAs in rat ovarian follicles during the reproductive cycle

The alterations in morphology and function of the ovarian follicle as it matures, ovulates, and becomes a corpus luteum are dramatic. A variety of steroid and polypeptide hormones influence these processes, and the ovary in turn produces specific hormonal signals for endocrine regulation. One such signal is inhibin, a heterodimeric protein that suppresses the secretion of follicle-stimulating hormone from pituitary gonadotrophs. Rat inhibin complementary DNA probes have been used to examine the levels and distribution of inhibin alpha-and beta A-subunit messenger RNAs in the ovaries of cycling animals. Striking, dynamic changes have been found in inhibin messenger RNA accumulation during the developmental maturation of the ovarian follicle.

Purification of FSH-releasing factor: its dissimilarity from LHRH of mammalian, avian, and piscian origin

Sheep stalk median eminence fragments were lyophylized, extracted and filtered through a column of Sephadex G-25. The fractions were then assayed for the presence of LHRH by radioimmunoassay (RIA) and bioassayed for FSH and LH-releasing activity following their IV injection into ovariectomized, estrogen progesterone-blocked rats. The radioimmunoassayable LHRH emerged from the column at the same position from which it emerged many years before when LH was measured by bioassay. This same region also contained the LH-releasing activity as measured by bioassay. FSH-releasing activity was present in two tubes just preceding the emergence of the bio- and immunoassayable LHRH. The activity was highly significant and there was no LH-releasing activity in the fractions. They contained much less LHRH as determined by RIA than is sufficient to evoke LH release in this assay. The FSH-releasing activity was recovered in the same fractions in which it was found many years ago with this same assay but with measurement of plasma FSH by bio-rather than immunoassay as employed here. A dose-related release of LH was obtained by injection of LHRH in this assay but there was no significant FSH release even with a dose of 27 ng of LHRH per rat. To determine if one of the LHRHs of lower forms might be FSH-RF, Chicken I and II LHRH and Salmon LHRH were also assayed for FSH- and LH-releasing activity. Each of these peptide possessed LH-releasing activity, albeit much less than that of the mammalian peptide but had no FSH-releasing activity whatsoever.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term suppression of luteinizing hormone, follicle-stimulating hormone and testosterone by daily administration of leuprolide

The chronic effect of long-term injections of leuprolide on the hypothalamic, pituitary and gonadal axes have been studied in men with advanced prostatic cancer. The possibility of transient acute changes in luteinizing hormone, follicle-stimulating hormone and testosterone after each daily injection was studied in 31 patients treated for more than 1 year. No evidence of escape from daily 1.0 mg. doses was noted. No pituitary responsiveness was observed at any time point examined. Thus, daily administration of 1.0 mg. leuprolide acetate subcutaneously produces durable, complete suppression of gonadotropins and testosterone for prolonged periods.

Assessment of the sexual and antler potential of the male white-tailed deer (Odocoileus virginianus) by Gn-RH stimulation test

Twelve mature white-tailed bucks were injected with gonadotropin regulating hormone (Gn-RH, 100 micrograms/deer) during the rut (November) and during the spring (April). In the rut, superior bucks (with actual or potential large body weight, trophy antlers and a high social rank) responded to Gn-RH with a small increase of LH (below 20 micrograms/ml) and a profound rise in testosterone (T) (30-50 ng/ml). The inferior animals exhibited high increase of LH (30-40 ng/ml) but a low rise in T (below 10 ng/ml). FSH levels increased only slightly after Gn-RH and the concentrations were not related to reproductive performance. During the spring, increase in LH levels after Gn-RH administration greatly exceeded the rise of T, but no relationship was found between hormonal levels and the reproductive potential. FSH levels increased remarkably after Gn-RH administration. Gn-RH (administered during the rut) might be used for assessment of the potential for reproductive and antler performance.

Selective modulation of FSH and LH secretion by steroids

Significant divergence between the pattern of FSH and LH secretion has been observed in the ovulatory cycle, after ovariectomy and during puberty. The presence of an FSH-releasing factor, gonadal FSH inhibiting and releasing peptides and changes in the pulsatile pattern of LHRH secretion are among the postulates used to explain the divergent secretion of FSH and LH. Experiments in our laboratory have shown considerable evidence of differential regulation of FSH and LH secretion by steroids in the absence of gonadal regulatory peptides. Natural and synthetic estrogens show significant differences in the suppression of FSH and LH in the ovariectomized rat using a standard uterine response to the estrogen as the end point. In the immature ovariectomized rat treated with a low dose of estradiol that is sufficient for the synthesis of progesterone receptors to ensure progesterone sensitivity, but not large enough to induce estrogen triggered LH surges, progesterone administration resulted in a pattern of LH and FSH secretion similar to that observed on the day of proestrus in the cycling rat. Selective secretion of FSH was induced in the estrogen primed immature rat model by the administration of progesterone metabolite 5 alpha-dihydroporgesterone (5 alpha-DHP) while selective LH secretion was induced by 3 alpha, 5 alpha-tetrahydroprogesterone (3 alpha,5 alpha-THP). The selective secretion of FSH and LH induced by progesterone metabolites was confirmed in the immature female rat primed with PMSG and maintained in constant light. 5 alpha-DHP was also able to induce a greater release of FSH when administered to the adult cycling rat on proestrus. The priming of the pituitary gonadotrope in secreting a high baseline level of FSH or responding to LHRH in releasing a greater amount of FSH appeared to be an important factor in selective FSH release and such priming can be brought about by 5 alpha-DHP in the absence of gonadal regulatory peptides.

A deletion truncating the gonadotropin-releasing hormone gene is responsible for hypogonadism in the hpg mouse

Hereditary hypogonadism in the hypogonadal (hpg) mouse is caused by a deletional mutation of at least 33.5 kilobases encompassing the distal half of the gene for the common biosynthetic precursor of gonadotropin-releasing hormone (GnRH) and GnRH-associated peptide (GAP). The partially deleted gene is transcriptionally active as revealed by in situ hybridization histochemistry of hpg hypothalamic tissue sections, but immunocytochemical analysis failed to show the presence of antigen corresponding to any part of the precursor protein.

Estrogen-dependent effects of norepinephrine on hypothalamic gonadotropin-releasing hormone release in the rabbit

In the rabbit, either coitus or intraventricular administration of norepinephrine (NE) induces gonadotropin release and ovulation. It is hypothesized that ovulation induced with these manipulations involves activation of neuronal pathways that include catecholaminergic and peptidergic neurons. The aim of this study was to examine if perfusion of NE directly through the mediobasal hypothalamus (MBH) stimulates gonadotropin-releasing hormone (GnRH) release from the MBH in ovariectomized (OVEX) and estradiol-treated OVEX does (OVEX/E2). All does were fitted with push-pull (PP) cannulae directed to the MBH and subsequently subjected to PP perfusion at a flow rate of 20 microliters/min for 6 h to measure hypothalamic GnRH release. Five OVEX/E2 and 7 OVEX does received NE that was added to the PP system (intrahypothalamic NE perfusion) at the rate of 2.5 micrograms/min for 2 h during 6 h of PP perfusion. In addition, 6 OVEX/E2 does were given intrahypothalamic perfusion of homovanillic acid (HVA), a metabolite of the adrenergic system, to serve as controls. All PP samples were collected on ice at 10-min intervals, and jugular vein blood samples were obtained at 20-min intervals. The GnRH, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) were measured by specific radioimmunoassays. In OVEX/E2 does, intrahypothalamic perfusion of NE, but not HVA, stimulated a 10-fold increase in peak values of hypothalamic GnRH within 30 min, and a 3-fold increase in peak values of plasma LH within 40 min. Thereafter, both GnRH and LH levels returned to basal values by the end of the NE perfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Peptide-steroid interactions in brain regulation of pulsatile gonadotropin secretion

Reproductive function is regulated by an intricate system of peptide, steroid and amine factors interacting within the brain, pituitary and gonads. At no point is the complexity of the reproductive system better exemplified than in the exquisite interplay of factors required to produce and modulate pulsatile gonadotropin secretion. By extension, analysis of the pulsatile secretory pattern of the gonadotropins, as a means of assessing the contribution of these various factors, can reveal interactions too subtle to be detected by the conventional examination of mean gonadotropin concentration. Analysis of the pulsatile secretory patterns of both LH and FSH reveals striking differences between the two gonadotropins in their response to inhibitory, gonadal peptide and steroid factors, suggesting divergent paths of brain-pituitary regulation. Further studies to clarify this disparity in regulation have demonstrated that neutralization of endogenous LHRH completely abolishes pulsatile LH secretion without affecting pulsatile FSH secretion, suggesting the existence of another, as of yet unknown, brain factor which regulates FSH secretion. The feedback signals provided by gonadal steroids can induce both inhibition and facilitation of LHRH and LH secretion. Neurons of the central opiatergic system exert a tonic inhibitory influence on the catecholaminergic neurons regulating LHRH secretion, and are believed to mediate the inhibitory actions of the gonadal steroids on the LHRH system. Withdrawal of the gonadal steroids has been reported to cause a rapid loss of the tonic inhibitory control of the opiate system on LHRH secretion as revealed by a lack of response to naloxone. Reassessment of this system by analyzing the pulsatile pattern of LH secretion, however, reveals that the loss of naloxone effect after gonadectomy occurs very gradually and that an effect can still be obtained up to 2 weeks after the removal of gonadal steroids. These studies provide excellent examples of the complex interplay observed just between selected factors regulating pulsatile gonadotropin secretion. The use of pulsatile gonadotropin analysis is a powerful model, not only for providing greater clarity of known regulatory interactions, but also for revealing new and more subtle levels of control in the brain-pituitary-axis.

Differences between early- and late-maturing genotypes of the platyfish (Xiphophorus maculatus) in the morphometry of their immunoreactive luteinizing hormone releasing hormone-containing cells: a developmental study

Immunoreactive luteinizing hormone releasing hormone (ir-LHRH) containing perikarya, brain nuclei, and pituitary cells were studied during the postnatal development of male sibling platyfish (Xiphophorus maculatus) genetically determined to reach puberty at two different ages using immunocytochemical, cytological, and morphometric methods. Ir-LHRH-containing perikarya first appear in the nucleus olfactoretinalis (NOR) at 5 weeks of age in early maturers and at 11 weeks in late maturers at a maximum number which is similar in both genotypes and remains constant into adulthood. The dimensions of the NOR and its perikarya increase up to the initiation of sexual maturation (gonopodial stage 2) in both genotypes. In the nucleus preopticus periventricularis (NPP), ir-perikarya appear at stage 2 and are maximum in number at maturity (stage 6) when early maturers have 50% more than late maturers. Measurements for the NPP increase between 1 week and stage 6 in both genotypes. In the nucleus lateralis tuberis (NLT), ir-perikarya appear soon after stage 2 in early maturers but are never seen in late maturers. Late maturers also have fewer ir-LHRH containing pituitary cells than early maturers. In both genotypes, measurements for the NLT increase to stage 2 and then decrease to stage 6. During sexual development there are differences between early- and late-maturing genotypes in the morphometry of their LHRH-containing brain centers. The timing of sexual development creates significant differences in the cytological and cytometric characteristics of the three ir-LHRH-containing brain nuclei in fish of the same age but different genotype. Our results also show that for both genotypes there is a positive correlation between the total number of ir-LHRH brain neurons and the total number of ir-pituitary cells and both are lower for late maturers at every age and stage.

A new hormonal therapy for prostatic cancer: long-term clinical and hormonal response

Twenty-four patients with advanced prostatic cancer were treated with daily injections of the LHRH analogue ICI 118630 (Zoladex) for up to 2 1/2 years. Successful long-term suppression of LH (luteinising hormone) and testosterone was observed without any escape of testosterone. Immunoreactive LH concentrations rose significantly following the daily injection of LHRH analogue but there was no corresponding rise in testosterone concentrations, suggesting altered bioactivity of the LH. A long-term clinical response was obtained in 10 patients (41.6%) and the median duration of response in these patients was 25 months. Eight of the 10 had well to moderately differentiated tumours. The actuarial median survival of all patients was 22 months.

Gonadotropin releasing hormone analogs for female contraception by inhibition of ovulation

One hundred and one healthy regularly ovulating women used two superactive GnRH agonists, Buserelin and Nafarelin, for contraception for 3-26 months. The superagonists were administered once daily by a nasal spray. The treatment was initiated on one of the first 3 days of the menstrual cycle. Seventy-one volunteers used 200, 400 or 600 micrograms of Buserelin for contraception for 3-26 months. Normal ovulation was disturbed in all but 3 of 628 treatment months. No pregnancy occurred. Fifty-three women had regular or sparse menstrual-like bleedings during treatment while 18 developed amenorrhea. Normal ovulation and fertility rapidly returned after cessation of therapy. Thirty women received 125 or 250 micrograms of Nafarelin intranasally once daily for 3 months. The treatment consistently inhibited ovulation without serious side effects. The inhibition of ovulation by prolonged continuous intranasal GnRH agonist therapy is a promising new lead to peptide contraception in women.

A prolactin-inhibiting factor within the precursor for human gonadotropin-releasing hormone

The cloned complementary DNA sequence encoding the human gonadotropin-releasing hormone (GnRH) precursor protein was used to construct an expression vector for the bacterial synthesis of the 56-amino acid GnRH-associated peptide (GAP). GAP was found to be a potent inhibitor of prolactin secretion and to stimulate the release of gonadotropins in rat pituitary cell cultures. Active immunization with peptides corresponding to GAP sequences led to greatly increased prolactin secretion in rabbits.

Immunocytochemistry of luteinizing hormone-releasing hormone during spontaneous and thyroxine-induced metamorphosis of bullfrogs

Double-bridge peroxidase-antiperoxidase immunocytochemistry was used to compare the developmental appearance of immunoreactive LH-RH (ir-LH-RH) in brains of bullfrog (Rana catesbeiana) tadpoles during either spontaneous or thyroxine-induced metamorphosis. During spontaneous metamorphosis, ir-LH-RH was localized in fibers of the external layer of the median eminence (ME) of stage XIII-XXV animals, while immunoreactive perikarya and other immunostained brain structures were absent. The extent and intensity of ME immunostaining increased concomitantly with measured ME morphological development. Tadpoles induced with thyroxine to metamorphic stages XIX-XXI exhibited ME structural development and neurohypophysial neurosecretory staining similar to spontaneously metamorphosed individuals of equal stages. However, comparable ME ir-LH-RH immunostaining and gonadal size were both less developed in thyroxine-treated animals, although increased relative to non-metamorphic vehicle-injected controls. These results indicate that the hypothalamic LH-RH system changes concurrently with ME structural development during spontaneous metamorphosis. Reduced ME ir-LH-RH staining and gonadal size in thyroxine-treated animals suggest that during prometamorphosis, factors other than thyroxine alone may coordinate the normal maturation of the hypothalamo-pituitary-gonadal axis of the bullfrog.

Sexual maturation of the hypothalamus: pathophysiological aspects and clinical implications

Sexual maturation in humans begins early in fetal life and culminates in adulthood when the gonads have acquired a full capacity for reproduction. It is remarkable that during this long process, the pituitary gonadal function, hence its hypothalamic control presents an alternative of activation and inhibition periods, during which the interrelations of the 3 components of the hypothalamic-pituitary-gonadal axis change gradually and inversely. The ontogeny of the hypothalamic-pituitary system, the varying activity of the reproductive endocrine system throughout sexual maturation and the developmental changes in the interrelations of the hypothalamic-pituitary-gonadal axis are reviewed: the most striking feature of human sexual development is the long inhibition of hypothalamo-pituitary function during childhood. Much indirect evidence points to the determining role of the CNS in the maturation of hypothalamic function: the occurrence of rhythms of secretion, the amplitude of secretions and peripubertal specific sleep-related nycthemeral rhythm of secretion at the onset of puberty. Despite the reality of a negative feedback control, these changes do occur independently of gonadal secretions since they are observed (qualitatively if not strictly quantitatively) in agonadal children. It is likely that neurotransmitters (dopamine, serotonine) and opiates have an inhibitory effect on Gn-RH release. But we still don't know their evolution during sexual maturation. It does not appear that melatonine plays any determinant role in the onset of human puberty. The clinical implications of our present understanding of the physiological events occurring during sexual maturation are several. Considering the major problems related to abnormal sexual maturation we will discuss successively: (1) diagnosis of hypogonadotrophic hypogonadism in early infancy; (2) differential diagnosis between premature thelarche and true sexual precocity; (3) the usefulness of endocrine investigations in the evaluation of hypothalamic-pituitary function; and (4) the new developments in the treatment of precocious puberty, delayed puberty or hypogonadism.

Interaction between the posterior pituitary and LHRH in the control of LH secretion

We have recently reported that the posterior lobe of the pituitary differentially inhibits the secretion of prolactin (PRL) and luteinizing hormone (LH), but not follicle stimulating hormone (FSH) throughout the estrous cycle. Removal of the posterior pituitary (posterior pituitary lobectomy) results in elevations of plasma LH on all days of the cycle except on diestrus-day-2. In the present study we examined: whether the control of LH release involves an interaction between the posterior pituitary and hypothalamic luteinizing hormone-releasing hormone (LHRH), and whether the elevation of LH seen following posterior lobectomy is due to the removal of a posterior pituitary substance(s) which alters anterior pituitary sensitivity to LHRH. In order to block the action of hypothalamic LHRH, a potent LHRH inhibitory analog (50 micrograms) was injected SC two hours prior to removal of the posterior pituitary in estrous rats. Administration of the inhibitory analog completely eliminated the elevation of plasma LH seen following posterior lobectomy, but did not alter the posterior lobectomy-induced rise of plasma PRL, or plasma FSH concentrations. In order to test whether anterior pituitary sensitivity to LHRH is altered by posterior lobectomy, a moderate dose of LHRH (15 ng) was administered to both posterior lobectomized and sham lobectomized estrous rats. The time-course and magnitude of the LH response to LHRH was similar in both groups. The results are consistent with the hypothesis that LH secretion is controlled by an interaction between hypothalamic LHRH and the posterior lobe of the pituitary, but this interaction does not appear to involve lobectomy-induced changes in anterior pituitary responsiveness to LHRH.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Long-term stability of aqueous solutions of luteinizing hormone-releasing hormone assessed by an in vitro bioassay and liquid chromatography

The stability of aqueous solutions of luteinizing hormone-releasing hormone (LHRH) after extended storage at various temperatures was investigated using a newly developed HPLC assay and an in vitro dispersed pituitary cell culture bioassay. Good correlations were obtained between the potency obtained by HPLC and bioassay in samples stored at 37 degrees C or subjected to different stress conditions. No significant decrease in activity of LHRH was observed in aqueous solutions stored at 37 degrees C for up to 10 weeks, at 4 degrees C for 2 years, or subjected to repeated freezing and thawing for 5 d. Heating to 60 degrees C in sterile pH 9.0 buffer up to 11 d and storage at ambient temperature in nonsterile solution for 4 months produced well-distinguished degradation products and a decrease in potency. It is concluded that sterile aqueous solutions of LHRH are stable for at least 10 weeks at 37 degrees C and, thus, could be reliably used for chronic administration when long-term stability at body temperature is important.

Mechanism of action of gonadotropin-releasing hormone-stimulated Leydig cell steroidogenesis. I. The stimulatory effect is calcium dependent and not mediated by cyclic nucleotides

The present study was designed to elucidate mechanisms responsible for gonadotropin-releasing hormone (GnRH)-stimulated testosterone formation. Purified Leydig cells from adult Sprague-Dawley rats were incubated with varying concentrations of GnRH agonist (des-Gly10, (D-Ala6) GnRH N-ethylamide), hCG, 8-bromo cAMP or pregnenolone; testosterone, cAMP, cyclic GMP (cGMP) and cAMP-dependent protein kinase activity were measured after various time periods. Basal testosterone levels were 2.54 +/- 0.13 ng/10(5) cells, increasing to 3.18 +/- 0.14, 4.32 +/- 0.08, and 4.63 +/- 0.12 ng within 1 hour after the addition of 10(-9), 10(-8), and 10(-7) M GnRH agonist, respectively. After a 3-hour incubation a 10(-7) M dose of GnRH agonist increased testosterone production four-fold above control. GnRH agonist potentiated hCG-stimulated testosterone formation, but had no significant effects on cGMP levels and cAMP-dependent protein kinase activity. Cyclic AMP levels in the incubation medium increased slightly. GnRH agonist also enhanced 8-bromo-cAMP and pregnenolone-induced testosterone formation. Furthermore, GnRH agonist increased testosterone formation both in the absence and presence of phosphodiesterase inhibitor. These results suggest that the major effect of GnRH agonist is probably beyond the cAMP step. When purified Leydig cells were incubated in a calcium-free medium, the stimulatory effects of GnRH agonist on testosterone formation were completely abolished, but could be restored by the addition of calcium to the incubation medium. GnRH agonist-induced testosterone formation was also blocked by the addition of nifedipine (a calcium channel blocking agent, 0.1 to 10 micrograms/ml). Finally, GnRH antagonist in a concentration of 10 micrograms/ml completely inhibited GnRH agonist-stimulated testosterone formation.

IN CONCLUSION

GnRH agonist stimulated Leydig cell testosterone formation in short-term incubations. The stimulatory effect is calcium dependent and not mediated by cyclic nucleotides.

Effects of luteinizing hormone releasing hormone on gonadotrophins in the hamster

The changes in serum gonadotrophins in male hamsters following one injection of 15 micrograms luteinizing hormone releasing hormone (LHRH) (Group A) were compared with those following the last injection of LHRH in animals receiving an injection approximately every 12 hr for 4 days (Group B) or 12 days (Group C). Peak follicle stimulating hormone (FSH) levels (ng/ml) were 1776 +/- 218 (Group A), 2904 +/- 346 (Group B), and 4336 +/- 449 (Group C). Peak luteinizing hormone (LH) values (ng/ml) were 1352 +/- 80 (Group A), 410 +/- 12 (Group B), and 498 +/- 53 (Group C). Serum FSH:LH ratios, calculated from the concentrations measured 16 hr after the last LHRH injections, were higher in Groups B and C than in Group A. Similar injections of LHRH (100 ng or 15 micrograms/injection) for 6 days elevated the serum FSH:LH ratio in intact males. Five such LHRH injections (100 ng/injection) blunted the rise in serum LH in orchidectomized hamsters. Direct effects of LHRH on gonadotrophin secretory dynamics or altered brain-pituitary-testicular interactions may alter the ratio of FSH to LH in the hamster.

Control of gonadotrophin secretion by steroid hormones in male castrates: site of oestradiol action

Four normal healthy castrated male transsexuals who were not on hormone therapy for at least 4 months volunteered for this study. Each subject received 3 infusions at weekly intervals--the first consisting of LHRH alone, the second of LHRH and oestradiol and the third of oestradiol alone. Venous blood samples were collected at 20-minute intervals 1 hour before the start and during the whole period of infusion. Plasma concentrations of FSH, LH and oestradiol were measured by radio-immunoassay. On an average, 100 micrograms of LHRH enhanced the area under the LH secretion curve by 177% and under the FSH curve by 68%. Oestradiol had a differential effect on the endogenous secretion of LH and FSH, suppressing them by 53% and 18%, respectively. Similarly, the LHRH-stimulated release of LH was significantly inhibited to a greater extent (42%) than that of FSH (23%, P less than 0.05; paired t test). Such an observation and in the light of our acceptance of the single releasing hormone theory, suggests that the differential actions of oestradiol on the secretions of FSH and LH are due to mechanisms residing in the pituitary.

Differential hypothalamic control of FSH secretion: a review

There are many circumstances in which the release of FSH and LH is dissociated; however, many of these are now thought to be brought about by interactions of LH-releasing hormone (LHRH), which stimulates not only LH but also FSH release, and the gonadal peptide, inhibin, which acts at the pituitary to suppress FSH release selectively. There are also many examples which can only be explained by postulating separate hypothalamic control of FSH and LH release. For example, electrochemical stimulation of the medial preoptic area elicited only LH release, whereas stimulation further caudally elicited equivalent LH release but FSH release as well. Points of stimulation particularly in the dorsal anterior hypothalamic area (DAHA) evoked only FSH release. Furthermore, implantation of prostaglandin E2 in various hypothalamic loci in a region extending from the DAHA caudally and ventrally to the caudal median eminence (ME) selectively elicited FSH release. Lesions of the DAHA resulted in a decrease of plasma FSH but not LH in castrated male and female rats and also suppressed the post-castration rise in FSH in males. In ovariectomized estrogen-primed rats with DAHA lesions, injection of progesterone provoked a normal LH surge but a significantly depressed FSH surge. Anterior ME lesions in castrates lowered LH levels more than FSH levels. Extracts of the DAHA evoked greater FSH and LH release in vitro than could be accounted for by the content of LHRH in the extracts, but there was no preferential release of FSH. On the other hand, extracts of the organum vasculosum lamina terminalis (OVLT) evoked dramatically increased FSH release above that which could be accounted for by the content of LHRH. Lastly, posterior ME extracts had more FSH-releasing activity than could be accounted for by their content of LHRH. All these results suggest the existence of an FSH-releasing factor (FSHRF) and lead to the speculation that the cell bodies of FSHRF neurons are located in the DAHA, with axons projecting to the OVLT and to the posterior ME. In other experiments, attempts were made to purify rat and sheep hypothalamic extracts by gel filtration on Sephadex G-25 and to assay the FSH-releasing activity by both bio- and immunoassay. Using this approach, we obtained evidence for the early emergence of a bioactive FSHRF prior to the emergence of LHRH from the column. Although much more work remains to be done, the accumulated evidence strongly supports the concept of a distinct FSHRF.

Alteration in the plasma testosterone: estradiol ratio: an alternative to the inhibin hypothesis

The data suggest that in the absence of the testis: (1) testosterone can maintain both FSH and LH concentrations chronically within the physiological range; (2) that estradiol preferentially suppresses plasma LH concentration, indicating that the androgenic component of testosterone modulates FSH secretion; and (3) that subphysiological testosterone concentrations accompanied by physiological estradiol levels permit FSH to escape to midcastrate levels while maintaining LH concentration at intact levels. An alteration in the testosterone: estradiol ratio can account for a selective FSH elevation when testosterone production is low. The data provide an alternative explanation for the inhibin phenomenon.

Recovery of hypophyseal-testicular function from sex steroid treatment and the pituitary response to castration in male transsexuals

Twenty-one male transsexuals who had been on steroid hormone therapy for at least 1 year volunteered for this investigation. Their hormone profiles after stopping sex steroid hormone treatment for periods ranging from 2 to 70 days were examined. Based on their testosterone levels before the sex-reassignment operation which includes castration, penectomy and the construction of an artificial vagina, two separate groups can be distinguished; those with low (group A) and the other with normal (group B) levels. The gonadotrophins levels in group A and group B were (respectively) significantly (P less than 0.05) lower and higher than corresponding levels in a group of normal males. Castration had caused elevations of FSH and LH in both groups. Although the increment rates were different, both groups attained the same maximum levels of FSH and LH. Within each group, the patterns of FSH and LH responses to castration were similar. However, differences in rates and time of significant elevation of FSH and LH were noted. These observations indicate that there is a delay between the cessation of steroid treatment and the recovery of testicular and hypophyseal functions. Testicular function seems to be altered by steroid treatment since excessive secretions of FSH and LH are needed to produce normal testosterone levels. The secretions of FSH and LH are controlled in some ways by the same mechanisms, while they, in other respects, are controlled by different factors.

The fetal development of the luteinizing hormone-releasing hormone (LHRH) neuronal systems of the guinea pig brain

We have studied the distribution of LHRH-like immunoreactive material in fetal guinea pig brains beginning at day 25 of gestation. Cells and processes were first detected throughout the peripheral, intracranial and central course of the nervus terminalis at 28 (but not 25) days of gestation. The localization of LHRH in this structure preceded its appearance in the hypothalamus and coincided with the initial detection of immunoreactive LH in the pituitary gland. The possible role of the LHRH neuronal network within the nervus terminals in the development of reproductive function is discussed. Comparisons between the brains of littermates of both sexes were made at each age (days 28 through 60 of gestation) to determine possible differences between the sexes in the development of the LHRH neurosecretory systems. No sexually dimorphic features were evident in these systems throughout the prenatal period except at days 40 and 45. At these ages, differences in the number of LHRH neurons in the arcuate nucleus were found between the sexes in some but not all of the brains examined. These differences in LHRH concentrations may reflect the onset of testicular activity as indicated by an increase in serum testosterone levels. Increased serum testosterone concentrations were observed in the male fetuses beginning at 45 days of gestation. However, cell counts made within this nucleus from days 40 through 60 of gestation indicated no comparable sexual dimorphism in the total neuronal population which appeared to be relatively stable throughout this period of brain growth. The number of immunoreactive LHRH neurons visible throughout the brain increased from days 30 through 45 and fewer LHRH cells were seen on days 50 and 60 of gestation, particularly in the arcuate nucleus. The apparent decrease in visible LHRH neurons was concomitant with an increase in number and more extensive distribution of immunoreactive processes throughout the hypothalamus and in certain extrahypothalamic areas of the brain.

Gonadotrophin response to LH-RH in boys with delayed growth and adolescence

Plasma luteinising hormone (LH) and follicle-stimulating hormone (FSH) concentrations were measured before and after intravenous luteinising hormone-releasing hormone (LH-RH) in 33 boys with growth delay. Eighteen were prepubertal and 15 pubertal. Basal LH and FSH levels were low in both groups with mean increments after LH-RH of 3.2 +/- 0.8 U/l (mean +/- SEM) and 2.6 +/- 0.4 U/l respectively in the prepubertal and 7.4 +/- 0.7 U/l and 2.0 +/- 0.3 U/l in the pubertal boys. The LH increment showed a positive correlation with increasing bone age (r = 0.71, P less than 0.001); FSH did not. The LH-RH response thus appeared normal in relation to the stage of maturity.

Effect of inhibitors of catecholamine synthesis on the pituitary response to LH-RH

Cathecolamines have an important role in the regulation of LH secretion. The effect of two selective blocking drugs of cathecolamines synthesis upon pituitary response to LH-RH was studies. Basal levels of serum LH in rats treated with alpha-methyl-p-tyrosine and diethyldithiocarbamate were significantly lower than those of control rats. Diethyldithiocarbamate induced a greater decrease of LH levels than alpha-methyl-p-tyrosine. The rats treated with diethyldithiocarbamate showed an LH increase after LH-RH stimulation that was significantly higher as compared with control group as well as in alpha-methyl-p-tyrosine treated group.

Endocrinology of testicular neoplasms

The hypothalamic-pituitary-testicular axis finely regulates levels of circulating sex steroids--especially testosterone and estradiol--and spermatogenesis. Testosterone, directly as an androgen and as a prehormone for estradiol, regulates LH secretion at both hypothalamic and pituitary levels. Leydig cells, principally under the control of LH, produce testosterone. Sertoli cells, under the control of FSH, and sensitive to intratesticular levels of testosterone, produce estradiol. This locally produced estrogen seems to be necessary for maturation of the germ cells. An abnormality in this sensitive control system, leading to elevations in gonadotrophins or steroid levels, may be etiologically important in both germ cell and nongerm cell neoplasia. Testicular cancers are associated frequently with endocrinologic manifestations, which may be more disabling to the patient than the malignant potential of the tumor, especially with childhood Leydig cell tumors. Estrogen dominance with an elevated estrogen/testosterone ratio can be seen in any testicular neoplasm and may result in gynecomastia. It may be due to a decrease in circulating testosterone or to an increase in estrogens. Virilization is seen frequently in Leydig cell tumors of adolescents. Further elucidation of hormonal interrelationships should lead to better understanding of the genesis of testicular neoplasia and to more effective therapy.