Inhibitory effect of alpha-melanocyte stimulating hormone through melanocortin 4 receptor on iNOS expression in the hypothalamus of male rats.

C. CARUSO; C. MOHN; V. RETTORI; H. WATANOBE; H. SCHIOTH; G. JAITA; A. SEILICOVICH; M. LASAGA

Philadelphia, USA

Congreso; The Endocrine Society's 85th annual meeting; 2003

The Endocrine Society

There is evidence that alpha-melanocyte stimulating hormone (a-MSH) has a number of immunomodulatory and anti-inflammatory actions probably due to inhibition of the induction of nitric oxide (NO) by lipopolysaccharide (LPS) and/or pro-inflammatory cytokines. On the other hand, melanocortin MC3 and MC4 receptors were found in the hypothalamus. Therefore we investigated the effect of a-MSH and HS024 (a specific MC4 antagonist) injected to freely moving rats into lateral cerebral ventricle (icv) through a cannula (implanted stereotaxically a week before the experiment) on inducible and neuronal NO synthase (iNOS and nNOS) expression (assayed by RT-PCR) in the mediobasal hypothalamus (MBH) in control and LPS- treated male Wistar rats. After 3 h, LPS (250 ug/rat, ip) induced iNOS expression in the hypothalamus. This stimulatory effect was reduced by 70-80% with the icv administration of a-MSH (5 ug/rat), injected 30 min before LPS administration. a-MSH alone was without effect. The administration of HS024 for 3 h 30 min (1nmol/rat, icv) also induced an increase in iNOS expression. The combination of both, HS024 icv and LPS ip evoked a remarkable increase by 35-40 fold in iNOS expression in MBH. Neither LPS nor a-MSH nor HS024 alone or in combination produced any modifications in nNOS expression. We also examined the in vitro effect of cytokines on iNOS and nNOS mRNA levels and the effect of a-MSH. MBH were incubated for 5 hours in the presence of LPS (10 ug/ml), LPS+ Interferon gamma (IFN gamma) (100 ng/ml) and LPS+ Tumor necrosis factor (TNF-a) (50 ng/ml). LPS alone did not produce modifications in iNOS expression whereas LPS + IFN gamma and IFN gamma + TNF-a significantly increased iNOS mRNA levels by 3-4 fold and 4-5 fold respectively. The stimulatory effect of the cytokines was attenuated in the presence of a-MSH (1 and 5 uM) which by itself had no effect. There was no effect of the cytokines nor a-MSH on nNOS expression in MBH. The results show that a-MSH is able to block the increase in iNOS induction at the hypothalamic level due to endotoxemia. Also it is possible that endogenous a-MSH may exert an inhibitory tone on the induction of iNOS via MC4 receptors