Effect of nitric oxide synthase inhibitors on preventing ethanol-induced suppression of the hypothalamic-pituitary-gonadal axis in the male rat

Ethanol (EtOH) suppression of the hypothalamic-pituitary-gonadal (HPG) axis results in broad reproductive malfunction. In the HPG axis, the suppressive effects of EtOH are manifested by decreased serum testosterone, reduced testicular luteinizing hormone (LH) receptor numbers, lowered serum LH and pituitary beta-LH mRNA levels (in castrated animals), and impaired luteinizing hormone releasing hormone (LHRH) release from the hypothalamus. Increasing evidence has suggested that nitric oxide (NO) plays a role in regulation of the HPG axis. NO was shown to stimulate LHRH secretion from the hypothalamus and to have variable effects on LH release from the pituitary. At the gonadal level, NO is inhibitory to testosterone production. NO may directly inhibit some testicular steroidogenic enzymes. To investigate the effect of EtOH, NO, and their interaction on the male HPG axis, three NO synthase (NOS) inhibitors, N(G)-nitro-L-arginine methyl ester, N(G)-nitro-L-arginine, and 7-nitro indazole were used to study overall HPG function in the presence and absence of EtOH. Animals were given intraperitoneal injections of saline, EtOH, various NOS inhibitors, or EtOH, along with NOS inhibitors 2 hr before sacrifice. Serum testosterone and LH concentrations, pituitary beta-LH mRNA levels, hypothalamic LHRH mRNA levels, and LHRH content were determined. It was found that blocking NOS by these NOS inhibitors prevented EtOH-induced suppression of testosterone and, in some cases, serum LH. However, this was not accompanied by concurrent changes with NOS blockade on LHRH mRNA, hypothalamic pro-LHRH or LHRH content or pituitary LH beta mRNA levels. It appears that the protective effect of NOS blockade was largely, although not completely, due to a direct effect at the gonadal level.     

Effects of the opioid antagonist naltrexone-estrone azine on the luteinizing hormone-releasing hormone induced release of luteinizing hormone from the pituitary glands of ovariectomized rats

The effects were studied of in vivo administration of the new opioid antagonist-estrogen hybrid, naltrexone-estrone azine (EH-NX), on subsequent luteinizing hormone-releasing hormone (LHRH)-stimulated luteinizing hormone (LH) release by the pituitary gland in vitro. It is well known that administration of estrogen exerts negative and positive effects on the pituitary LH response to LHRH, respectively after short-term and long-term treatment. Rats were injected subcutaneously with either 17 beta-estradiol-3-benzoate (EB), EH-NX or oil on days 18 and 19 (long-term treatment), and on day 21 (short-term treatment) following ovariectomy. Twenty minutes later the animals were killed and the pituitary glands were incubated in the presence of LHRH (1000 ng/ml) for 4 h. Whereas short-term treatment with EB on day 21 did not affect LH release in vitro, EH-NX significantly decreased the pituitary LH response to LHRH in oil pretreated rats. This inhibitory effect was partially blocked by the opioid antagonist naltrexone. After long-term EB or EH-NX, followed by short-term oil treatment, the pituitary LH response to LHRH was increased considerably, compared to the long-term oil controls. These observations demonstrate that the opioid antagonist estrogen hybrid EH-NX has estrogenic activity at the level of the pituitary gland. This hybridized drug is more effective in time than EB and an equimolar amount of EH (estrone hydrazone) to induce the negative estrogenic effect.     

Induction of feline acquired immune deficiency syndrome by feline leukemia virus: immuno- and neuroendocrine dysfunctions

Young cats, when chronically infected with feline leukemia virus (FeLV), developed feline acquired immune deficiency syndrome (FAIDS). The syndrome was associated with a sequence of dysfunctions in the hypothalamic-pituitary-gonadal (HPG) and the immune system, manifested in the reduction of luteinizing hormone-releasing hormone (LHRH), follicle stimulating hormone (FSH), luteinizing hormone (LH), and testosterone in blood plasma. The average FSH and LH (in plasma or lymphocyte), testosterone, and LHRH concentrations in the 20 FeLV-infected cats were measured by radioimmunoassay. The results were compared with those of the 12 control cats that were not FeLV-infected. Four weeks after infection, the plasma LHRH concentration in the infected cats showed a 43% reduction. Five to six weeks after infection, the content of FSH and LH in lymphocyte was reduced by 50% and 28%, respectively, whereas, the plasma FSH and LH was reduced by 52% and 42%, respectively. A significant reduction in testosterone content was detected at Week 11 of infection. The onset of the immuno- and neuroendocrine dysfunctions in FAIDs cats followed this sequence: hypothalamus, lymphocyte, pituitary, adrenal gland, and gonads. Indirect immunofluorescence assay showed the presence of FeLV cytoplasmic antigens in the fibers of the hypothalamic preoptic region and the Leydig cells. The possible causal relationship between the dysfunction of the lymphocyte and HPG systems and the presence of FeLV was discussed.     

Alterations in the opioid control of LHRH release from hypothalami isolated from aged male rats

Several lines of evidence have suggested that the opioid control of gonadotropin secretion in the male rat is altered with aging. Because neural control of gonadotropins is mediated through luteinizing hormone releasing hormone (LHRH) secreting neurons, we examined the postulated changes in the opioid control of gonadotropins more directly by studying isolated hypothalamic fragments in vitro. Hypothalami from young (75-90 days) and old (18-20 months) males were examined for their ability to release LHRH when incubated with increasing doses of naloxone in a semi-static culture system. Serum concentrations of testosterone and luteinizing hormone (LH) in the donor animals were both significantly lower in old male rats compared with young males. Basal secretion of LHRH was similar in both age groups. Two-way repeated measures ANOVA indicated that naloxone stimulated a significant dose-dependent increase in the release of LHRH into the media. ANOVA also indicated a significant effect of age. We conclude that the changes in the endogenous opioid systems reported to occur with aging are, in fact, linked to differences in LHRH secretion and thus to differences in the dynamic relationship between testosterone and LH in older male rats.     

Effects of external cadmium ions on excitation-contraction coupling in rat soleus fibres

Administration of 4 mg of the antisteroid RU486 over 8 consecutive days to adult male rats dissociated in vivo and in vitro gonadotrophin secretion, increasing FSH and decreasing LH secretion. In subsequent experiments we evaluated the involvement of testicular or adrenal secretory products, as well as hypothalamic LHRH, in the effects of 4 consecutive days of RU486 treatment on the secretion of gonadotrophins. The first day of RU486 injection was designated day 1, subsequent days being numbered consecutively. Groups of rats injected with oil (0.2 ml) or RU486 (4 mg) were: (i) injected s.c. from day 1 to day 4 with the antiandrogen flutamide (10 mg/kg); (ii) bilateral orchidectomized (ORCH) on day 1; and (iii) bilateral adrenalectomized (ADX) on day 1. Controls were given flutamide vehicle or were sham operated. To ascertain whether the secretion of LHRH is involved in the effects of RU486 on gonadotrophin secretion, we measured the LHRH secretion into the pituitary stalk blood vessels at 1100 h on day 5 in oil- or RU486-treated rats. Additional oil- and RU486-treated rats were injected i.p. with 100 ng LHRH at 1000 h on day 5, or s.c. with 1 mg LHRH antagonist (LHRH-ANT) at 1000 h on days 2 and 4. Controls were given saline. All animals were decapitated at 1100 h on day 5, trunk blood collected and serum stored frozen until FSH, LH and testosterone assays.%While ADX had no effect on FSH and LH secretion in either oil- or RU486-treated rats, the removal of androgen negative feedback with flutamide treatment or by ORCH substantially increased serum levels of FSH and LH in both oil- and RU486-treated rats, and thus annulled the effects of RU486. No differences in pituitary stalk plasma LHRH concentrations were found between oil- and RU486-treated rats. Injection of LHRH increased serum FSH and LH concentrations in oil-treated rats but only, and to a lesser extent, LH concentrations in RU486-treated rats. Treatment with LHRH-ANT decreased serum concentrations of FSH and LH in both oil- and RU486-treated rats. These results suggest that RU486 inhibited LHRH-stimulated LH secretion at the pituitary level, and that FSH secretion increased in response to a reduction in the negative feedback of androgen.     

Interaction of estradiol and LHRH on LH release in rhesus females: evidence for a neural site of action

The effects on LH release of infusing luteinizing hormone-releasing hormone (LHRH 80 mug/20 min) into the third ventricle, the pituitary, and the peripheral circulation were compared in spayed rhesus monkeys. Within 30 min after iv administration, serum LH concentrations increased to twice to preinfusion levels, and by 120 min declined to original values. Intraventricular or intrapituitary infusions of LHRH resulted in similar LH increments, but the peaks occurred somewhat later (70 to 90 min) and the elevations persisted beyond 200 min. Estradiol-17beta (E2) administered by a sc silastic capsule caused a 5-fold increase in serum E2 within 1 h and reduced serum LH levels by 65% within 4 h. The LH release caused by intrapituitary LHRH was significantly suppressed by maintaining for 72 h E2 concentrations near 100 pg/ml, a level inadequate for stimulating an LH surge. A comparable E2 treatment before intraventricular infusion of LHRH, however, did not inhibit LH release. This difference between the effects of intrapituitary and intraventricular LHRH was demonstrable only in E2-treated monkeys. Moreover, the release of LH after intraventricular infusion of LHRH in E2-treated females was blocked (P less than 0.001) by a single iv injection (90 min before LHRH) of haloperidol (1 mg/kg BW) or phentolamine (5 mg/kg), but was not altered by phenoxybenzamine (3 mg/kg) or propranolol (5 mg/kg). Without E2 pretreatment, LH release after intraventricular LHRH was enhanced by each drug. Phentolamine, injected into both E2- and non-E2-treated monkeys 90 min before an intrapituitary infusion of LHRH had no demonstrable effects on the patterns of serum LH. Our interpretation of these data is that E2 at a concentration below the level that triggers an LH surge has a dual action on LHRH-induced LH release in monkeys: an inhibitory effect exerted directly on the pituitary and a stimulatory effect on the brain. Furthermore, the paradoxical effects of the drugs with and without E2 are due to the involvement of two distinct neuronal systems. The postulated neural effects of both E2 and these drugs can be explained either by an increase in the quantity of injected or secreted LHRH which ultimately binds to LH-secreting cells or by the release of additional endogenous LH-stimulating agents together with ventricular LHRH.     

Reversal of ethanol-induced testosterone suppression in peripubertal male rats by opiate blockade

Teenage drinking is a major problem in the United States, as well as abroad. Besides psychosocial implications, ethanol (EtOH) has detrimental effects on the reproductive system. Clinical problems associated with reduced reproductive hormones include osteoporosis, decreased muscle function, anemia, altered immune function, prostate involution, and decreased reproductive abilities. Education coupled with strategies aimed at preventing these deleterious consequences even in the face of continued EtOH intake is extremely important. We have tested the possibility that naltrexone, a drug currently used in patients to decrease alcohol craving, might also prevent the fall in the male hormone, testosterone, caused by EtOH exposure. Rats aged 35 days old (prepubertal), 45 days old (midpubertal), and 55 days old (late pubertal) were injected (intraperitoneally) with either saline, EtOH, naltrexone, or EtOH plus naltrexone. In the two older age groups, EtOH significantly suppressed testosterone, which was prevented by administration of naltrexone. In the youngest animals, there was no treatment effect presumably due to low basal levels of testosterone. EtOH similarly reduced luteinizing hormone (LH), but this suppression was not prevented by naltrexone. There was no consistent effect of any treatment on hypothalamic concentration of pro-LH releasing hormone (RH) (LHRH), LHRH, or on steady-state levels of LHRH mRNA. We conclude that, as animals progress through puberty, EtOH suppresses LH and testosterone. The testosterone decline can be prevented by opiate blockade with naltrexone, an effect primarily seen at gonadal level. Thus, naltrexone, a drug already used clinically to reduce EtOH intake, also has protective physiological effects on the endocrine system.     

Effect of infarct artery patency on prognosis after acute myocardial infarction. The Survival and Ventricular Enlargement Investigators

In this study, adult male rats were injected intraperitoneally with a single dose of serotonin (5-hydroxytryptamine, 5HT; 10 mg kg-1 bodyweight) for 2 h or 18 h, or daily with graded doses of 5HT (0.1-10 mg kg-1) for four days before being killed. Serum and testicular interstitial fluid (IF) concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone and immunoreactive-inhibin were measured by radioimmunoassay, and one testis was removed for histological examination. At 2 h after a single injection, 5HT caused a significant inhibition of serum concentrations of LH and inhibin, recovered IF volume and intratesticular testosterone concentrations; testis weight and serum concentrations of testosterone and FSH were unaffected. At 18 h after injection, all parameters had returned to normal, with the exception of intratesticular testosterone concentration which remained lower than normal. The lowest 5HT dose (0.1 mg kg-1) had no effect on any parameter following four daily injections. At a dose of 1.0 mg kg-1 5HT, there was a four-fold increase in the concentration of serum LH, but testis weight, recovered IF volume, testosterone and inhibin concentrations and serum concentrations of FSH were not significantly affected. At the highest dose of 5HT (10 mg kg-1) after four daily injections, testis weight decreased, and IF volume increased nearly three-fold. Testis concentrations of inhibin and serum testosterone were reduced, whereas serum concentrations of both LH and FSH were elevated; intratesticular testosterone concentrations did not differ from controls. Only at the highest dose of 5HT was disruption to the seminiferous epithelium observed, with focal damage ranging in severity from increased degeneration of spermatogenic cell profiles, to complete loss of the germinal epithelium; however, many tubule profiles displayed completely normal spermatogenesis. The acute IF volume reduction and spermatogenic disruption in 5HT-treated rats were consistent with localized ischaemia due to constriction of the testicular arterial supply. The eventual increase in IF volume observed after 5HT treatment appeared to be secondary to the loss of germ cells. Although 5HT also inhibited pituitary LH release and Leydig cell steroidogenesis, these effects appeared to play only a minor role in the induction of spermatogenic damage.     

Endocrine therapy of transsexualism and potential complications of long-term treatment

Physiological principles of the interrelationship of sex hormones and their regulation are the foundation of understanding appropriate treatment of the transsexual patient. While both genetic males and females have estrogens and androgens, the quantitative sex hormone production is genetically predetermined by sex hormone production both in the gonads and via peripheral conversion of hormone precursors to sex steroids. Sex hormones exert a negative feedback on the hypothalamus and pituitary gland whereby gonadotropin-releasing hormone (GnRH), pituitary luteinizing hormone (LH), and follicle-stimulating hormone (FSH) are regulated or suppressed by the endogenous levels of these hormones. Sex hormonal therapy induces attenuated GnRH stimulation of LH and FSH causing a reduction of serum sex hormone levels. It is clear that estrogen as well as androgen therapy have a dual role: (i) induction of feminization or virilization and (ii) suppression of the hypothalamic-pituitary-gonadal axis leading to a reduction of endogenous estradiol or testosterone secretion. Cross-sex hormonal treatment may have substantial medical side effects. The smallest dosage of hormonal therapy compatible with the above clinical aims should be used.     

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-1 beta was the most potent inhibitor of pituitary LH secretion; interleukin (IL)-1 alpha and tumor necrosis factor (TNF) alpha 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-1 beta, and this was supported by the demonstration that IL-1 beta 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 mu 1 receptor subtype was required to transmit the cytokine signal. Furthermore, icv IL-1 beta upregulated hypothalamic POMC mRNA and increased the concentration and release of beta-endorphin, the primary ligand of mu 1 receptors. We have obtained evidence that IL-1 beta also enhanced the gene expression and concentration of tachykinins, a family of nociceptive neuropeptides in the hypothalamus. Blockade of tachykinergic NK2 receptors attenuated IL-1 beta induced inhibition of LH secretion. Collectively, these results demonstrate that IL-1 beta, 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.     

Age-dependent effects of hippocampal muscarinic receptor blockade on memory-based learning in the developing rat

In the male rat, testosterone has been shown to regulate gonadotrophin synthesis and secretion under experimental conditions such as castration or gonadotrophin-releasing hormone (GnRH) antagonist with or without testosterone. The present study aims at clarifying the effects of non-steroidal antiandrogens, Casodex and flutamide, and ethane dimethane sulphonate (EDS) on the regulation of gonadotropin synthesis and secretion. To enable a direct comparison within this study to expected effects of testosterone, a GnRH antagonist-treated group and a castrated group were included. The gene expression of the subunits was correlated with changes in the pituitary and plasma content of immunoreactive luteinizing hormone (LH) and follicle-stimulating hormone (FSH), free subunits and pituitary content of in vitro bioactive LH and FSH. Groups of ten male rats each received the following treatments for 7 days: (1) vehicle; (2) castration; (3) EDS (75 mg/kg); (4) GnRH antagonist (Cetrorelix 250 micrograms/kg/day), (5) Casodex (20 mg/kg/day) or (6) flutamide (20 mg/kg/day). The effectiveness of testosterone deprivation was demonstrated by the reduction of weight in androgen-dependent organs such as epididymides and seminal vesicles in the treated groups. Treatment with flutamide, EDS or castration significantly increased (p < 0.05) serum levels of LH, FSH and alpha-subunit, whereas serum gonadotrophin levels were decreased in the GnRH antagonist-treated group. alpha-Subunit mRNA levels were elevated in the castrated, EDS and flutamide group and LH-beta mRNA levels were increased in the castrated and EDS group. FSH-beta mRNA levels were increased in the castrated group and decreased in the GnRH antagonist group, but remained unchanged in the flutamide and EDS group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hypothalamus-pituitary-ovarian axis in cyclic rats lacking progesterone actions

Antagonizing diestrous progesterone actions in cyclic rats by s.c. injections of the antiprogesterone RU486 (2 mg twice a day from metestrus through proestrus) increased LH and decreased FSH basal serum concentrations. Ovariectomy at metestrus (0800 h) increased serum levels of both gonadotropins in controls and reversed the RU486-induced dissociation of basal gonadotropin secretion. RU486-dissociated gonadotropin secretion is also dependent upon LHRH, since treatment (s.c.) with 1 mg GnRH antagonist (ORG 30276) twice a day on metestrus and diestrus completely prevented both the RU486-induced increase in LH and the decrease in FSH serum concentrations. The LHRH content in the medial basal hypothalamus and median eminence increased on proestrous morning in RU486-treated rats. The LH pituitary response to an exogenous i.v. bolus of 25 ng LHRH (Peninsula 7201; Peninsula Laboratory, Inc., Merseyside, UK) at 1700 h on diestrus was enhanced in rats treated with RU486. No differences in pituitary FSH response were noted with respect to oil-injected rats. The pituitary content of both gonadotropins decreased in RU486-treated rats on proestrous morning. All these effects due to RU486 in cyclic rats were reversed by ovariectomy. Testosterone serum levels increased significantly from diestrus onward, and the estradiol concentration increased on proestrous morning in RU486-treated rats. Ovariectomy as well as LHRH antagonist treatment eliminated the effects of RU486 on ovarian steroid production. Moreover, antiestrogen tamoxifen treatment reversed RU486-dissociated gonadotropin secretion, while antiandrogen flutamide treatment had no effect. The results of this experiment have confirmed previous findings that RU486 treatment dissociates basal gonadotropin secretion in cyclic rats. In addition, the present results show that: (1) this effect of RU486 is not due to a direct effect of this compound or to the blockade of progesterone action at a central level; (2) the effect of RU486 on pituitary gonadotropin secretion depends on ovarian substances other than progesterone and LHRH, since it is reversed by ovariectomy and completely abolished by LHRH antagonist treatment; (3) the reduction in FSH serum levels in rats treated with RU486 seems to be exerted by inhibin and estradiol at the pituitary level by reducing FSH synthesis and secretion; and (4) the hypersecretion of LH in rats treated with RU486, as compared to that resulting from ovariectomy, seems to be the consequence of, first, a lack of progesterone inhibitory action on LH secretion, and, second, an inappropriate feedback system involving increased hypothalamic LHRH activity and pituitary sensitivity to LHRH of moderately high levels of estradiol in the presence of abnormally high levels of testosterone.     

Lineage commitment of HLA-DR/CD38-defined progenitor cell subpopulations in bone marrow and mobilized peripheral blood assessed by four-color immunofluorescence

ONO-9302 [epristeride; (-)-17beta-(tert-butylcarbamoyl)androsta-3,5-diene-3-carboxy lic acid] is a novel inhibitor of steroid 5alpha-reductase. We studied in vitro and in vivo effects of ONO-9302 on the rat prostatic tissue in comparison with those of the anti-androgen allylestrenol. ONO-9302 inhibited the rat prostatic enzyme with an IC50 value of 11 nM, whereas allylestrenol was about 80,000-fold less potent. The growth of ventral prostate, which was induced by the subcutaneous injection of testosterone propionate in the castrated rats, was significantly reduced by ONO-9302 at oral doses of 1-100 mg/kg/day. Allylestrenol showed a significant effect only at a dose of 100 mg/kg/day. In mature male rats, ONO-9302 significantly reduced the ventral prostate weight at doses of 10-100 mg/kg/day and decreased prostatic 5alpha-dihydrotestosterone (DHT) content associated with a rise in testosterone (T) content at doses of 0.1-100 mg/kg/day. Plasma hormone levels (i.e., T, DHT, luteinizing hormone (LH) and follicle stimulating hormone (FSH)) were not altered significantly. Allylestrenol significantly reduced the ventral prostate weight at doses of 10-100 mg/kg/day. However, unlike ONO-9302, allylestrenol reduced both the prostatic DHT and T contents and also lowered plasma T, DHT, LH and FSH levels at a dose of 30 mg/kg/day. These results suggest that ONO-9302 reduces the prostatic growth by inhibiting the conversion of T to DHT in the prostate without lowering blood T level unlike anti-androgen drugs.     

Long-term results of cobalt 60 curietherapy for uveal melanoma

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, (alpha 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) alpha. 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.     

The effect of LHRH and TRH on human interferon-gamma production in vivo and in vitro

Accumulating evidence suggests that hypothalamic luteinizing hormone-releasing hormone (LHRH) and thyrotropin-releasing hormone (TRH) are two hypophysiotropic factors which modulate the immune response. The aim of the present study was to determine the in vivo effects of an intravenous bolus of LHRH and TRH on plasma interferon (IFN)-gamma production in five normoprolactinemic women with irregular menstrual cycles. We also determined prolactin (PRL), thyrotropin (TSH), follicle stimulating hormone (FSH), and luteinizing hormone (LH) levels before and after intravenous administration of LHRH and TRH. The results demonstrate that intravenous bolus of LHRH/TRH increases plasma IFN-gamma levels, with the maximum response 45 min after in vivo administration of hypothalamic peptides and after peak levels of adenohypophyseal hormones (PRL: 15 min; TSH: 30 min; FSH: 30 min; LH: 30 min). In order to investigate a possible direct action of hypothalamic hormones on immune cells, we also evaluated, in the same subjects, the influence of LHRH and TRH on IFN-gamma production by human peripheral blood mononuclear cells (PBMCs), collected before the intravenous administration of the peptides and stimulated in vitro with bacterial superantigen staphylococcal enterotoxin A (SEA) and concanavalin A (Con A). LHRH and TRH, separately and together, significantly enhanced in vitro IFN-gamma production by SEA- and ConA-activated PBMCs. The present results suggest that hypothalamic peptides (LHRH and TRH) directly, and/or indirectly pituitary hormones (PRL, TSH, FSH, and LH) or IL-2, have stimulatory effect on IFN-gamma producing cells and are further evidence of interactions between the neuroendocrine and immune systems.     

Central administration of antisense oligodeoxynucleotides to neuropeptide Y (NPY) mRNA reveals the critical role of newly synthesized NPY in regulation of LHRH release

Compelling evidence shows that the episodic and cyclic secretion of hypothalamic luteinizing hormone releasing hormone (LHRH), the primary stimulator of pituitary LH release, is subject to regulation by neuropeptide Y (NPY). We have reported earlier that sequential treatment of ovariectomized (ovx) rats with estrogen and progesterone to stimulate a preovulatory-type LH surge elevated the levels of both NPY and preproNPY mRNA levels in the hypothalamus concomitant with dynamic changes in LHRH activity. The present study was designed to determine whether these elevations in NPY content and gene expression represent new synthesis of NPY that is crucial to elicit LHRH discharge. Ovx, steroid-primed rats received intracerebroventricular injections of an unmodified 20-mer oligodeoxynucleotide (oligo) complementary to the NPY mRNA sequence. Control rats were injected similarly with either saline or the sense or missense oligos. Results showed that control rats displayed a characteristic surge-type elevation in plasma LH levels that was not affected by the administration of missense or sense oligos. However, in rats injected with the antisense oligo, the steroid-induced LH surge was completely blocked. In an additional experiment, NPY peptide levels were measured in microdissected hypothalamic sites following the injection of antisense or missense oligos. NPY antisense oligo administration blocked the significant increases in NPY levels in the median eminence-arcuate area, the medial preoptic area and lateral preoptic area seen in control rats. These results suggest that sequential ovarian steroid treatment augments NPY synthesis in the hypothalamus and this newly synthesized NPY is critical for induction of the LHRH and LH surge.     

Melatonin inhibits naloxone-induced luteinizing hormone release in ovariectomized estrogen-primed rats

The present study aimed to examine the effect of melatonin on naloxone-induced luteinizing hormone (LH) secretion in ovariectomized estrogen-primed rats. A single intracerebroventricular (i.c.v.) injection of naloxone (mu opioid receptor blocker, 15 micrograms) or an intravenous (i.v.) injection of LH-releasing hormone (LHRH, 50 ng/kg) elicited a transient and significant increase in the serum LH concentration within 10 min. While an i.c.v. injection of 100 ng melatonin by itself did not change the basal LH release, it almost completely inhibited the naloxone-induced LH release. Melatonin (10 ng) also significantly reduced the effect of naloxone. However, an i.c.v. injection of 100 ng melatonin did not affect the LHRH-induced LH release. In separate experiments, the effect of melatonin on naloxone-induced pulsatile LH secretion was studied in estrogen-treated rats. A continuous i.v. infusion of naloxone (20 mg/kg/h) induced LH pulses in rats treated i.c.v. with saline. An i.c.v. administration of 100 ng melatonin, which by itself did not affect basal LH secretion, significantly reduced the frequency, but not the amplitude, of LH pulses induced by the naloxone infusion. These results show that melatonin has a suprapituitary site of action to inhibit naloxone-induced LH release, and suggest that melatonin has an effect in inhibiting the activity of the hypothalamic LHRH pulse generator, either directly or indirectly, in female rats.     

Bi-level positive airway pressure (BiPAP) ventilation in an infant with central hypoventilation syndrome

OBJECTIVES: To determine the effects of long-term cigarette smoking on the levels of plasma testosterone, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in male adult rats and to examine morphological and histological changes in the testes. MATERIALS AND METHODS: Cigarette smoke was generated by a smoking-machine and 12 rats were exposed to cigarette smoke diluted with 90% air for 60 days (2 h/day). Twelve rats were exposed to room air only under similar conditions as controls. The concentrations of plasma testosterone, LH and FSH were measured before and after exposure using a radio-immunoassay and the testes were examined histologically. RESULTS: In rats exposed to smoke, the mean plasma testosterone level decreased significantly but there were no significant changes in testosterone in the control rats. The mean plasma LH and FSH levels of the two groups did not change significantly after exposure. In rats exposed to smoke, histological examination of the testes showed fewer Leydig cells and degeneration of the remaining cells. CONCLUSION: These results indicate that the decrease in plasma testosterone levels induced by exposure to smoke was not associated with changes in plasma gonadotrophin levels. The decrease in testosterone levels may be related to the toxic effects of smoke on Leydig cells.     

Phenomenon of intrinsic rhythm of luteinizing hormone release from isolated anterior pituitary gland of female rat

The intrinsic nature of rthymic release of luteinizing hormone (LH) of isolated human and rat anterior pituitary gland reported independently by Macro Gambacciani and Xie in 1987 can be more directly demonstrated by a computer programme of Time Series-HSY Hidden Periodic Analytic Approach for continuous monitoring the LH output of the perfusate from a perfusion system with in vitro anterior pituitary of SD female rat. The results are as follows: (1) Under various reproductive conditions the average frequency (min/cycle) and amplitude (ng/ml) of the intrinsic rhythm of LH release were quite different: In proestrous group the frequency and amplitude were the highest, being intermediate in the ovariectomized group and lowest in the lactation group. (2) The intrinsic rhythm of LH release could be changed by either peptide or steroid hormones. In proestrous group with 30 min of gonadotropin-releasing hormone (GnRH), stimulation would reduce both frequency and amplitude. In case of lactation, the frequency was unchanged, but amplitude lowered, while in the ovariectomized rat pituitary, the 30 min GnRH stimulation decreased the frequency of release only. The intrinsic rhythm of the LH release could also be influenced by steriod hormones (Ru486 and Anordrin). With 120 min before removal of the anterior pituitary gland the rats receiving i.m. injection of Ru486 (2 mg/kg bw) or Anordrin (2 mg/kg), the results showed that Ru486 decreased frequency, while Anordrin decreased only the frequency to a less extent, both without amplitude affected. (3) Verapamil and EGTA added to the perfusion system did not abolish but only decreased the rhythmic phenomenon by using proestrous pitutary. This suggests that participation of Ca2+ may take place in the intrinsic release of LH. The above results indicated that the intrinsic rhythm of LH release of isolated anterior pituitary gland is different from various reproductive hormonal conditions and capable of being modified by exogenous hormones. The physiological function of the intrinsic rhythm of LH release of anterior pituitary gland remains to be elucidated.