Centrally administered muring leptin stimulates plasma arginine-vasopressin secretion and increases the level of mRNA expression in the supraoptic nucleus of conscious rats

The product of the ob gene protein, leptin, has been suggested to function as an endogenous mediator of the cardiovascular system via sympathetic nerv e activity. Moreover, extensive distribution of leptin receptor-like immuor eactivity has been demonstrated in the choroid plexus, cerebral cortex, hip pocampus, thalamus and hypothalamus, especially in the paraventricular nucl eus (PVN) and supraoptic nucleus (SON). In this study, we have investigated the in vivo effects of leptin on plasma arginine-vasopressin (AVP) secreti on and the level of AVP messenger ribonucleotic acid (AVP mRNA) in the SON of conscious rats. Intracerebroventricularly administered leptin increased plasma AVP concentration in a dose-dependent manner (0-400 pmol/rat). The m aximal effect was obtained at 15 min after the administration of leptin. Fu rthermore, in Northern blot analyses, the levels of AVP mRNa in the SON inc reased approximately 2-fold from the basal level after the administration o f leptin. AVP mRNA expression in the PVN was also increased by leptin. Howe ver, leptin had no effects on plasma oxytocin (OXT) secretion and OXT gene expression in the SON. In conclusion, leptin is involved in AVP secretion v ia the central nervous system, however, its physiological role is unknown.