Nitric oxide synthase inhibitors enhance plasma levels of corticosterone and ACTH

Normal responses to restraint stress in mice lacking the gene for neuronal nitric oxide synthase

The hormonal changes associated with immobilization stress (IMO) include a swift increase in corticosterone (CORT) concentration and a decrease in circulating testosterone (T) levels. There is evidence that the production of the short-lived neuromodulator nitric oxide (NO) is increased during stress in various tissues, including the brain. NO also suppresses the biosynthesis of T. Both the inducible and the neuronal isoforms of NO synthase (iNOS and nNOS, respectively) have been implicated in this suppression, but the evidence has not been conclusive. We used adult wild-type (WT) and nNOS knockout male mice (nNOS-/-) to assess the respective roles of CORT and nNOS-derived NO in stress mediated inhibition of T production. Animals were assigned to either basal control or 3-hour IMO groups. No difference in basal plasma and testicular T levels were observed between WT and nNOS-/-, although testicular weights of mutant mice were slightly lower compared to WT animals. The plasma contents of luteinizing hormone (LH) and CORT in unstressed mice of both genotypes were similar. Exposure to 3 hours of IMO increased plasma CORT and decreased T concentrations in mice of both genotypes. However, comparable levels of plasma LH and testicular nitrite and nitrate (NOx), NO stable metabolites, were detected in control and stressed WT and nNOS-/- mice. Adrenal concentrations of NOx declined after IMO, but the reduction was not statistically significant. These findings implicate CORT rather than NO generated by nNOS in the rapid stress-induced suppression of circulating T.

Neuronal nitric oxide synthase gene inactivation reduces the expression of vasopressin in the hypothalamic paraventricular nucleus and of catecholamine biosynthetic enzymes in the adrenal gland of the mouse

The impact of a lifelong absence of the neuronal nitric oxide synthase (nNOS) in the neuroendocrine stress response was investigated in nNOS knockout (KO) and wild type (WT) mice under basal conditions and in response to forced swimming. In the hypothalamic paraventricular nucleus oxytocin and corticotropin-releasing-hormone mRNA levels did not differ between these genotypes under resting conditions, whereas vasopressin mRNA levels were significantly lower in nNOS KO than in WT animals. Also, in the adrenal glands basal levels of tyrosine hydroxylase protein, the rate-limiting enzyme for catecholamine biosynthesis, and of phenylethanolamine N-methyltransferase, which converts norepinephrine to epinephrine, were significantly reduced in nNOS KO mice. Plasma adrenocorticotropin, corticosterone, norepinephrine and epinephrine levels were similar in the KO and WT genotypes under resting conditions. In response to forced swimming, a similar increase in plasma adrenocorticotropin and corticosterone was observed in KO and WT animals. Stressor exposure triggered also an increased epinephrine release in WT animals, but did not significantly alter plasma epinephrine levels in KO mice. These data suggest that the chronic absence of nNOS reduces the capacity of epinephrine synthesising enzymes in the adrenal gland to respond to acute stressor exposure with an adequate epinephrine release.

Altered Regulation of Type II 11β-hydroxysteroid Dehydrogenase in the Kidney of Rats with Experimental Hypertension

The present study was aimed at investigating the role of type II 11β-hydroxysteroid dehydrogenase (IIβ-HSD II) in the development of hypertension. Two-kidney, one-clip (2K1C), deoxycorticosterone acetate (DOCA)/salt, or N^G-nitro-L-arginine methyl ester (L-NAME) hypertension was induced in male Sprague-Dawley rats. Four weeks later, the expression of 11β-HSD II mRNA was determined in the kidney by Northern blot analysis. The plasma level of aldosterone was measured by radioimmunoassay. In 2K1C hypertension, the expression of 11β-HSD II was decreased in the clipped kidney and increased in the non-clipped kidney. The expression was increased in the remnant kidney of DOCA/salt hypertension, while decreased in the kidneys of L-NAME hypertension. The plasma level of aldosterone was increased, decreased, and remained unchanged in 2K1C, DOCA/salt, and L-NAME hypertension, respectively. The down-regulation of 11β-HSD II may contribute to the sodium retention, thereby increasing the blood pressure in 2K1C and L-NAME hypertension. On the contrary, the up-regulation in DOCA/salt hypertension may play a compensatory role to dissipate the sodium retention.

Prenatal corticosterone exposure results in altered AT1/AT2, nephron deficit and hypertension in the rat offspring

Maternal treatment with the synthetic glucocorticoid, dexamethasone has been reported to result in a nephron deficit and development of hypertension in the offspring of rats. However, it is not known whether elevated maternal corticosterone (CORT), the natural glucocorticoid, has similar effects on blood pressure and nephron endowment. The present study investigated the effects of CORT (0.8 mg kg(-1) day(-1)) administration on embryonic day 14 (E14) and E15 of pregnancy on: (1) nephron number at postnatal day 30 (PN30); (2) blood pressure at PN120; and (3) receptors of the renal renin-angiotensin system (RRAS) (AT(1)Ra, AT(1)Rb and AT(2)Ra) during both embryonic (E16, E20) and adolescent (PN30) life. Plasma CORT concentrations were approximately doubled 30 min after injection. Unbiased stereological analysis revealed that maternal CORT treatment resulted in a nephron deficit of 21 and 19% in male and female offspring, respectively. Mean arterial pressures were significantly elevated in offspring of both sexes from the CORT group. Real-time PCR revealed that CORT treatment increased expression of AT(1)Ra and AT(2)R at E16, and at PN30. Expression of AT(1)Rb was downregulated in embryonic life but upregulated at PN30. We believe that these results are the first to demonstrate that maternal CORT treatment results in a nephron deficit and development of hypertension in the rat offspring. Changes in the RRAS may be contributing to these phenotypes. Critically, this study suggests that increased but physiological levels of the natural glucocorticoid can programme similar changes to those seen with pharmacological doses of the synthetic glucocorticoid. This may have important implications for women experiencing significant stress during pregnancy.

Testosterone production in mice lacking inducible nitric oxide synthase expression is sensitive to restraint stress

Immobilization stress (IMO) induces a rapid increase in glucocorticoid secretion [in rodents, corticosterone CORT)] and this is associated with decreased circulating testosterone (T) levels. Nitric oxide (NO), a reactive free radical and neurotransmitter, has been reported to be produced at higher rates in tissues such as brain during stress. The biosynthesis of T is also known to be dramatically suppressed by NO. Specifically, the inducible isoform of nitric oxide synthase (iNOS) was directly implicated in this suppression. To assess the respective roles of CORT and NO in stress-mediated inhibition of T production, adult wild-type (WT) and inducible nitric oxide synthase knockout (iNOS(-/-)) male mice were evaluated. Animals of each genotype were assigned to either basal control or 3-h IMO groups. Basal plasma and testicular T levels were equivalent in both genotypes, whereas testicular weights of mutant mice were significantly higher compared with WT animals. Exposure to 3-h IMO increased plasma CORT and decreased T concentrations in mice of both genotypes. Testicular T levels were also affected by stress in WT and mutant males, being sharply reduced in both genotypes. However, the concentrations of nitrite and nitrate, the stable metabolites of NO measured in testicular extracts, did not differ between control and stressed WT and iNOS(-/-) mice. These results support the hypothesis that CORT, but not NO, is a plausible candidate to mediate rapid stress-induced suppression of Leydig cell steroidogenesis.

Nitric oxide impairs baroreflex gain during acute psychological stress

Psychological stress can suppress baroreflex function, but the mechanism has not been fully elucidated. Nitric oxide in the brain and in the adrenal cortex, as well as plasma glucocorticoids, increases during stress and has been shown to suppress reflex gain in unstressed animals. Therefore, the purpose of this study was to test the hypothesis that stress, caused by exposure to a novel environment, decreases baroreflex gain in rabbits through the actions of nitric oxide to increase corticosterone release. Baroreflex control of heart rate and plasma corticosterone levels was quantified before and after blockade of nitric oxide synthase (NOS) with N(omega)-nitro-L-arginine (L-NNA; 20 mg/kg iv) in conscious rabbits exposed to a novel environment and in the same rabbits once they had been conditioned to the environment. Stress significantly reduced baroreflex gain from -23.4 +/- 2 to -12.2 +/- 1.6 beats x min(-1) x mmHg(-1) (P < 0.05) and increased plasma corticosterone levels from 5.4 +/- 0.7 to 15.5 +/- 5.0 ng/ml (P < 0.05). NOS blockade increased gain in stressed animals (to -27.2 +/- 5.4 beats x min(-1) x mmHg(-1), P < 0.05) but did not alter gain in unstressed rabbits (-26.8 +/- 4.9 beats x min(-1) x mmHg(-1)) such that gain was equalized between the two states. NOS blockade increased plasma corticosterone levels in unstressed animals (to 14.3 +/- 2.1 ng/ml, P < 0.05) but failed to significantly alter levels in stressed rabbits (14.0 +/- 3.9 ng/ml). In conclusion, psychological stress may act via nitric oxide, independently of increases in corticosterone, to decrease baroreflex gain.

Endotoxin administration increases hypothalamic somatostatin mRNA through nitric oxide release

Acute inflammation induced by endotoxin (LPS) administration inhibits insulin-like growth factor (IGF-I) and growth hormone (GH) secretion. The aim of this study was to elucidate the role of glucocorticoids and nitric oxide (NO) in the effect of LPS on hypothalamic somatostatin gene expression. Adult male Wistar rats were injected with different doses of LPS (5, 10 and 100 microg/kg). Rats received two i.p. injections of LPS (at 17:30 and 8:30 h the following day) and were killed 4 h after the second injection. LPS administration at the dose of 100 microg/kg increased the hypothalamic somatostatin mRNA content, as well as the serum concentrations of corticosterone. Glucocorticoids do not seem to be involved in LPS-induced increase in hypothalamic somatostatin mRNA since adrenalectomy did not prevent this effect. In order to analyze the possible effect of NO, aminoguanidine, an inducible nitric oxide synthase inhibitor, was injected (100 mg/kg s.c.) simultaneously with LPS injection. Aminoguanidine administration did not modify somatostatin mRNA in saline injected rats, but it prevented LPS-induced increase in hypothalamic somatostatin mRNA. These data suggest that the stimulatory effect of endotoxin on hypothalamic somatostatin gene expression is not mediated by glucocorticoids, but instead by the increase in NO release.

Aluminum-induced suppression of testosterone through nitric oxide production in male mice

Excessive nitric oxide (NO) production in mice serum and testis due to aluminum (Al) exposure has been shown in previous studies. The aim of this study was to further investigate the role of NO on aluminum-suppressed testosterone level in male CD-1 mice. Each animal in six groups, was given intraperitoneal injections of either saline, aluminum chloride (AlCl(3)), l-N(6)-(1-iminoethyl) lysine (NO synthase inhibitor, l-NIL), or Al chloride along with l-NIL for a period of 12 days. These groups were denoted as C (control, saline), AL (35mg Al/kg/day, saline), NIL240 (total 240mg l-NIL/kg, saline), ALNIL240 (35mg Al/kg/day, total 240mg l-NIL/kg), ALNIL60 (35mg Al/kg/day, total 60mg l-NIL/kg), and NIL60 (total 60mg l-NIL/kg, saline). Results indicated that serum/testicular aluminum levels increased significantly in aluminum-treated animals compared to the controls, whereas the values observed from groups ALNIL240 than AL/ALNIL60 were markedly lower. Aluminum administration significantly increased NO production and decreased both testicular adenosine 3',5'-cyclic monophosphate (cAMP) and testosterone levels. A lower level of NO and higher concentrations of cAMP and testosterone observed in the ALNIL240 group indicated that the protective effect of NO synthase blockage was significant, although incomplete. In addition, aluminum induction significantly elevated the testicular cholesterol, but the values were lower in the ALNIL240 group than the AL or the ALNIL60 group. Finally, it was suggested that aluminum compounds exerted a significant adverse effects on the steroidogenesis and cAMP, which aided in the transport of cholesterol to the inner mitochondrial membrane. Furthermore, nitric oxide synthase blockage prevented aluminum-induced reproductive toxicity.

Nω-nitro-l-arginine methyl ester attenuates lithium-induced c-Fos, but not conditioned taste aversion, in rats

Lithium chloride (LiCl) at doses sufficient to induce conditioned taste aversion (CTA) causes c-Fos expression in the relevant brain regions and activates the hypothalamic-pituitary-adrenal (HPA) axis. It has been suggested that nitric oxide (NO) in the central nervous system may play a role not only in the activation of HPA axis but also in CTA learning, and that LiCl may activate the brain NO system. To determine the role of NO in lithium-induced CTA, we examined the lithium-induced CTA, brain c-Fos expression, and plasma corticosterone level with Nomega-nitro-L-arginine methyl ester (L-NAME) pretreatment. Intraperitoneal L-NAME (30 mg/kg) given 30 min prior to LiCl significantly decreased lithium-induced c-Fos expression in the brain regions implicated in CTA learning, such as the hypothalamic paraventricular nucleus (PVN), central nucleus of amygdala (CeA), and nucleus tractus of solitarius. However, either the lithium-induced CTA acquisition or the increase in plasma corticosterone was not attenuated by l-NAME pretreatment. These results suggest that NO may be involved in lithium-induced neuronal activation of the brain regions, but not in the CTA acquisition or the HPA axis activation.

Nitric oxide potently inhibits the rate-limiting enzymatic step in steroidogenesis

This study tested the hypothesis that nitric oxide (NO) inhibits the rate-limiting catalytic step in steroidogenesis, cytochrome P450 cholesterol side-chain cleaving enzyme (CYP11A1), independent of soluble guanylyl cyclase (GC-S) stimulation. To assess CYP11A1 activity, pregnenolone levels were quantified in murine adrenocortical Y1 cells in the presence of the 3beta-hydroxy-Delta(5)-steroid dehydrogenase inhibitor, 2alpha-cyano-17beta-hydroxy-4,4',17alpha-trimethylandrost-5-ene-3-one. The NO donor, (Z)-1-[2-(2-aminoethyl-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate(deta nonoate), inhibited vasoactive intestinal peptide-, forskolin- and 22alpha-hydroxycholesterol (22HC)-facilitated pregnenolonogenesis in the absence of GC-S activation and in the presence of a GC-S inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). CYP11A1 was also heterologously expressed in monkey COS7 cells. Deta nonoate inhibited 22HC-facilitated activity of the over-expressed enzyme in the absence of GC-S activation and in the presence of ODQ. The NO-independent, GC-S agonist, 1-benzyl-3-(5'-hydroxymethyl-2'-furyl)indazole did not inhibit steroidogenesis. The IC(50) for effects of free NO on CYP11A1 was potent and in the 0.4-2 microM range. These results support the hypothesis that NO inhibits the rate-limiting enzyme in steroidogenesis independent of GC-S activation.

Lack of neuronal NOS has consequences for the expression of POMC and POMC-derived peptides in the mouse pituitary

The relevance of NO in neuroendocrine signalling has been investigated by analysis of cellular expression of pro-opiomelanocortin (POMC) and the POMC-derived peptides beta-endorphin, alpha-melanocyte stimulating hormone and adrenocorticotropin. Expression patterns were studied in the pituitary gland of 150-day old wild-type and neuronal-NOS (nNOS) knock-out mice by using immunohistochemistry, in situ hybridization and Northern blot analysis. Remaining NO-generating capacities in the knock-out mice were demonstrated by immunohistochemical localization of inducible, endothelial and neuronal NOS isoforms. Quantitative analysis revealed that cellular expression of POMC mRNA was drastically reduced in the pituitary of knock-out mice in comparison to controls. In situ hybridization studies demonstrated that this reduction was most pronounced in the intermediate lobe, while the anterior lobe was much less affected. Immunostaining for the proteolytic fragments of POMC was significantly reduced in the intermediate lobe cells of knock-out mice. A moderate reduction of immunostaining for these peptides was also observed in adenopituitary cells of nNOS knock-out mice. Our data demonstrate that the lack of nNOS substantially affects cellular levels of pituitary opioid peptides, which may have consequences for the response of these animals to stress and pain.

Local inhibition of nitric oxide temporarily stimulates aldosterone secretion in conscious sheep in vivo

The effect of localized blockage of endogenous nitric oxide (NO) on basal aldosterone secretion was studied in conscious sheep with autotransplanted adrenal glands. We have shown that infusion of the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME; 130 microg/l blood flow) significantly stimulated basal aldosterone secretion rate (ASR). This stimulatory effect was seen up to 4 h of infusion. Beyond this time point, however, the elevated ASR level was not sustained, and it was seen to drop markedly to lower than control values at 5 h. L-NAME had no effect on cortisol secretion rate (FSR) during the first 4 h of infusion, but a significant reduction in FSR was seen by the 8-h time point. Adrenal blood flow was consistently decreased in association with long L-NAME infusion. Additionally, L-NAME was shown to have no effect on aldosterone secretion when infused systemically. We conclude that the relationship between NO and aldosterone secretion is an inhibitory one, in which NO seems to have a negative effect on basal aldosterone secretion.

Endothelial cell nitric oxide inhibits aldosterone synthesis in zona glomerulosa cells: modulation by oxygen

The regulation of aldosterone synthesis by endogenous nitric oxide (NO) was examined in cultured cells of the adrenal cortex. Endothelial NO synthase (eNOS) was detected by Western blot in cultured adrenal endothelial cells (ECs) but not in zona glomerulosa (ZG) cells or adrenal fibroblasts. Neither inducible (iNOS) nor neuronal NOS (nNOS) isoforms were detected in the cells. Only ECs had NOS activity and converted [(3)H]L-arginine to [(3)H]L-citrulline. Angiotensin II (ANG II, 100 nM) increased EC production of nitrate/nitrite by 2.4-fold. Coincubation with ECs or treatment with DETA nonoate increased the fluorescence of ZG cells loaded with an NO-sensitive dye, diaminofluorescein 2 diacetate (DAF-2 DA). DETA nonoate inhibited ANG II (1 nM) and potassium (10 mM) -stimulated aldosterone release in a concentration-related manner. This inhibitory effect of NO was enhanced >10-fold by decreasing the oxygen concentration from 21 to 8%. Coincubation of EC and ZG cells in 8% oxygen inhibited ANG II-induced aldosterone release, and inhibition was reversed by blockade of NOS. These findings indicate that adrenal EC-derived NO inhibits aldosterone release by cultured ZG cells and that the sensitivity to NO inhibition is increased at low oxygen concentrations.

Is steroid deficiency the cause of tolerance in nitrate therapy?

The award of the Nobel Prize in Physiology and Medicine for 1998 bears witness to the 'explosive' field of nitric oxide (NO), and who would have thought the explosive nitroglycerin owed its therapeutic effectiveness to this little molecule? NO is also involved in causing penile erection, which has brought sildenafil to the aid of patients with erectile dysfunction. However, emerging evidence in animals and in vitro studies indicates that NO also inhibits steroidogenesis, which may have repercussions in humans. The decrease in androgen secretion may impact on secondary sexual characteristics, including penile size. The tolerance to the nitrate therapy in angina, characterized by volume expansion and not due to sodium retention, may also be related to steroid hormone deficiency. Decreased cortisol secretion may impair water excretion, resulting in volume expansion. Impaired aldosterone secretion would cause hyponatraemia with resultant raised renin. I hypothesize that continuous therapy with nitrates and sildenafil will result in diminished levels of steroid hormones with predicted sequelae.

Endogenous nitric oxide suppresses rat myometrial connexin 43 gap junction protein expression during pregnancy

Nitric oxide (NO) synthase (NOS) is active in the gravid uterus, and its activity decreases prior to the onset of parturition. We tested the hypothesis that NO helps maintain uterine quiescence by suppressing the expression of genes necessary for parturition. Pregnant rats (18 days gestation) were treated with inducible NOS (iNOS) inhibitor N-iminoethyl-L-lysine (NIL) or endothelial NOS inhibitor nitro-L-arginine methyl ester (L-NAME); 24 h later, uteri were analyzed for myometrial connexin 43 (Cx43) protein by immunoblotting and mRNA by Northern analysis. Myometrial oxytocin receptors (OTR) were measured by radioligand binding, and decidual prostaglandin H synthase (PGHS) protein by immunoblotting. Uterine NOS blockade was verified by NOS activity assay. We found that NIL, but not L-NAME, significantly increased myometrial Cx43 protein to parturitional levels with treatment at 19 but not 17 days gestation. Steady state mRNA concentrations were not changed at 24 h. NOS inhibition did not increase the concentrations of OTR, or PGHS protein, nor did it decrease maternal serum progesterone. We conclude that endogenous uterine NO from iNOS suppresses myometrial Cx43 gap junction protein expression during rat pregnancy. Although the exact mechanism is unknown, an increase of uterine wall stretch due to inhibition of relaxation could account for increased Cx43 gene transcription.

Endothelin-1 and blood pressure after inhibition of nitric oxide synthesis in human septic shock

BACKGROUND

The systemic hypotension during human sepsis has been ascribed to increased production of nitric oxide (NO). Therefore, inhibitors of NO synthesis have been used in the treatment of hypotension in patients with septic shock. In addition, NO production may inhibit the synthesis and vasoconstrictor effects of endothelin-1 (ET-1). In this study, we tested whether ET-1 contributed to the vasopressor action of the NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) in patients with severe septic shock.

METHODS AND RESULTS

Compared with healthy volunteers, patients with septic shock had increased plasma levels of nitrite/nitrate (37+/-5 [SEM] versus 12+/-5 mmol/L, P<0.01), the stable end products of NO metabolism, and ET-1 (45+/-7 versus 3+/-2 pg/mL, P<0.001). Plasma ET-1 concentration was not related to plasma nitrite/nitrate concentration or blood pressure. Continuous infusion of L-NAME (1 mg. kg-1. h-1 IV) for 12 hours increased mean arterial pressure by 43+/-5% and systemic vascular resistance by 64+/-10% (both P<0.01). The increase in blood pressure and systemic vascular resistance correlated positively with the level of ET-1 (both P<0. 005) but not with plasma nitrite/nitrate level. L-NAME infusion did not result in significant changes in the plasma concentrations of ET-1 or nitrite/nitrate.

CONCLUSIONS

NO and ET-1 may both play a role in the cardiovascular derangements of human sepsis. Although L-NAME does not increase ET-1 concentration in patients with septic shock, the vasopressor response induced by L-NAME depends on the plasma level of ET-1. These findings may indicate that inhibitors of NO synthesis unmask a tonic pressor response of ET-1 in human septic shock.

Nitric oxide and biopterin in depression and stress

Depression has been hypothesized to be related to the reduced biosynthesis of neurotransmitters such as serotonin, noradrenalin and dopamine. Much past research has also been devoted to dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis in depression. The present article reviews the evidence linking tetrahydrobiopterin, a co-factor in the biosynthesis of neurotransmitters, and nitric oxide, an apparent neuroendocrine modulator of the HPA axis, to the immune system and to neuronal control within affective disorder and stress. On the basis of this review, it is suggested that future psychoneuroimmunological research should more fully explore the possible role of tetrahydrobiopterin and nitric oxide in depressive disorders.

Regulation of nitric oxide synthase messenger RNA expression in the rat hippocampus by glucocorticoids

Nitric oxide and glucocorticoids have been implicated in learning and memory, as well as in regulation of the stress response. By use of the in situ hybridization technique, we examined the role of glucocorticoids in the regulation of nitric oxide synthase messenger RNA in the hippocampus. In control animals, nitric oxide synthase subtype I (neuronal) messenger RNA was expressed in the CA1, CA3 and dentate gyrus of the hippocampus. Nitric oxide synthase subtype I expression was almost absent in CA2 pyramidal neurons. Neither subtype II (immunological) nor subtype III (endothelial) nitric oxide synthase messenger RNAs were observed in neurons of the hippocampal subfields. Bilateral removal of the adrenal glands resulted in a significant increase in nitric oxide synthase subtype I messenger RNA expression in the CA1 and CA3 pyramidal neurons and in granular cells of the dentate gyrus. To a lesser degree, the nitric oxide synthase subtype I messenger RNA signal was increased in CA2 pyramidal neurons. Daily administration of glucocorticoids for one week attenuated the adrenalectomy-induced increased level of expression of the messenger RNA encoding nitric oxide synthase subtype I in all areas studied. Because adrenalectomy, which suppresses the production of glucocorticoids, increases nitric oxide synthase expression, and replacement of adrenalectomized animals with glucocorticoids restores the basal levels of nitric oxide synthase subtype I expression, our results demonstrate an up-regulation of nitric oxide synthase subtype I messenger RNA in the absence of glucocorticoids in the hippocampus. The present findings suggest an involvement of the stress axis in the regulation of the synaptic plasticity process mediated by nitric oxide in the hippocampus.

Nitric oxide is a potential down-regulating molecule in autoimmune disease: inhibition of nitric oxide production renders PVG rats highly susceptible to EAE

Rat strains vary in their susceptibility to experimental autoimmune encephalomyelitis (EAE) and in many cases, factors other than MHC antigens are thought to play a role in this. We found that PVG rats, which have a very low susceptibility to EAE, were rendered highly susceptible to clinical disease when treated with N-methylarginine (NMA) an inhibitor of nitric oxide synthase (NOS). The clinical course of the ensuing disease in NMA-treated PVG rats was in most cases fulminating in nature and accompanied by some mortality. Following immunisation with myelin basic protein (MBP)-complete Freund's adjuvant (CFA), PVG rats developed higher serum levels of the surrogate markers of nitric oxide production, reactive nitrogen intermediates (RNI; nitrite and nitrate), than did their Lewis counterparts. This in vivo finding was reflected in vitro, where the levels of RNI produced in 24, 48 and 72 h IFN-gamma-stimulated spleen cell cultures for PVG rats were significantly higher than those for Lewis rats. A mechanism by which increased NO production might protect PVG rats against clinical EAE was suggested by the finding that lymph node cells, isolated from NMA-treated MBP-immunised PVG rats, proliferated in response to MBP at a rate approximately 3 x greater than those from MBP-immunised, saline treated rats. Thus, the greater number of MBP-specific T cells generated in the NOS inhibitor-treated vs. untreated rats could account for their increased susceptibility to developing clinical EAE. The findings in this study suggest that NO plays a role in protecting PVG rats against developing EAE.

The involvement of nitric oxide in stress-impaired testicular steroidogenesis

The participation of the nitric oxide (NO) pathway in downregulation of testicular steroidogenesis in normal and stressed rats was investigated both in vivo and in vitro. In Leydig cells from normal animals, isosorbide dinitrate, an NO donor, decreased the human chorionic gonadotropin (CG)-stimulated and progesterone-derived androgen production. Also, the intratesticular injection of a precursor of NO, arginine (10 mg/testis), transiently decreased serum androgen levels and inhibited human CG-stimulated androgen production in acute testicular cultures. These effects were eliminated in rats cotreated with Nomega-nitro-L-arginine methyl ester (L-NAME) (2 X 600 microg/each testis). Acute immobilization stress (2 h) decreased serum androgen levels and inhibited human CG-stimulated androgen production in vitro. These effects were accompanied by a significant increase in nitrite, a stable oxidation product of NO, in testicular cultures. Bilateral intratesticular injection of L-NAME prevented the stress-induced decrease of human CG-stimulated androgen production, and significantly reduced the nitrite levels. These results implicate NO in normal and stress-impaired testicular steroidogenesis.

Reduced cartilage proteoglycan loss during zymosan-induced gonarthritis in NOS2-deficient mice and in anti-interleukin-1-treated wild-type mice with unabated joint inflammation

OBJECTIVE

To investigate the role of nitric oxide (NO) and interleukin-1 in (IL-1) joint inflammation and cartilage destruction during zymosan-induced gonarthritis (ZIA).

METHODS

Monarticular arthritis was elicited by intraarticular injection of zymosan. The effect of NO deficiency on arthritis was studied in mice with genetically disrupted NOS2. The role of IL-1 was examined by treating wild-type mice with neutralizing anti-murine IL-1(alpha+beta) antibodies. Joint swelling was measured externally by the increased uptake of circulating 99mtechnetium pertechnetate. Proteoglycan (PG) synthesis was assessed using 35S-sulfate incorporation into patellae ex vivo. Histology evaluated exudation and infiltration of leukocytes and the extent of cartilage destruction.

RESULTS

The proinflammatory mediators NO, IL-1, and IL-6 were released by the articular tissues during the first hours of inflammation. Interestingly, anti-IL-1 treatment moderately reduced, and NOS2 deficiency moderately enhanced, joint swelling. However, the influx of neutrophils into the joint occurred independently of IL-1 and NOS2 activities. In the first week of inflammation, chondrocyte PG synthesis was significantly suppressed and chondrocytes became unresponsive to their essential anabolic factor, insulin-like growth factor 1 (IGF-1). Anti-IL-1 treatment or NOS2 deficiency prevented the inhibition of PG synthesis, and the chondrocytes remained IGF-1 responsive. Intraarticular injections of IL-1alpha into NOS2-deficient mice did not affect PG synthesis, thus proving that NO mediated this IL-1 effect in vivo. Furthermore, histology showed that cartilage PG loss was markedly ameliorated in NOS2-deficient and anti-IL-1-treated mice. Intermediate cartilage pathology was found in mice that were heterozygous for disrupted NOS2.

CONCLUSION

IL-1 and NO play a minor role in edema and neutrophil influx, but a major role in cartilage destruction of ZIA. In this model of murine arthritis, cartilage destruction was, for the most part, caused by pronounced suppression of PG synthesis and IGF-1 unresponsiveness of the chondrocytes, which were induced by de novo-synthesized IL-1 and were mediated by NOS2 activation.