A neuronal nitric oxide synthase inhibitor 7-nitroindazole reduces the 5-HT1A receptor against 8-OH-DPAT-elicited hyperphagia in rats

Zymosan and lipopolysaccharide decrease gene expression of neuronal nitric oxide synthase in peripheral organs in chicks

Nitric oxide (NO) is gaseous bioactive molecule that is synthesized by NO synthase (NOS). Inducible NOS (iNOS) expression occurs in response to pathogenic challenges, resulting in the production of large amounts of NO. However, there is a lack of knowledge regarding neuronal NOS (nNOS) and endothelial NOS (eNOS) in birds during pathogenic challenge. Therefore, the present study was conducted to determine the influence of intraperitoneal (IP) injection of zymosan (cell wall component of yeast) and lipopolysaccharide (LPS, a cell wall component of gram-negative bacteria) on NOS expression in chicks (Gallus gallus). Furthermore, the effect of NOS inhibitors on the corresponding behavioral and physiological parameters was investigated. Zymosan and LPS injections induced iNOS mRNA expression in several organs. Zymosan had no effect on eNOS mRNA expression in the organs investigated, whereas LPS increased its expression in the pancreas. Zymosan and LPS decreased nNOS mRNA expression in the lung, heart, kidney, and pancreas. The decreased nNOS mRNA expression in pancreas was probably associated with the NO from iNOS provided that such effect was reproduced by IP injection of sodium nitroprusside, which is a NO donor. Furthermore, pancreatic nNOS mRNA expression decreased following subcutaneous injection of corticosterone. Furthermore, IP injections of a nonspecific NOS inhibitor, NG-nitro-L-arginine methyl ester, and an nNOS-specific inhibitor, 7-nitroindazole, resulted in the significant decreases in food intake, cloacal temperature, and feed passage via the digestive tract in chicks. Collectively, the current findings imply the decreased nNOS expression because of fungal and bacterial infections, which affects food intake, body temperature, and the digestive function in birds.

Inhibition of nitric oxide synthase or cystathionine gamma-lyase abolishes leptin-induced fever in male rats

Leptin is an adipokine that regulates energy balance and immune function. Peripheral leptin administration elicits prostaglandin E₂-dependent fever in rats. The gasotransmitters nitric oxide (NO) and hydrogen sulfide (H₂S) are also involved in lipopolysaccharide (LPS)-induced fever response. However, there is no data in the literature indicating if these gasotransmitters have a role in leptin-induced fever response. Here, we investigate the inhibition of NO and H₂S enzymes neuronal nitric oxide synthase (nNOS), inducible nitric oxide synthase (iNOS), and cystathionine γ-lyase (CSE) in leptin-induced fever response, respectively. Selective nNOS inhibitor 7-nitroindazole (7-NI), selective iNOS inhibitor aminoguanidine (AG), and CSE inhibitor dl-propargylglycine (PAG) were administered intraperitoneally (ip). Body temperature (Tb), food intake, and body mass were recorded in fasted male rats. Leptin (0.5 mg/kg ip) induced a significant increase in Tb, whereas AG (50 mg/kg ip), 7-NI (10 mg/kg ip), or PAG (50 mg/kg ip) caused no changes in Tb. AG, 7-NI, or PAG abolished leptin increase in Tb. Our results highlight the potential involvement of iNOS, nNOS, and CSE in leptin-induced febrile response without affecting anorexic response to leptin in fasted male rats 24 h after leptin injection. Interestingly, all the inhibitors alone had the same anorexic effect induced by leptin. These findings have implications for understanding the role of NO and H₂S in leptin-induced febrile response.

Iron Regulation of Pancreatic Beta-Cell Functions and Oxidative Stress

Dietary advice is the cornerstone in first-line treatment of metabolic diseases. Nutritional interventions directed at these clinical conditions mainly aim to (a) improve insulin resistance by reducing energy-dense macronutrient intake to obtain weight loss and (b) reduce fluctuations in insulin secretion through avoidance of rapidly absorbable carbohydrates. However, even in the majority of motivated patients selected for clinical trials, massive efforts using this approach have failed to achieve lasting efficacy. Less attention has been given to the role of micronutrients in metabolic diseases. Here, we review the evidence that highlights (a) the importance of iron in pancreatic beta-cell function and dysfunction in diabetes and (b) the integrative pathophysiological effects of tissue iron levels in the interactions among the beta cell, gut microbiome, hypothalamus, innate and adaptive immune systems, and insulin-sensitive tissues. We propose that clinical trials are warranted to clarify the impact of dietary or pharmacological iron reduction on the development of metabolic disorders.

Regulation of obesity and insulin resistance by nitric oxide

Obesity is a risk factor for developing type 2 diabetes and cardiovascular disease and has quickly become a worldwide pandemic with few tangible and safe treatment options. Although it is generally accepted that the primary cause of obesity is energy imbalance, i.e., the calories consumed are greater than are utilized, understanding how caloric balance is regulated has proven a challenge. Many "distal" causes of obesity, such as the structural environment, occupation, and social influences, are exceedingly difficult to change or manipulate. Hence, molecular processes and pathways more proximal to the origins of obesity-those that directly regulate energy metabolism or caloric intake-seem to be more feasible targets for therapy. In particular, nitric oxide (NO) is emerging as a central regulator of energy metabolism and body composition. NO bioavailability is decreased in animal models of diet-induced obesity and in obese and insulin-resistant patients, and increasing NO output has remarkable effects on obesity and insulin resistance. This review discusses the role of NO in regulating adiposity and insulin sensitivity and places its modes of action into context with the known causes and consequences of metabolic disease.

Inducible-NOS but not neuronal-NOS participate in the acute effect of TNF-α on hypothalamic insulin-dependent inhibition of food intake

TNF-alpha acts on the hypothalamus modulating food intake and energy expenditure through mechanisms incompletely elucidated. Here, we explore the hypothesis that, to modulate insulin-induced anorexigenic signaling in hypothalamus, TNF-alpha requires the synthesis of NO. TNF-alpha activates signal transduction through JNK and p38 in hypothalamus, peaking at 10(-8) M. This is accompanied by the induction of expression of the inducible and neuronal forms of NOS, in both cases peaking at 10(-12) M. In addition, TNF-alpha stimulates NOS catalytic activity. Pre-treatment with TNF-alpha at a low dose (10(-12) M) inhibits insulin-dependent anorexigenic signaling, and this effect is abolished in iNOS but not in nNOS knockout mice.

Melatonin enhances NADPH-diaphorase activities in the hypothalamus of maternally-separated rats

Maternal separation or social isolation is a risk factor in the development of mammalian species affecting both physical and mental growth, and food intake regulation. Melatonin has been known to regulate body weight on various species including rodents. We investigated the effect of melatonin treatment on the expression of nitric oxide synthase, which may involved in food intake regulation, in the brain of maternally separated-rats using nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry. Melatonin (10 mg/kg i.p.) was injected to 14-day-old maternally-separated rats for 7 days. Maternally-separated rats with melatonin administration showed significantly higher staining intensities of NADPH-d-positive neurons in the paraventricular nucleus (PVN) and in lateral hypothalamic area (LHA) than maternally-separated without melatonin administration (P < 0.05). Body weight of melatonin treated rats significantly increased at the 6th and 7th day compared to that of rats without melatonin treatment (P < 0.05). These results indicate that melatonin may be associated with increase body weight via NOS in the hypothalamic areas in maternally-separated or socially isolated rats.

Central administration of a nitric oxide precursor abolishes both the hypothalamic serotonin release and the hypophagia induced by interleukin-1beta in obese Zucker rats

Serotonin-induced anorexia has long been recognized as an important part of the CNS mechanisms controlling energy balance. More recently, interleukin-1beta and nitric oxide have been suggested to influence this control, possibly through modulation of hypothalamic serotonin. The present work aimed at investigating the interaction of these systems. We addressed whether 5-HT is affected during IL-1beta-induced anorexia in obese Zucker rats and the influence of the central NO system on this IL-1beta/5-HT interaction. Using microdialysis, we observed that an intracerebroventricular injection of 10 ng IL-1beta significantly stimulated 5-HT extracellular levels in the VMH, with a peak variation of 102+/-41% above baseline. IL-1beta also significantly reduced the 4-h feeding by 33% and the 24-h feeding by 42%. Contrarily, these effects were absent when IL-1beta was injected 2 h after the i.c.v. administration of 20 microg of the NO precursor L-arginine. The results suggest that, in obese Zucker rats, activation of the serotonergic system in the medial hypothalamus participates in IL-1beta-induced anorexia. Since L-arginine, probably through NO stimulation, abolished both the anorexia and the serotonergic activation, it can be proposed that the NO system, either directly or indirectly, counteracts IL-1beta anorexia. The hypothalamic serotonergic system is likely to mediate this NO effect.

Effects of long-term inhibition of neuronal nitric oxide synthase (NOS1) in uninephrectomized diabetic rats

Nitric oxide (NO) has been implicated in the pathogenesis of renal hemodynamic changes in diabetes mellitus (DM). However, the role of NO in the pathophysiology of diabetic nephropathy remains controversial. Renal hemodynamic changes in experimental DM can be acutely normalized by selective inhibition of neuronal NO synthase (nNOS). This observation suggests a nephroprotective potential of nNOS inhibition in DM. To explore this issue we assessed the long-term effects (12 weeks) of selective nNOS inhibition with the specific inhibitor S-methyl-L-thiocitrulline (SMTC) in uninephrectomized control and streptozotocin-diabetic rats. No beneficial effects of SMTC were observed in nondiabetic controls. In contrast, SMTC delayed the development of proteinuria (32+/-8 vs. 53+/-9 mg/24h, week 8, p < 0.05) and glomerulosclerosis (GS, 0.30+/-0.08 vs. 0.57+/-0.05, p < 0.05) in diabetic rats. These effects coincided with early effects of treatment on the glomerular filtration rate, and were associated with lower renal expression of nNOS. Furthermore, SMTC-treated diabetic rats demonstrated reduced weight gain and urinary sodium excretion as compared to vehicle-treated counterparts, despite similar metabolic control and blood pressure. In summary, long-term nNOS inhibition had modest nephroprotective effects in uninephrectomized diabetic rats. These effects may be mediated by renal hemodynamic mechanisms, as well as by lower food (protein) intake.

A nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester, attenuates lipoprivic feeding in mice

Possible involvement of nitric oxide (NO) in lipoprivic feeding was investigated in nondeprived male ICR mice adapted to a high-fat diet in a within-subjects design. Lipoprivation was induced by blocking fatty acid oxidation with Na-mercaptoacetate (MA), which produces a short-term increase in feeding in mice and rats. Food intake, measured at 1, 2, and 4 h following injection of 70 mg/kg of MA, was attenuated in a dose related manner with increasing pretreatment dose (1,10, 25 and 50 mg/kg sc) of the NO-synthase (NOS) inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), reaching statistical significance at 10 mg/kg of L-NAME at h1 when compared to vehicle control condition. The inactive isomer, D-NAME, was ineffective, thereby supporting stereospecific drug action and directly implicating NO. A control experiment measured general locomotor activity (grid crossings and rears) in an open arena under 10-50 mg/kg of L-NAME in the same mice; both measures were significantly different from vehicle condition only at the highest dose. These findings support involvement of NO in lipoprivic hyperphagia; they are consistent with and extend research linking NO and ingestive behaviors through use of NOS inhibitors. Possible influences of confounds were discussed.

Multiplicity of mechanisms of serotonin receptor signal transduction

The serotonin (5-hydroxytryptamine, 5-HT) receptors have been divided into 7 subfamilies by convention, 6 of which include 13 different genes for G-protein-coupled receptors. Those subfamilies have been characterized by overlapping pharmacological properties, amino acid sequences, gene organization, and second messenger coupling pathways. Post-genomic modifications, such as alternative mRNA splicing or mRNA editing, creates at least 20 more G-protein-coupled 5-HT receptors, such that there are at least 30 distinct 5-HT receptors that signal through G-proteins. This review will focus on what is known about the signaling linkages of the G-protein-linked 5-HT receptors, and will highlight some fascinating new insights into 5-HT receptor signaling.

Differential expression of nicotinamide adenine dinucleotide phosphate-diaphorase in hypothalamic areas of obese Zucker rats

Several studies have suggested that the activity of nitric oxide synthase (NOS) may be involved in the regulation of food intake in the genetically obese Zucker rats. In the present study, we investigated the expression of NOS in various hypothalamic regions of obese and lean Zucker rats using nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry. Obese Zucker rats showed significantly lower staining intensities of NADPH-diaphorase-positive neurons in the paraventricular nucleus (PVN), lateral hypothalamic area (LHA) and ventromedial hypothalamic nucleus (VMH) than lean Zucker rats did. The differences in staining intensities between obese and lean Zucker rats were large in both the PVN and LHA, but such differences were relatively small in the VMH.

A nitric oxide synthase inhibitor reduces hyperphagia induced in rats by the 5-HT(1A) receptor agonist, 8-OH-DPAT, independently of hypothalamic serotonin metabolism

In rats, a nitric oxide (NO) synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME) inhibited the hyperphagia induced by the 5-hydroxytryptamine (5-HT)(1A) autoreceptor agonist, 8-hydroxy-2-di-n-(propylamino)tetralin (8-OH-DPAT). 8-OH-DPAT reduced 5-HT metabolism in the hypothalamus, and this was not blocked by pretreatment with L-NAME. L-NAME also did not affect basal hypothalamic 5-HT metabolism or reverse the decreases in 5-HT synthesis in hypothalamus. These results suggest that the hypophagic effects of L-NAME, which inhibits NO formation, are independent of 5-HT metabolism in the hypothalamus.