Follicle-stimulating Hormone-releasing Factor Research Articles

The Similarity of FSH-Releasing Factor to Lamprey Gonadotropin-Releasing Hormone III (l-GnRH-III)

To validate further the existence of a specific hypothalamic follicle stimulating hormone releasing factor (FSHRF), stalk-median eminence (SME) fragments from sheep and whole hypothalami from male rats were purified by gel filtration on Sephadex G-25, and the gonadotropin-releasing activity on hemipituitaries of rats incubated in vitro was determined by bioassay and compared with the radioimmunoassayable luteinizing hormone releasing hormone (LHRH) and lamprey gonadotropin releasing hormone (I-GnRH) activities in the fractions. The FSH-releasing fractions eluted in the same sequence of tubes from the Sephadex column found earlier by in vivo bioassay and were clearly separated from the immunoassayable and bioassay-able LHRH. The radioimmunoassay (RIA) for I-GnRH recognized equally I-GnRH-I and -III but had negligible cross-reactivity with LHRH. Fractionation of rat hypothalamic extract by gel filtration on Sephadex G-25 revealed three peaks of I-GnRH determined by RIA, all of which eluted prior to the peak...

Lamprey GnRH-III acts on its putative receptor via nitric oxide to release follicle-stimulating hormone specifically.

Lamprey gonadotropin-releasing hormone-III (l-GnRH-III), the putative follicle-stimulating hormone (FSH)-releasing factor (FSHRF), exerts a preferential FSH-releasing activity in rats both in vitro and in vivo. To test the hypothesis that l-GnRH-III acts on its own receptors to stimulate gonadotropin release, the functional activity of this peptide at mammalian (m) leutinizing hormone (LH)RH receptors transfected to COS cells was tested. l-GnRH-III activated m-LHRH receptors only at a minimal effective concentration (MEC) of 10(-6) M, whereas m-LHRH was active at a MEC of 10(-9) M, at least 1,000 times less than that required for l-GnRH-III. In 4-day monolayer cultured cells, l-GnRH-III was similarly extremely weak in releasing either LH or FSH, and, in fact, it released LH at a lower concentration (10(-7) M) than that required for FSH release (10(-6) M). In this assay, m-LHRH released both FSH and LH significantly at the lowest concentration tested (10(-10) M). On the other hand, l-GnRH-III had a high potency to selectively release FSH and not LH from hemipituitaries of male rats. The results suggest that the cultured cells were devoid of FSHRF receptors, thereby resulting in a pattern of FSH and LH release caused by the LHRH receptor. On the other hand, the putative FSH-releasing factor receptor accounts for the selective FSH release by l-GnRH-III when tested on hemipituitaries. Removal of calcium from the medium plus the addition of EGTA, a calcium chelator, suppressed the release of gonadotropins induced by either l-GnRH-III or LHRH, indicating that calcium is required for the action of either peptide. Previous results showed that sodium nitroprusside, a releaser of nitric oxide (NO), causes the release of both FSH and LH from hemipituitaries incubated in vitro. In the present experiments, a competitive inhibitor of NO synthase, L-NG-monomethyl-L-arginine (300 micro M) blocked the action of l-GnRH-III or partially purified FSHRF. The results indicate that l-GnRH-III and FSHRF act on putative FSHRF receptors by a calcium-dependent NO pathway.

The similarity of FSH-releasing factor to lamprey gonadotropin-releasing hormone III (l-GnRH-III).

To validate further the existence of a specific hypothalamic follicle stimulating hormone releasing factor (FSHRF), stalk-median eminence (SME) fragments from sheep and whole hypothalami from male rats were purified by gel filtration on Sephadex G-25, and the gonadotropin-releasing activity on hemipituitaries of rats incubated in vitro was determined by bioassay and compared with the radioimmunoassayable luteinizing hormone releasing hormone (LHRH) and lamprey gonadotropin releasing hormone (l-GnRH) activities in the fractions. The FSH-releasing fractions eluted in the same sequence of tubes from the Sephadex column found earlier by in vivo bioassay and were clearly separated from the immunoassayable and bioassayable LHRH. The radioimmunoassay (RIA) for l-GnRH recognized equally l-GnRH-I and -III but had negligible cross-reactivity with LHRH. Fractionation of rat hypothalamic extract by gel filtration on Sephadex G-25 revealed three peaks of l-GnRH determined by RIA, all of which eluted prior to the peak of LHRH. Only the second peak had FSH-releasing but not LH-releasing activity. To determine if this FSH-releasing activity was caused by the presence of l-GnRH in the fraction, the pituitaries were incubated with normal rabbit serum or the l-GnRH antiserum (1:1000), and the effect on the FSH- and LH-releasing activity of the FSH-releasing fraction and the LH-releasing activity of LHRH was determined. The antiserum had no effect on basal release of either FSH or LH but eliminated the FSH-releasing activity of the active fraction without altering the LH-releasing activity of LHRH. Since l-GnRH-I has little activity to release FSH or LH, and its activity is nonselective, whereas previous experiments have shown that l-GnRH-III highly selectively releases FSH with a potency equal to that of LHRH to release LH, the results support the hypothesis that the FSH-releasing activity observed in these experiments was caused by l-GnRH-III or a closely related peptide.

Localization of immunoreactive lamprey gonadotropin-releasing hormone in the rat brain☆

A highly specific antiserum against lamprey gonadotropin-releasing hormone (GnRH) was used to localize l-GnRH in areas of the rat brain associated with reproductive function. Immunoreactive l-GnRH-like neurons were observed in the ventromedial preoptic area (POA), the region of the diagonal band of Broca and the organum vasculosum lamina terminalis, with fiber projections to the rostral wall of the third ventricle and the organum vasculosum lamina terminalis. Another population of l-GnRH-like neurons was localized in the dorsomedial and lateral POA, with nerve fibers projecting caudally and ventrally to terminate in the external layer of the median eminence. Other fibers apparently projected caudally and circumventrically to terminate around the cerebral aqueduct in the mid-brain central gray. By using a highly specific antiserum directed against mammalian luteinizing hormone-releasing hormone (m-LHRH), the localization of the LHRH neuronal system was compared to that of the l-GnRH system. There were no LHRH neurons in the dorsomedial or the lateral region of the POA that contained the l-GnRH neurons. As expected, there was a large population of LHRH neurons in the ventromedial POA associated with the diagonal band of Broca and organum vasculosum lamina terminalis. In both of these regions, there were many more LHRH neurons than l-GnRH neurons and the LHRH neurons extended more dorsally and laterally than the l-GnRH neurons. The LHRH neurons seemed to project to the median eminence in the same areas as those that were innervated by the l-GnRH neurons. Absorption studies indicated that l-GnRH cell bodies were eliminated by adding 1 μg of either l-GnRH-I or 1-GnRH-III, but not m-LHRH to the antiserum before use. Fibers were largely eliminated by the addition of 1 μg l-GnRH-III to the antiserum. No chicken GnRH-II neurons or nerve fibers could be visualized by immunostaining. Because the antiserum recognized GnRH-I and GnRH-III equally, we have visualized an l-GnRH system in rat brain. The results are consistent with the presence of either one or both of these peptides within the rat hypothalamus. Because l-GnRH-I has only weak nonselective gonadotropin-releasing activity, whereas l-GnRH-III is a highly selective releaser of follicle-stimulating hormone, and because l-GnRH neurons are located in areas known to control follicle-stimulating hormone release selectively, our results support the hypothesis that l-GnRH-III, or a closely related peptide, may be mammalian follicle-stimulating hormone-releasing factor.

Hypothalamic control of gonadotropin secretion by LHRH, FSHRF, NO, cytokines, and leptin

Gonadotropin secretion by the pituitary gland is under the control of luteinizing hormone-releasing hormone (LHRH) and the putative follicle stimulating hormone-releasing factor (FSHRF). Lamprey III LHRH is a potent FSHRF in the rat and seems to be resident in the FSH controlling area of the rat hypothalamus. It is an analog of mammalian LHRH and may be the long sought FSHRF. Gonadal steroids feedback at hypothalamic and pituitary levels to either inhibit or stimulate the release of LH and FSH, which is also affected by inhibin and activin secreted by the gonads. Important control is exercised by acetylcholine, norepinephrine (NE), dopamine, serotonin, melatonin, and glutamic acid (GA). Furthermore, LH and FSH also act at the hypothalamic level to alter secretion of gonadotropins. More recently, growth factors have been shown to have an important role. Many peptides act to inhibit or increase release of LH and the sign of their action is often reversed by estrogen. A number of cytokines act at the hypothalamic level to suppress acutely the release of LH but not FSH. NE, GA, and oxytocin stimulate LHRH release by activation of neural nitric oxide synthase (nNOS). The pathway is as follows: oxytocin and/ or GA activate NE neurons in the medial basal hypothalamus (MBH) that activate NOergic neurons by alpha 1 (α 1) receptors. The NO released diffuses into LHRH terminals and induces LHRH release by activation of guanylate cyclase (GC) and cyclooxygenase. NO not only controls release of LHRH bound for the pituitary, but also that which induces mating by actions in the brain stem. An exciting recent development has been the discovery of the adipocyte hormone, leptin, a cytokine related to tumor necrosis factor (TNF) α. In the male rat, leptin exhibits a high potency to stimulate FSH and LH release from hemipituitaries incubated in vitro, and increases the release of LHRH from MBH explants. LHRH and leptin release LH by activation of NOS in the gonadotropes. The NO released activates GC that releases cyclic GMP, which induces LH release. Leptin induces LH release in conscious, ovariectomized estrogen-primed female rats, presumably by stimulating LHRH release. At the effective dose of estrogen to activate LH release, FSH release is inhibited. Leptin may play an important role in induction of puberty and control of LHRH release in the adult as well.

Electrochemical stimulation of the median eminence evokes FSH but not LH release after LHRH antagonist treatment in vivo and in vitro.

Experimental data suggest that a follicle stimulating hormone-releasing factor (FSH-RF) distinct from luteinizing hormone-releasing hormone (LHRH) exists. In the present study, we investigated, in short-term ovariectomized (OVX) rats, whether FSH-RF(s) can be released from nerve terminals by electrochemical stimulation (ECS) of the median eminence. To prevent the effect of LHRH liberated by ECS, 100 microg of a potent LHRH antagonist (MI-1544) was administered to one group of OVX rats 60 min before ECS. Two groups of OVX rats were used as controls. One group was treated with the solvent of the LHRH antagonist 60 min before the ECS; the other group received sham-ECS only. In-vitro experiments using a hypothalamus-pituitary coperifusion system were also performed to investigate the direct effect of ECS of the median eminence on LH and FSH release from pituitary cells. ECS in vivo induced 4.6-fold (P<0.01) and 10.2-fold (P<0.01) elevation of serum LH concentration, measured by RIA at 10 min and 60 min after ECS, respectively. Serum FSH concentrations increased 1.35-fold at 10 min (P<0.01) and 1.50-fold at 60 min (P<0.01) after ECS, compared with sham-stimulated controls. Administration of LHRH antagonist attenuated the ECS-induced release of LH by 44% at 10 min and prevented it entirely at 60 min after ECS. However, the ECS-induced release of FSH was not modified by the antagonist at 10 min and was diminished by only 17% at 60 min after ECS, compared with solvent-treated and stimulated controls. Immunohistological examination of the hypothalami showed that LHRH-immunoreactivity was depleted in the region of ECS. In the study in vitro, substances released from the fragments of mediobasal hypothalami bearing ECS in the median eminence induced significant release of both LH and FSH, and the induced release of LH, but not FSH, was prevented by the LHRH antagonist. The present study suggests that FSH-releasing factor(s) different from LHRH can be released from the median eminence and that a significant portion of FSH secretion is independent of the control of LHRH.

The nitric oxide hypothesis of brain aging.

Nitric oxide synthase (NOS)-containing neurons are found in many loci throughout the central nervous system, which include the cerebral cortex, the cerebellum, the hippocampus, and the hypothalamus. NO plays a very important role in control of neuronal activity in all of these areas by diffusing into neurons where it activates soluble guanylate cyclase (sGC) leading to generation of cyclic guanosine monophosphate (cGMP) and cyclooxygenase 1 leading to generation of prostaglandins. Both of these active agents are involved in mediating the actions of NO, the first gaseous transmitter. In the cerebellum, NO is extremely important and it is also thought to mediate long-term potentiation in the hippocampus. Various stresses and corticoids have been shown in monkeys and also in rodents to cause neuronal cell death. This may be via the stimulation of glutamic acid release, which by N-methyl-D-aspartate (NMDA) receptors causes release of NO, which can lead to neuronal cell death. In the hypothalamus,. NO stimulates corticotropin-releasing hormone (CRH), prolactin releasing factor, growth hormone-releasing hormone (GHRH), and somatostatin, lutenizing hormone-releasing hormone (LHRH), but not follicle stimulating hormone-releasing factor (FSHRF) release. In situations of increased release of NO in the hypothalamus, it could cause neuronal cell death. Following bacterial or viral infections, toxic products of the ineffective agents, such as bacterial lipopolysaccharide (LPS), circulate to the brain, where they induce interleukin-1 and iNOS mRNA and synthesis. After several hours delay, massive quantities of NO are released. Induction of iNOS occurs in the choroid plexus, meninges, in circumventricular organs, and in large numbers of iNOS neurons in the arcuate and paraventricular nuclei. The large amounts of NO released by iNOS may well produce death not only of neurons but also glial. Repeated bouts of systemic infection even without direct neural involvement could result in induction of iNOS in the central nervous system and lead to large fall out of neurons in hippocampus to impair memory, hypothalamus to decrease fever, and neuroendocrine response to infection, and could play a role in the pathogenesis of degenerative neuronal diseases of aging, such as Alzheimers. The largest induction of iNOS occurs in the anterior pituitary and pineal glands. The damage to the pituitary could also impair responses to stress and infection, and the release of NO during infection could be responsible for the degenerative changes in the pineal and diminished release of melatonin, an antioxident, and consequently, an antiaging hormone, that occur with age.

Effects of delta-9-tetrahydrocannabinol on the hypothalamic-pituitary control of luteinizing hormone and follicle-stimulating hormone secretion in adult male rats.

The main psychoactive component of marihuana, delta-9-tetrahydrocannabinol (THC) was injected into the 3rd cerebral ventricle. A single dose of THC (2 microliter of 10(-6) M) decreased serum LH temporarily but did not alter serum follicle-stimulating hormone (FSH) levels. The mediobasal hypothalamic (MBH) luteinizing hormone-releasing hormone (LHRH) content was elevated by 30 min after the injection. The elevation persisted for 1 h. Then, the LHRH content returned towards the preinjection level. In contrast, the LHRH in the organum vasculosum of the lamina terminalis did not change after a single dose of THC. The results indicate that THC alters pituitary LH release by inhibiting the release of LHRH which then increases in the MBH by continued synthesis or transport from rostral areas. In addition, the data support the existence of an FSH releasing factor, the release of which is not suppressed by this dose of THC. THC did not alter the release, storage or responsiveness to LHRH of cultured anterior pituitary cells, which further supports the view that its principal site of action is on the hypothalamus.

Role of neurotransmitters and neuropeptides in the control of gonadotropin release: A review

Rapid progress has been recorded recently in the understanding of the role of neuro-transmitters and neuropeptides in the control of reproduction and on their apparent potential in the regulation of fertility. Peptides, as well as monoamines, are important in the control of lutinizing hormone releasing hormone and gonadotropin release. The input from brainstem noradrenergic neurons as well as dopamine mediated stimulated release of lutinizing hormone. In addition considerable evidence exist for the occurrence of a specific follicle stimulating hormone-releasing factor. A large number of brain peptides affect the secretion of lutinizing hormone releasing hormone and the endogenous opioid peptides appear to have a physiologically important function in restraining the influence on lutinizing hormone releasing hormone release under most circumstances. Vasoactive intestinal peptide and substanceP stimulate whereas cholecystokinin, neurotensin, gastrin, secretin, somatostatin α-melanosite stimulating hormone and vasotocin inhibit lutinizing hormone release. Of the inhibitory peptides, cholecystokinin and arg-vasotocin are the most potent. Inhibin injected into the ventricle selectively suppresses follicle stimulating hormone release by a hypothalamic action. Thus the control of gonadotropin release is complex and a number of aminergic and peptidergic transmitters are involved.

The effects of single-dose luteinizing hormone-releasing hormone on ovulatory menstrual function: support for a single luteinizing hormone- and follicle-stimulating hormone-releasing factor

Ten ovulatory women were followed with gonadotropin and steroid determinations through two cycles. They were given 500 micrograms of luteinizing hormone-releasing hormone (LH-RH) during the periovulatory period of the second cycle to determine whether ovulation could be facilitated without altering corpus luteum function. Successive cycles demonstrated concordance for patterns of gonadotropin and steroid secretion when studied as group means. Two control cycles and one treatment cycle were consistent with luteal phase defects. The use of a supramaximal dose of LH-RH in these women neither facilitated ovulation nor adversely affected luteal function. A significant linear correlation was noted between peak LH and follicle-stimulating hormone (FSH) values for the spontaneous surges. This same linear relationship was maintained for the LH and FSH responses to 500 micrograms LH-RH. The present data produce further evidence demonstrating that the secretion of LH and FSH appears to be modulated by gonadal steroids and under the permissive control of a single gonadotropin-releasing hormone.

Generation of Hypophysiotropic Activity in Hypothalamic ExtractsIn vitro

The luteinizing hormone (LH) and follicle stimulating hormone (FSH) releasing activity, as well as the prolactin (PRL) release-inhibiting activity were measured in both neutral aqueous, and acid ethanolic extracts of rat hypothalami. LH and FSH-releasing activities were detectable only in the latter type of extract, whereas PRL release-inhibiting activity appeared in both. Neutral ultrafiltrates of the neutral extracts contained no gonadotropin releasing activity, however, acidification of the filtration medium induced its appearance. PRL release was inhibited by both neutral and acid filtrates. These results suggest that LH and FSH releasing factor(s) may be stored in the hypothalamus in an inactive form from which the active peptide is generated in vitro under acid conditions; however, this does not appear to be true for the component(s) responsible for the inhibition of PRL release.

Acetylcholine and the release of the follicle-stimulating hormone-releasing factor.

The possible participation of cholinergic inputs in the release of FSH-RF has been studied using an in vitro approach. Halved anterior pituitaries (AP) of normal adult male rats have been incubated for 4 hr either alone or in the presence of hypothalamic fragments (HF). Atthe end of the incubation period FSH has been evaluated using a biological assay both in the media and in the AP tissue. AP halves, when incubated alone, release a small amount of FSH. The addition of HF to the media containing AP tissue brings about a significant increase of the amounts of FSH released. A.cetylcholine (Ach) added to the incubation flasks containing only AP tissue does not increase FSH output over that of AP incubated without Ach. On the contrary, Ach significantly enhances FSH release when added to the incubation media of flasks containing both AP tissue and HF. Atropine, an anticholinergic drug, has no effect on the release of FSH from APincubated alone. Atropine totally prevents the release of FSH normally induced by ...

Localization of Neuroendocrine Functions Within the Hypothalamus

SUMMARYThe results of lesion, stimulation, deafferentation, implantatión and transplantation studies employed in the identification of hypophysiotrophic control areas in the hypothalamus to date suggest the following probable locations: corticotropic releasing factor (CRF) is formed in a diffuse area along the base of the median eminence, if not the base of the entire hypothalamus. Follicle stimulating hormone releasing factor (FSHRF) is elaborated in the paraventricular-suprachiasmatic areas but its cyclic control may reside in the anterior hypothalamic area. Luteinizing hormone (LH) is controlled by luteinizing hormone releasing factor (LHRF) formed in the suprachiasmatic area: its cyclic control may be in the preoptic area. Prolactin is controlled by prolactin inhibiting factor (PIF) localized in a diffuse area comprising the ventromedial, dorsomedial, arcuate and paraventricular nuclei. The hypothalamic area involved in thyroid control is also rather large, since thyrotropin stimulating hormone releasing factor (TSHRF) has been found in an area including the supraoptic and chiasmatic nuclei. Growth hormone releasing factor (GHRF) is elaborated in a rather narrow zone, the ventromedial hypothalamic nuclei.

Involvement of brain catecholamines in the gonadotropins-releasing mechanism(s) before puberty.

The involvement of brain catecholamines (CA) in the neuroendocrine mechanism(s) that controls the secretion of pituitary gonadotropins has been clearly established in adult, but not in immature, rats. Daily administration of an inhibitor of CA synthesis, a-methyltyrosine (a- MT, ISO mg/kg ip) to 20-day-old hemiovariectomized (Hm Ovx) rats, completely suppressed the ovarian compensatory hypertrophy (OCH) present 4 days after operation. Combined treatment with β-MT and 1-3,4-dihydroxyphenylalanine (L-DOPA, 100 mg/kg ip), a precursor of brain noradrenaline (NA) and dopamine (DA), prevented the blocking effect of β-MT on OCH. The effect of a-MT was also abolished by DL-threo- 3,4-dihydroxyphenylserine (DOPS, 200 mg/kg ip), a drug which selectively restores brain NA levels. DL-p-Chlorophenylalanine (PCPA, 250 mg/kg ip), an inhibitor of serotonin (S-HT) synthesis, did not modify OCH. Pituitary FSH content was unaltered in hemiovariectomized rats treated with saline, β-MT or β-MT plus L-DOPA on comparison with values present in intact controls. Hypothalamic follicle stimulating hormone releasing factor (FSH-RF) disappeared completely in Hm Ovx controls; administration of β-MT to Hm Ovx rats resulted in the reappearance of FSH-RF in the hypothalamus, which was still present after combined treatment with β-MT plus L-DOPA. Biochemical determinations of NA, DA and S-HT provided evidence on the effects of the drugs used on actual brain monoamine levels. It is concluded that brain CA, namely NA, play a role in the regulation of FSH secretion before puberty; their underlying mechanism(s) of action is discussed. (Endocrinology90: 1267, 1972)

Development of neural regulation of follicle stimulating hormone (FSH) secretion.

Hypothalamic follicle stimulating hormone releasing factor (FSHRF) content, pituitary and plasma follicle stimulating hormone (FSH) concentrations have been determined in female rats between 5 and 75

CENTRAL NERVOUS INFLUENCES ON GONADAL FUNCTIONS

Experiments involving electrolytic lesions of hypothalamic nuclei, localized implantations of blockers of protein synthesis and the »deafferentation« of the basal hypothalamus have shown that, in the rat, the Follicle Stimulating Hormone-Releasing Factor (FSH-RF) is synthesized in the paraventricular region; the same techniques have indicated that the Luteinizing Hormone-Releasing Factor (LH-RF) is manufactured in two different areas, i. e. the suprachiasmatic and the arcuate-ventromedial ones.

Requirement of Ca++ and Mg++ ions for the in vitro release of follicle-stimulating hormone from rat pituitary glands and in its subsequent biosynthesis.

The in vitro release of FSH from rat pituitary glands, when stimulated by a specific releasing factor, viz., follicle-stimulating hormone releasing factor (FRF), or nonspecific factors such as cyclic 3′,5′-AMP (cAMP), or high [K+] medium, required the presence of Ca++ in the external medium. Ca++ together with cAMP probably plays an active intracellular role in the processes leading to the release of FSH. No definite conclusion can be made as to the requirement for Mg++ in these processes. The synthesis (or activation) of FSH, observed during incubation in the presence of FRF, was also Ca++ dependent. However, further experiments are necessary in order to find out whether the presence of Ca++ is required directly for the synthesis of FSH, or whether the synthesis is only a secondary phenomenon arising from the release of FSH. In the latter case, the lack of Ca++, which inhibited the release of FSH, would consequently inhibit its synthesis. (Endocrinology 86: 761, 1970)

In Vitro Demonstration of Follicle-Stimulating Hormone Releasing Activity in the Chicken Hypothalamus

ALTHOUGH the existence of a follicle-stimulating hormone-releasing factor in the hypothalamus of mammals has been well established (Igarashi and McCann, 1964; Mittler and Meites, 1964; Kuroshima et al., 1965; Schally et al., 1967), evidence of its existence in chickens has not been reported. The present experiments were carried out to demonstrate the follicle-stimulating hormone (FSH)-releasing activity of the chicken hypothalamus on isolated chicken and rat pituitaries in vitro.Fragments of hypothalamic tissues including the pituitary stalk-median eminence were collected from White Leghorn cocks and hens of 1–2 years of age. The tissues, homogenized in 0.1 N HCl solution, were centrifuged and the supernate was immersed in boiling water for 10 minutes to inactivate FSH (Igarashi and McCann, 1964) which might have contaminated the extracts. Cerebral cortical extracts were also prepared in the same way and served as controls. The extracts were neutralized with 1 N NaOH solution just prior…

Possible interaction of luteinizing hormone-releasing factor with other hypothalamic releasing factors at the level of the adenohypophysis.

SUMMARY Anterior pituitary halves from adult male rats were incubated in vitro for 6 hr. in tissue culture Medium 199. Luteinizing hormone (LH) released from these glands under the influence of purified preparations of growth hormone-releasing factor (GH-RF), growth hormone-inhibiting factor (GH-IF), corticotrophin-releasing factor (C-RF) and follicle-stimulating hormone-releasing factor (FSH-RF) was determined by the ovarian ascorbic acid depletion (OAAD) assay. The effects of these factors, both alone and together with purified luteinizing hormone-releasing factor (LH-RF), were examined and compared with the response to purified LH-RF alone. While LH-RF consistently produced significant increases in LH release, none of the other factors did so, although FSH-RF showed some indication of LH-releasing activity, probably due to incomplete separation from LH-RF on the Sephadex gel filtration column used for purification. The LH released in response to LH-RF was not affected by the presence of any of the other factors. An apparent slight augmenting effect of FSH-RF could be accounted for by its contamination with LH-RF. The results are discussed in relation to the physiological mechanisms concerned in modifying LH release from the adenohypophysis.

Induction of ovulation in sheep by intra-adenohypophysial infusion of hypothalamic extracts.

SUMMARY The follicle-stimulating hormone releasing factor (FSH-RF) and luteinizing hormone-releasing factor (LH-RF) activity in sheep hypothalamic extracts and their action on the release of gonadotrophins from the pituitary gland has been studied by the infusion of extracts of the stalk and median eminence (SME) directly into the adenohypophysis of ewes in various phases of their non-cycling quiescent sexual period. The intra-adenohypophysial infusion of hypothalamic extracts during mid-anoestrus elicited no ovarian response, while similar infusion of the same extracts in the late phase of anoestrus, e.g. in the last 2–4 weeks before the onset of the breeding season, induced the growth and rupture of ovarian follicles as well as development of corpora lutea. This ovulatory response provides indirect but strong evidence for the ability of hypothalamic extracts to release gonadotrophins (FSH as well as LH) from the pituitary gland. The seasonal differences in the response of ewes to intra-adenohypophysial infusions of hypothalamic extracts suggest that the sensitivity of the adenohypophysis to the hypothalamic releasing factors varies during the year.