Hypothalamic Luteinizing Hormone-releasing Hormone Release Research Articles

Alcohol alters insulin-like growth factor-1-induced transforming growth factor β1 synthesis in the medial basal hypothalamus of the prepubertal female rat.

Insulin-like growth factor-1 (IGF-1) and transforming growth factor β1 (TGFβ1) are produced in hypothalamic astrocytes and facilitate luteinizing hormone-releasing hormone (LHRH) secretion. IGF-1 stimulates release by acting directly on the LHRH nerve terminals and both peptides act indirectly through specific plastic changes on glial/tanycyte processes that further support LHRH secretion. Because the relationship between these growth factors in the hypothalamus is not known, we assessed the ability of IGF-1 to induce TGFβ1 synthesis and release and the actions of alcohol (ALC) on this mechanism prior to the onset of puberty. Hypothalamic astrocytes were exposed to medium only, medium plus IGF-1 (200ng/ml), or medium plus IGF-1 with 50mM ALC. After 18hours, media were collected and assayed for TGFβ1. For the in vivo experiment, prepubertal female rats were administered either ALC (3g/kg) or water via gastric gavage at 07:30hours and at 11:30hours. At 09:00hours, saline or IGF-1 was administered into the third ventricle. Rats were killed at 15:00hours and the medial basal hypothalamus (MBH) was collected for assessment of TGFβ1, IGF-1 receptor (IGF-1R), and Akt. IGF-1 induced TGFβ1 release (p<0.01) from hypothalamic astrocytes in culture, an action blocked by ALC. In vivo, IGF-1 administration caused an increase in TGFβ1 protein compared with controls (p<0.05), an action blocked by ALC as well as a phosphatidylinositol 3 kinase/Akt inhibitor. IGF-1 stimulation also increased both total (p<0.01) and phosphorylated (p)-IGF-1R (p<0.05) protein levels, and phosphorylated (p)-Akt levels (p<0.01), which were also blocked by ALC. This study shows that ALC blocks IGF-1 actions to stimulate synthesis and release of hypothalamic TGFβ1, total and p-IGF-1R, and p-Akt levels further demonstrating the inhibitory actions of ALC on puberty-related events associated with hypothalamic LHRH release.

Bi-directional associations between galanin and luteinizing hormone-releasing hormone neuronal systems in the human diencephalon

Evidence suggests that galanin plays an important role in the regulation of reproduction in the rat. Galanin is colocalized with luteinizing hormone (LH)–releasing hormone (LHRH) in a subset of LHRH neurons in female rats and galanin-immunoreactive (galanin-IR) nerve terminals innervate LHRH neurons. Recent studies indicate that galanin may control gonadal functions in rats at two different levels: (i) via direct modulation of pituitary LH secretion and/or (ii) indirectly via the regulation of the hypothalamic LHRH release. However, the morphological substrate of any similar modulation is not known in human. In the present series of experiments we first mapped the galanin-IR and LHRH-IR neural elements in human brain, utilizing single label immunohistochemistry. Then, following the superimposition of the maps of these systems, the overlapping sites were identified with double labeling immunocytochemistry and examined in order to verify the putative juxtapositions between galanin-IR and LHRH-IR structures. LHRH and galanin immunoreactivity were detected mainly in the medial basal hypothalamus, in the medial preoptic area and along the diagonal band of Broca. Careful examination of the IR elements in the overlapping areas revealed close, bi-directional contacts between galanin-IR and LHRH-IR structures, which have been verified in semithin plastic sections. These galanin-LHRH and LHRH-galanin juxtapositions were most numerous in the medial preoptic area and in the infundibulum/median eminence of the human diencephalon. In conclusion, the present study is the first to reveal bi-directional juxtapositions between galanin- and LHRH-IR neural elements in the human diencephalon. These galanin–LHRH and LHRH–galanin contacts may be functional synapses, and they may be the morphological substrate of the galanin-controlled gonadal functions in humans.

NEUROENDOCRINE PERTURBATIONS IN FIBROMYALGIA AND CHRONIC FATIGUE SYNDROME

A large body of data from a number of different laboratories worldwide has demonstrated a general tendency for reduced adrenocortical responsiveness in CFS. It is still not clear if this is secondary to CNS abnormalities leading to decreased activity of CRH- or AVP-producing hypothalamic neurons. Primary hypofunction of the CRH neurons has been described on the basis of genetic and environmental influences. Other pathways could secondarily influence HPA axis activity, however. For example, serotonergic and noradrenergic input acts to stimulate HPA axis activity. Deficient serotonergic activity in CFS has been suggested by some of the studies as reviewed here. In addition, hypofunction of sympathetic nervous system function has been described and could contribute to abnormalities of central components of the HPA axis. One could interpret the clinical trial of glucocorticoid replacement in patients with CFS as confirmation of adrenal insufficiency if one were convinced of a positive therapeutic effect. If patient symptoms were related to impaired activation of central components of the axis, replacing glucocorticoids would merely exacerbate symptoms caused by enhanced negative feedback. Further study of specific components of the HPA axis should ultimately clarify the reproducible abnormalities associated with a clinical picture of CFS. In contrast to CFS, the results of the different hormonal axes in FMS support the assumption that the distortion of the hormonal pattern observed can be attributed to hyperactivity of CRH neurons. This hyperactivity may be driven and sustained by stress exerted by chronic pain originating in the musculoskeletal system or by an alteration of the CNS mechanism of nociception. The elevated activity of CRH neurons also seems to cause alteration of the set point of other hormonal axes. In addition to its control of the adrenal hormones, CRH stimulates somatostatin secretion at the hypothalamic level, which, in turn, causes inhibition of growth hormone and thyroid-stimulating hormone at the pituitary level. The suppression of gonadal function may also be attributed to elevated CRH because of its ability to inhibit hypothalamic luteinizing hormone-releasing hormone release; however, a remote effect on the ovary by the inhibition of follicle-stimulating hormone-stimulated estrogen production must also be considered. Serotonin (5-HT) precursors such as tryptophan (5-HTP), drugs that release 5-HT, or drugs that act directly on 5-HT receptors stimulate the HPA axis, indicating a stimulatory effect of serotonergic input on HPA axis function. Hyperfunction of the HPA axis could also reflect an elevated serotonergic tonus in the CNS of FMS patients. The authors conclude that the observed pattern of hormonal deviations in patients with FMS is a CNS adjustment to chronic pain and stress, constitutes a specific entity of FMS, and is primarily evoked by activated CRH neurons.

Secretory pattern of GH, TSH, thyroid hormones, ACTH, cortisol, FSH, and LH in patients with fibromyalgia syndrome following systemic injection of the relevant hypothalamic-releasing hormones.

To study the hormonal perturbations in FMS patients we injected sixteen FMS patients and seventeen controls a cocktail of the hypothalamic releasing hormones: Corticotropin-releasing hormone (CRH), Thyrotropin-releasing hormone (TRH), Growth hormone-releasing hormone (GHRH), and Luteinizing hormone-releasing hormone (LHRH) and observed the hormonal secretion pattern of the pituitary together with the hormones of the peripheral endocrine glands. We found in FMS patients elevated basal values of ACTH and cortisol, lowered basal values of insulin-like growth factor I (IGF-I) and of triiodothyronine (T3), elevated basal values of follicle-stimulating hormone (FSH) and lowered basal values of estrogen. Following injection of the four releasing-hormones, we found in FMS patients an augmented response of ACTH, a blunted response of TSH, while the prolactin response was exaggerated. The effects of LHRH stimulation were investigated in six FMS patients and six controls and disclosed a significantly blunted response of LH in FMS. We explain the deviations of hormonal secretion in FMS patients as being caused by chronic stress, which, after being perceived and processed by the central nervous system (CNS), activates hypothalamic CRH neurons. CRH, on the one hand, activates the pituitary-adrenal axis, but also stimulates at the hypothalamic level somatostatin secretion which, in turn, causes inhibition of GH and TSH at the pituitary level. The suppression of gonadal function may also be attributed to elevated CRH by its ability to inhibit hypothalamic LHRH release, although it could act also directly on the ovary by inhibiting FSH-stimulated estrogen production. We conclude that the observed pattern of hormonal deviations in FMS patients is a CNS adjustment to chronic pain and stress, constitutes a specific entity of FMS, and is primarily evoked by activated CRH neurons.

The anti-gonadotropic effects of cytokines: the role of neuropeptides

The inhibitory effect of inflammation and endotoxins on the secretion of reproductive hormones from the hypothalamo-pituitary axis is well documented. A comparison of the luteinizing hormone (LH) suppressing effects of several pro-inflammatory cytokines revealed that centrally administered IL-1β was the most potent inhibitor of pituitary LH secretion; interleukin (IL)-1α and tumor necrosis factor (TNF)α were relatively less effective, whereas IL-6 was ineffective. This order of potency suggested that the anti-gonadotropic effects of an immune challenge are most likely attributable to the action of centrally released IL-1β, and this was supported by the demonstration that IL-1β suppressed hypothalamic luteinizing hormone releasing hormone (LHRH) release. We used a multifaceted approach to identify the afferent signals in the brain that convey immune messages to hypothalamic LHRH neurons. Pharmacological studies with specific antagonists of opioid receptor subtypes demonstrated that activation of the μ1 receptor subtype was required to transmit the cytokine signal. Furthermore, icv IL-1β upregulated hypothalamic POMC mRNA and increased the concentration and release of β-endorphin, the primary ligand of μ1 receptors. We have obtained evidence that IL-1β also enhanced the gene expression and concentration of tachykinins, a family of nociceptive neuropeptides in the hypothalamus. Blockade of tachykinergic NK2 receptors attenuated IL-1β induced inhibition of LH secretion. Collectively, these results demonstrate that IL-1β, generated centrally in response to inflammation, upregulates the opioid and tachykinin peptides in the hypothalamus. These two groups of neuropeptides are critically involved in relaying the cytokine signal to neuroendocrine neurons and causing the suppression of hypothalamic LHRH and pituitary LH release.

Agmatine, a novel hypothalamic amine, stimulates pituitary luteinizing hormone release in vivo and hypothalamic luteinizing hormone-releasing hormone release in vitro

Agmatine, a clonidine displacing substance and imidazoline receptor agonist, was recently isolated from bovine brain and shown to be present in the rat hypothalamus. Since clonidine can stimulate the release of pituitary luteinizing hormone (LH), we tested the hypothesis that agmatine may similarly act in the rat to stimulate the hypothalamic luteinizing hormone-releasing hormone (LHRH)-pituitary LH axis. Administration of agmatine intracerebroventricularly rapidly augmented the release of LH in a dose-related fashion in ovariectomized, ovarian steroid-primed rats. Additionally, agmatine enhanced the in vitro efflux of LH releasing hormone from the median eminence-arcuate nucleus of the hypothalami of rats similarly pretreated with steroids. These studies imply that the endogenous imidazoline receptor agonist, agmatine, may serve as an excitatory neurotransmitter/neuromodulator in the hypothalamic control of LH release and we suggest that the previously reported excitatory effects of clonidine on LH release may be attributed to stimulation by clonidine of imidazoline receptors.

Nitric oxide inhibits hypothalamic luteinizing hormone-releasing hormone release by releasing gamma-aminobutyric acid.

Nitric oxide synthase (NOS)-containing neurons, termed NOergic neurons, occur in various regions of the hypothalamus, including the median eminence-arcuate region, which plays an important role in controlling the release of luteinzing hormone-releasing hormone (LHRH). We examined the effect of NO on release of gamma-aminobutyric acid (GABA) from medial basal hypothalamic (MBH) explants incubated in vitro. Sodium nitroprusside (NP) (300 microM), a spontaneous releaser of NO, doubled the release of GABA. This release was significantly reduced by incubation of the tissue with hemoglobin, a scavenger of NO, whereas hemoglobin alone had no effect on the basal release of GABA. Elevation of the potassium concentration (40 mM) in the medium increased GABA release 15-fold; this release was further augmented by NP. Hemoglobin blocked the increase in GABA release induced by NP but had no effect on potassium-induced release, suggesting that the latter is not related to NO. As in the case of hemoglobin, NG-monomethyl-L-arginine (NMMA), a competitive inhibitor of NOS, had no effect on basal release of GABA, which indicates again that NO is not significant to basal GABA release. However, NMMA markedly inhibited the release of GABA induced by high potassium, which indicates that NO plays a role in potassium-induced release of GABA. In conditions in which the release of GABA was substantially augmented, there was a reduction in GABA tissue stores as well, suggesting that synthesis of GABA in these conditions did not keep up with release of the amine. Although NO released GABA, there was no effect of the released GABA on NO production, for incubation of MBH explants with GABA had no effect on NO release as measured by [14C]citrulline production. To determine whether GABA had any effect on the release of LHRH from these MBH explants, GABA was incubated with the tissue and the effect on LHRH release was determined. GABA (10(-5) or 10(-6) M) induced a 70% decrease in the release of LHRH, indicating that in the male rat GABA inhibits the release of this hypothalamic peptide. This inhibition in LHRH release induced by GABA was blocked by NMMA (300 microM), which indicates that GABA converts the stimulatory effect of NO on LHRH release into an inhibitory one, presumably via GABA receptors, which activate chloride channels that hyperpolarize the cell. Previous results have indicated that norepinephrine stimulates release of NO from the NOergic neurons, which then stimulates the release of LHRH. The current results indicate that the NO released also induces release of GABA, which then inhibits further LHRH release. Thus, in vivo the norepinephrinergic-driven pulses of LHRH release may be terminated by GABA released from GABAergic neurons via NO.

CRF Alters the Infundibular LHRH Secretory System from the Medial Preoptic Area of Female Rats: Possible Involvement of Opioid Receptors

Corticotropin-releasing factor (CRF) is a potent factor involved in the antireproductive effects of various stressors. However, the central mechanisms by which CRF modulates the hypothalamic-pituitary-gonadal (HPG) axis are not well understood. In order to verify whether CRF is able to directly influence luteinizing hormone-releasing hormone (LHRH) secretory activity at the level of the medial preoptic area (MPOA), CRF was chronically or acutely injected bilaterally into this hypothalamic area. Ten days before the experiments, female rats were implanted with a permanent double-guide cannula which was stereotaxically positioned close to the MPOA. Chronic administration of rat CRF (rCRF) was accomplished by means of two miniosmotic pumps connected to double internal cannula. Acute bilateral infusion of rCRF into the MPOA was performed in unrestrained ovariectomized (OVX) rats and during the afternoon of proestrus. Ten minutes before rCRF treatment, antagonists of opioid receptors (mu, mu 1, or kappa) were infused bilaterally into the MPOA. Hypothalamic LHRH release as well as circulating gonadotropins were determined using a push-pull cannula implanted into the median eminence (ME), and a catheter connected to the jugular vein, respectively. Chronic rCRF treatment in the MPOA decreased (p < 0.05) plasma LH levels but did not modify follicle-stimulating hormone release in OVX rats. A significant inhibition of LH secretion was first observed 80 min after the acute rCRF infusion into the MPOA; pretreatment with nor-Binaltorphimine (antagonist of kappa-receptors) did not measurably attenuate this effect. In contrast, bilateral administration of beta-Funaltrexamine (antagonist of mu-opioid receptors) or naloxonazine (mu 1-antagonist) partially attenuated the inhibitory effect of rCRF on plasma LH levels. Similarly, injections of rCRF bilaterally into the MPOA suppressed hypothalamic LHRH release into the ME and this effect was partially reversed by a previous administration of opioid mu- or mu 1-receptor antagonists. In contrast to rCRF injection into the MPOA, administration of rCRF into the paraventricular nucleus the arcuate nucleus of the hypothalamus and directly into the ME were without significant effect on hypothalamic LHRH release in proestrus rats. In conclusion, the present data show that from among the hypothalamic sites tested, only the MPOA proved susceptible to CRF-induced alteration of LHRH neuronal activity during proestrus afternoon in rats. The release of opioids from nerve terminals located in the MPOA, which in turn binds and activates mainly type mu 1-receptors, might contribute to this inhibitory influence of CRF on LHRH release in the infundibular system.

Hypothalamic LH-RH release after acute and chronic treatment with morphine studied in a combined in vivo/in vitro model

Rats were treated with the opiate agonist, morphine, and the release of luteinizing hormone-releasing hormone (LH-RH) from their hypothalami was studied in vitro. Within 16–24 h after morphine treatment, basal LH-RH release rates were observed to be higher compared to those from hypothalami derived from opiate-naive rats, suggesting that dependence had occurred in the neural mechanisms underlying LH-RH release. Maintenance of tissues exposed to morphine in vivo in medium containing morphine in vitro did not alter the increased basal release of LH-RH, but because this was significantly greater than control rates, tolerance is not believed to have occurred. Addition of the opioid antagonist naloxone in vitro resulted in a 220% increase in the release of LH-RH by hypothalami exposed to morphine for 48 h in vivo, whereas it caused a 50% reduction in LH-RH release from tissues exposed to morphine for 96 h in vivo. This latter result shows parallels with our previous finding that naloxone paradoxically decreases serum LH levels of chronically morphine-treated rats. In view of recent evidence for presynaptic feedback inhibitory effects operating on opioid neurons, it is suggested that, following chronic exposure to morphine, the opioid neurons which normally inhibit LH-RH neurons are inhibited; upon treatment with naloxone, they are disinhibited and release more opioid peptides which then act to switch off LH-RH neuronal activity.

Naloxone stimulation of in vivo LHRH release is not diminished following ovariectomy.

The effects of an opiate receptor antagonist, naloxone, on the in vivo release of luteinizing hormone releasing hormone (LHRH) in ovariectomized and intact female rats were examined using push-pull perfusion. Hypothalamic LHRH release rates were determined before and after naloxone (2.5 mg/kg s.c.) or saline vehicle injection in rats during metestrus or 4 or 8 days following ovariectomy. Naloxone was found to be equally effective in significantly (p less than 0.05) stimulating LHRH release in all three treatment conditions. In animals that were fitted with atrial catheters instead of push-pull cannulae, naloxone administration led to significant increases in peripheral LH levels in metestrous and ovariectomized rats. Peripheral follicle-stimulating hormone levels were unaffected by naloxone. These results suggest that opioid inhibitory tone is not diminished during pituitary escape from ovarian negative feedback in adult female rats. Our findings are not consistent with the hypothesis that ovarian negative feedback regulation of LH secretion is serially mediated by endogenous opioid peptide neurons in these animals. Rather, it is proposed that opioid inhibition of LHRH release and ovarian negative feedback may operate in parallel to control LH secretion in the female rat.

The effect of luteinizing hormone releasing hormone on the copulatory behavior of hyperprolactinemic male rats

The present study was undertaken to test the hypothesis that the deficits in copulatory behavior observed in hyperprolactinemic male rats may be related to a reduction in hypothalamic release of luteinizing hormone releasing hormone (LHRH). Adult male Fischer 344 rats were made hyperprolactinemic by ectopic pituitary grafts or were sham operated and 30 min prior to being tested for copulatory performance received a single subcutaneous injection of 500 ng LHRH, 100 ng LHRH, or saline. On different occasions, testosterone (T) levels were measured in plasma collected 30 min following identical treatments. Plasma prolactin (PRL) levels were determined in samples collected 30 min after injection of 500 ng LHRH. Pituitary grafting produced the expected, significant increase in plasma PRL levels and significant deficits in copulatory behavior. Treatment of hyperprolactinemic subjects with 500 ng LHRH significantly reduced both the time to first intromission and the time to ejaculation to times comparable with those of sham-operated subjects. The 100-ng dose produced a significant reduction in mount frequency. Plasma T levels were significantly elevated following either dose of LHRH. These results demonstrate that exogenous LHRH can restore normal copulatory performance in hyperprolactinemic male rats and support the hypothesis that a reduction in hypothalamic LHRH release is responsible for the behavioral deficits observed in those animals.

Effect of exogenous luteinizing hormone-releasing hormone on hypothalamic pituitary function in women with ovarian failure

Pituitary luteinizing hormone (LH) pulse frequency and amplitude were assessed as an indirect indicator of hypothalamic luteinizing hormone-releasing hormone (LH-RH) release in women with evidence of ovarian failure. Exogenous LH-RH (20 micrograms) was administered intravenously every 2 hours for 48 hours to determine the effect on pituitary LH release and the hypothalamic pulse generator for LH-RH secretion. This study design was used to investigate the possibility of an ultrashort negative feedback of LH-RH upon the synthesis and release of endogenous LH-RH. A wide range of LH pulse frequencies (8 to 28 pulses/24 hours) was present in these women. There was no discernible inhibition of hypothalamic LH-RH pulse frequency during or following exogenous LH-RH administration. Mean peripheral LH levels were significantly increased during exogenous LH-RH administration (P = 0.0038), reflecting both an increased baseline and an augmented pituitary LH response to the exogenous LH-RH. There were no differences found in LH pulse amplitude before and after LH-RH treatment. These data indicate that pituitary LH secretion in women with ovarian failure can be further stimulated by exogenous LH-RH. However, there was no evidence for inhibition of either pituitary LH secretion or hypothalamic LH-RH release using this administration schedule of exogenous LH-RH.

The effect of hyperprolactinemia produced by transplantable pituitary MtTW15 tumor cells in male rats on hypothalamic luteinizing hormone-releasing hormone release in vitro: effects of naloxone and K+.

Although hyperprolactinemia has been reported to decrease reproductive function in male rats, the mechanism of these effects is not fully understood. We examined the effects of chronic hyperprolactinemia and castration on the LHRH content of the medial basal hypothalamus (MBH) and on the basal and evoked in vitro release of LHRH from the MBH-preoptic area (POA). Adult Wistar-Furth male rats were inoculated with MtTW15 tumor fragments; 3 weeks later half of the rats were castrated. Hyperprolactinemic (H) and normoprolactinemic (N) rats were decapitated 2 weeks later to measure MBH LHRH and serum PRL and LH levels. Elevated PRL levels (greater than 2 micrograms/ml) resulted in significantly increased MBH LHRH stores. Castration caused a 57% depletion of MBH LHRH in N rats; in castrated H rats the MBH LHRH content was also reduced by 40%, a significantly lesser extent. Although serum LH levels in intact H rats were only slightly reduced, postcastration LH hypersecretion was significantly attenuated. In a parallel study, the LHRH release rate was assessed by in vitro perfusion of the MBH-POA. The basal LHRH release rates of intact N and H rats were similar. Castrated N rats released LHRH at a reduced rate (50%; P less than 0.01), whereas in castrated H rats the LHRH release rate was reduced by 20%, which corresponded with the partial depletion of the MBH LHRH content in these rats. To examine the possibility of opiate involvement, LHRH release evoked by two consecutive naloxone (NAL) infusions (1 mg/ml for 30 min) was studied. The two NAL infusions resulted in two similar significant increments of LHRH in the MBH-POA of intact N and H rats. However, castration produced different effects on the NAL-induced LHRH release. First, the second NAL pulse was not effective in stimulating LHRH release from the MBH-POA of N and H castrated rats. Further, the first NAL infusion elicited a significant increase in LHRH output from the MBH-POA of N and H castrated rats, but it was significantly lower in comparison with that in their respective intact counterparts. In addition, the NAL-induced LHRH response was higher from the MBH-POA of castrated H than that in castrated N rats. These studies show that neither basal nor evoked LHRH output in vitro is affected by severe and chronic hyperprolactinemia produced by MtTW15 pituitary tumor cells in intact male rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Hypothalamic and pituitary enzymatic degradation of luteinizing hormone-releasing hormone during the 4-day estrous cycle of the rat. Assessment by high-performance liquid chromatography.

Luteinizing hormone-releasing hormone (LHRH) degrading activity may be of physiological significance as a mechanism capable of partial regulation of hypothalamic LHRH release as well as LHRH levels at the gonadotroph. The possibility of cyclic fluctuations in LHRH-degrading activity was investigated in female rat hypothalami and pituitaries. These tissues were collected at selected time points during the 4-day estrous cycle, homogenized, and centrifuged at 100,000 g. Supernatants were incubated with synthetic LHRH, the reactions terminated, and the decapeptide and its products separated by high-performance liquid chromatography. Degradation of LHRH incubated with active cytosol was estimated by comparison of integrated LHRH peak area with that from incubations with heat-inactivated cytosol. Hypothalamic LHRH degradation was depressed during the latter hours of diestrus 2, a time during which the LHRH content in the hypothalamus has been reported to be increasing. From diestrus 24.00 h to proestrus 15.00 h, there was a significant increase in degrading activity. This was then followed by a decline from 15.00 to 18.00 h proestrus; at the time of the LH surge, the activity had not undergone significant increase in comparison to 18.00 h. Pituitary LHRH degradation was significantly increased during the 6-hour period preceding the surge, but was significantly depressed at the surge. The hypothalamic reduction in activity associated with diestrus 2 as well as the hypothalamic and pituitary reductions associated with proestrus may represent a permissive effect allowing increased LHRH accumulation in the hypothalamus and its prolonged action in the pituitary.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of ethanol on hypothalamic luteinizing hormone-releasing hormone (LHRH) in the male rat. An immunocytochemical study.

These studies were designed to determine if the acute alcohol-induced decreases in luteinizing hormone (LH) seen in previous studies using rats could be due to an inhibitory effect of ethanol (ETOH) on hypothalamic LHRH release. Thus, effects of multiple injections of ETOH on the relative amount of immunoreactive LHRH fibers in the hypothalamus and median eminence (ME) of castrate and intact male rats were determined immunocytochemically. Brains were removed following cardiac perfusion of 10% phosphate-buffered formalin. A block containing the hypothalamus with the ME was isolated from each brain, then postfixed in Bouin's solution. Paraffin sections were rehydrated and stained for LHRH with the peroxidase-antiperoxidase technique using an antiserum to synthetic LHRH conjugated to bovine serum albumen. Differences visualized immunocytochemically between saline-treated intact and castrate rats indicated that the LHRH content of the ME was markedly depleted after castration. Conversely, castrate rats treated with ETOH showed only a slight reduction in immunoreactive LHRH fibers. In ETOH-treated intact animals, the LHRH fiber content of both the hypothalamus and ME appeared to be slightly greater than the saline-treated intact controls. Thus, these data support the hypothesis that ETOH diminishes LHRH release, and hence provides an explanation for the depressed plasma LH levels observed in ETOH-treated intact and castrate rats.

Effects of hypothalamic arcuate nucleus lesions on pulsatile luteinizing hormone concentration in ovariectomized rats.

We investigated the effects of hypothalamic arcuate nuclei destruction on the postovariectomy rise in plasma luteinizing hormone (LH) concentration and the pulsatile LH release mechanism in ovariectomized rats. Rats were injected with 1, 2, or 4 mg/g body wt of L-monosodium glutamate (MSG) on Days 1, 3, 5, 7, and 9 of life to lesion the arcuate nuclei. They were then ovariectomized as adults and used 2 or 4-8 weeks later. Serial blood sampling at 10-min intervals and measurement of plasma LH concentration revealed elevated plasma LH levels which fluctuated in a pulsatile fashion in all control and 1 and 2 mg/g/MSG-treated rats. In 4 mg/g MSG-treated rats, plasma LH levels were lower than in controls of both time periods after ovariectomy due to a decrease in the amplitude and/or frequency of LH pulses. Phenobarbital was administered to all 4- to 8-week ovariectomized rats to block endogenous pulsatile LH release. In phenobarbital-blocked rats, three sequential iv injections of LH releasing hormone (LHRH) caused substantial elevations in plasma LH concentrations even in the 4 mg/g MSG-treated animals which had low plasma LH concentrations during control bleedings prior to the injection of phenobarbital. The results indicate that the postovariectomy rise in plasma LH concentration and the associated pulsatile LH release mechanism are functional in rats with extensive arcuate nucleus lesions. The diminution in the rise in plasma LH levels and the decreased amplitude and/or frequency of LH pulses in the MSG-treated rats is likely due to a diminution in hypothalamic LHRH release.

A paradoxical castration effect on LH-RH levels in male rat hypothalamus and serum

Serum and hypothalamic luteinizing hormone releasing hormone (LH-RH) was lowered in young mature male rats after castration. Testosterone injections raised the hypothalamic LH-RH content significantly. The mean value of serum LH level was elevated by testosterone, but not significantly. Hypothalamic LH-RH content was also lowered by hypophysectomy. In this circumstance, testosterone injections significantly increased LH-RH content. These results suggest that there may be a positive feedback of testosterone upon the hypothalamic LH-RH release and synthesis mechanisms.