Inducible nitric oxide synthase (iNOS) is a transcriptionally regulated enzyme that synthesizes nitric oxide from L-arginine that has a key role in the pathophysiology of systemic inflammation and sepsis. Transgenic animals with a null mutation for the iNOS gene are resistant to hypotension and death caused by Escherichia coli lipopolysaccharide (LPS). The regulation of peripheral iNOS has been well studied in sepsis, but little is known about iNOS regulation in the brain during systemic inflammation or sepsis. We know that at baseline there is no detectable iNOS gene expression in the brain, but a detailed neuroanatomical study reveals that early in the course of systemic inflammation there is a profound induction of iNOS messenger RNA in vascular, glial and neuronal structures of the rat brain, accompanied by the production of nitric oxide (NO) metabolites in brain parenchyma and cerebrospinal fluid (CSF). We propose that the spillover of nitrite into the CSF has the potential to be a diagnostic marker for systemic inflammation and sepsis. Pharmacological interventions aimed at regulating iNOS function in the brain might represent a new treatment strategy in sepsis. Brain iNOS may be relevant to the pathophysiology, diagnosis and treatment of systemic inflammation and sepsis.

It has previously been shown that alcohol can suppress reproduction in humans, monkeys, and small rodents by inhibiting release of luteinizing hormone (LH). The principal action is via suppression of the release of LH-releasing hormone (LHRH) both in vivo and in vitro. The present experiments were designed to determine the mechanism by which alcohol inhibits LHRH release. Previous research has indicated that the release of LHRH is controlled by nitric oxide (NO). The Alcohol suppresses reproductive function in humans, monkeys, and small rodents, such as the rat (1-4). In the rat,The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. 3416 chronic administration of alcohol not only inhibits the estrous cycle but it can also delay onset of puberty (4, 5). In conscious animals, administration of alcohol via an indwelling gastric cannula in doses that produce mild intoxication inhibits pulsatile release of luteinizing hormone (LH), but not folliclestimulating hormone, within a few minutes (4). In this situation, the responsiveness of the pituitary gland to acute injection of LH-releasing hormone (LHRH) is unaffected, which shows that the mechanism of this effect is via suppression of the pulsatile LHRH release into the hypophyseal portal vessels that triggers release of LH from the gonadotropes of the adenohypophysis. The interference with estrous cycles and the delayed onset of puberty in the female rat is likely brought about by this suppression by ethanol of LHRH release (5). Secretion of LH is required to stimulate the ovary to produce ovarian steroids responsible for the estrous cycle, and the onset of puberty is consequently delayed.We have recently shown that nitric oxide (NO) controls the release of LHRH both in vivo and in vitro (6). On the basis of in vitro experiments employing incubation of medial basal hypothalamic (MBH) explants in a static incubation system, it has been determined that norepinephrine activates constitutive NO synthase (NOS) in neurons in this region (NOergic neurons) (6, 7). The NO released from these neurons diffuses to LHRH terminals, where it induces the release of LHRH, probably by activating cyclooxygenase 1. The activated cyclooxygenase then converts arachidonate into prostaglandin E2 (PGE2) (8). PGE2 activates adenylate cyclase, causing generation of cAMP, which acts via protein kinase A to evoke exocytosis of LHRH granules into the hypophyseal portal vessels for its delivery to the anterior pituitary gland (9, 10). The LHRH acts on the gonadotropes and causes a pulse of LH release. Support for this theoretical pathway stems from the ability of inhibitors of NOS, such as NG-monomethyl-Larginine, to inhibit LHRH release, whereas releasers of NO, such as sodium nitroprusside (NP), induce LHRH release both in vitro and in vivo (6-9).We have identified the site of inhibitory action of interleukin 1 (IL-1) on LHRH release...

Release of luteinizing hormone (LH)-releasing hormone (LHRH), the hypothalamic peptide that controls release of LH from the adenohypophysis, is controlled by NO Since citrulline remains in the sample, whereas the equimolar

Oxytocin induces mating behavior in rats of both sexes. Previous experiments revealed that progesteroneinduced sex behavior in ovariectomized, estrogen-primed rats was caused by release of NO from NOergic neurons that stimulated the release of luteinizing hormone-releasing hormone (LHRH). The LHRH activated brain-stem neurons that initiated the lordosis ref lex. We hypothesized that oxytocin might similarly release NO in the medial basal hypothalamic region that would stimulate release of LHRH into the hypophyseal portal vessels to release luteinizing hormone. To investigate this hypothesis, medial basal hypothalamic explants were preincubated in Krebs-Ringer bicarbonate buffer for 30 min, followed by a 30-min incubation in fresh Krebs-Ringer bicarbonate buffer containing the compounds to be tested. Oxytocin stimulated LHRH release 3-to 4-fold at the lowest concentration tested (10 ؊10 M). Values remained at a plateau as the concentration was increased to 10 ؊7 M and then declined in a concentration-dependent manner, so that there was no stimulation with a concentration of 10 ؊5 M. Oxytocin (10 ؊7 M) stimulated release of prostaglandin E 2 into the medium, a finding consistent with a role of NO in the response. That NO indeed mediated the action of oxytocin was supported by blockade of the action of oxytocin by the competitive inhibitor of NO synthase (NOS), N G -monomethyl-L-arginine (300 M). Furthermore, oxytocin (10 ؊9 to 10 ؊7 M) activated NOS as measured at the end of the experiments. Oxytocin appeared to act to stimulate norepinephrine terminals in the medial basal hypothalamus, which activated NOS by ␣ 1 -adrenergic receptors, because prazocine, an ␣ 1 receptor blocker, inhibited the LHRH-releasing action of oxytocin. Finally, incubation of neural lobe explants with sodium nitroprusside, a NO releasor, revealed that nitroprusside (300-600 M, but not 900 M) inhibited oxytocin release. Therefore, the NO released by oxytocin also diffuses into the oxytocin neuronal endings and inhibits oxytocin release, forming a negative feedback loop. The results indicate that oxytocin is important not only in induction of mating, but also in stimulating LHRH release with subsequent luteinizing hormone discharge that plays a crucial role in reproduction.Although oxytocin is one of the most abundant peptides in the body, little is known about its function. In the female, it is critical for milk ejection during lactation and plays an important role in parturition by inducing uterine contractions (1, 2). Oxytocin also appears to influence maternal and mating behavior, because intraventricular injection of the peptide induces these behaviors in female rats (3, 4).Although the amounts of oxytocin present in the neurohypophysis of male and female rats are similar, its function in the male has not been established (1). It induces natriuresis in both sexes (1), and recent evidence indicates that it may do so by releasing atrial natriuretic peptide (5).Intraventricular injection of oxytocin causes penile erection in male ra...

In infection bacterial products such as lipopolysaccharides (LPS) induce inducible nitric oxide synthase (iNOS) that produces large quantities of NO toxic to the invading organisms, but also often has toxic effects on host cells. Therefore, inhibition of iNOS activity might be beneficial in combatting these adverse effects. To determine if methylene blue (MB), an oxidizing agent that inactivates iNOS, would reduce the iNOS levels in the medial basal hypothalami (MBH) of conscious male rats, LPS (5 mg/kg) was injected intravenously (i.v.), and after 3 h they were injected i.v. with either MB (3 mg/kg) or saline and the effects on iNOS in the MBH determined. iNOS was measured by conversion of labeled arginine into citrulline by incubating MBH in the absence of calcium (Ca²⁺) since iNOS does not require Ca²⁺ for activation. The results indicate that iNOS was induced by the injection of saline, but the induction by LPS was much greater, an increase of 10-fold above that of control sham-operated animals. Both the induction of iNOS from the stress of saline injections and LPS were completely eliminated by MB indicating that MB might be beneficial in preventing injury to brain tissue following LPS injection. There was no effect of either LPS or MB on the Ca²⁺-dependent constitutive NOS activity.

It has previously been demonstrated that uterine nitric oxide synthase (NOS) activity increases before embryonic implantation in rats. The aim of the present work was to investigate the regulation and the physiological relevance of the nitric oxide (NO) system in ovoimplantation. The increase in NOS activity in early pregnancy was found to be independent of the presence of embryos in the uterus. Whereas the Ca2+-dependent isoform of NOS increased gradually in the preimplantation days, the Ca2+-independent isoform increased just at the beginning of implantation (Day 5, 1800 hours); then the activity of both isoforms declined. Oestradiol, whose concentration peaks before implantation, might be regulating NOS activity in the uterus, since treatment of rats with tamoxifen, a receptor antagonist, reduces the activity of both isoforms to preimplantation levels. Intraluminal injections of L-NAME (0.5 mg kg[-1]), a competitive inhibitor of NOS, reduced by 50% the number of implanted embryos; this suggests that the NO system plays a role during implantation. The data suggest that oestradiol might be a modulator of NOS activity during nidation and that NO production is necessary to achieve a successful embryo implantation.

In kidney, nitric oxide (NO) produced by nitric oxide synthase (NOS) regulates sodium and water excretion and renal medullary blood flow. However, excessive NO production causes nitrative damage and oxidative stress. Since oxidative stress may be linked to hypertension, we examined the expression and activity of inducible NOS (iNOS) in the kidney of the spontaneously hypertensive rat (SHR) and compared our findings to control normtotensive Wistar Kyoto (WKY) rat. Compared with WKY rat, there was significant (p < .05) overexpression (by 96%) and increased (2-fold) activity of iNOS in the cortex but not in the outer medulla, of SHR kidney; in the inner medulla, there was a 6.9-fold increase in iNOS activity in SHR. Increased expression (by 104%) and activity (3.3-fold) of iNOS was specifically observed in proximal tubules (PTs) of the cortex, accompanied by higher (2-fold) tissue nitrite levels. Although certain antioxidant enzymes such as catalase and Mn-superoxide dismutase were overexpressed, glutathione peroxidase was underexpressed in SHR PTs. Overexpression of the inducer of the iNOS promoter, nuclear factor-kappaB (NF-kappaB), with elevated nitrotyrosinylated proteins, further confirmed an elevated state of iNOS-induced oxidative stress in SHR kidneys, possibly signifying its role in the maintenance of essential hypertension seen in these animals.

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