Intracellular mechanisms involved in leptin regulation of sympathetic outflow.

Leptin acts in the hypothalamus to decrease appetite and increase sympathetic nerve activity. The leptin receptor is known to signal through the janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway to modulate transcription of target genes. Alteration of the activity of phosphoinositol-3 kinase (PI3K) by leptin has also been reported, and inhibition of PI3K is known to block the leptin-induced suppression of feeding. We tested the hypothesis that leptin-induced renal sympathetic nerve activation is mediated by PI3K. We evaluated renal sympathetic nerve activity (RSNA) and feeding responses of C57BL/6J mice to intracerebroventricular (ICV) administration of leptin in the presence or absence of selective inhibitors of PI3K (LY294002 or wortmannin). As expected, ICV administration of leptin decreased food intake at 4 hours and 24 hours and increased RSNA. Pretreatment with the PI3K inhibitor LY294002 markedly attenuated both the decrease in food intake and the increase in RSNA induced by leptin. Wortmannin also inhibited the RSNA response to leptin. In contrast, PI3K inhibitors did not affect the RSNA response to MTII (melanocortin-3/4 receptor agonist). Our data demonstrate that PI3K appears to play an important role in the transduction of leptin-induced changes in renal sympathetic outflow.