STIMULATION CORTICOTROPIN-RELEASING HORMONE-RELEASE BY THE OBESE (OB)GENE-PRODUCT, LEPTIN, FROM HYPOTHALAMIC EXPLANTS

RECENT data have suggested that adipocytes synthesize and secrete a 16 kDa peptide which acts centrally to regulate weight gain by suppressi ng appetite and activating the sympathetic nervous system. To exert su ch effects, it may function as an endogenous ligand in the CNS, since specific receptors (OB-R) have been recently reported to be widely dis tributed in the brain. We have speculated that this peptide, now known as leptin, may act centrally by stimulating the release of corticotro phin-releasing hormone (CRH), a recognized potent inhibitory modulator of appetite. We tested in vitro the effect of murine leptin on CRH se cretion in the dose range of 0.1 pM-100 nM. The static rat hypothalami c incubation system used involved fresh hypothalamic explants maintain ed in EBSS with consecutive 20 min incubations, and estimation of CRH concentrations in the medium by a specific and sensitive radioimmunoas say. The effect of heat-denatured leptin at a dose of 1 nM and 10 nM, was also investigated. Any possible modulation of leptin effects by ad renergic pathways was then explored by coincubating hypothalami with l eptin 10 nM and equimolar concentrations of the alpha(1)-adrenergic an tagonist prazosin or the beta-adrenergic antagonist propranolol. The a ctive leptin, but not the heat-inactivated peptide, caused a dose-depe ndent stimulation of CRH release in vitro (p < 0.05 - < 0.0001 us cont rol), with a plateau effect at a dose of 10 nM. The addition of either prazosin or propranolol was without effect on leptin-dependent CRH st imulation. These findings are consistent with the reported presence of leptin receptors in the rat brain, and suggest that leptin may act to regulate appetite at least in part by directly modulating the secreti on of CRH from the hypothalamus. It would also appear that such effect occurs via a nonadrenergic mechanism.