Differential signaling pathway on antilipolytic action of insulin in sheep and rat adipocytes

Isoproterenol statistically increased a dose-dependent manner in glycerol release and cAMP production in ovine and rat adipocytes. Isoproterenol-stimulated lipolysis was significantly inhibited by treatment of insulin. LY294002, a specific inhibitor of PI3-kinase, significantly blocked the anti-lipolytic effect of insulin on dose-dependent manners in both adipocytes. Unlike insulin, PDGF, which stimulates PI3-kinase activity located in the plasma membrane, did not show the inhibition of antilipolysis in, ovine and rat adipocytes. When the cells were treated with PD098059, a specific MEK inhibitor, insulin-stimulated antilipolysis was not affected in rat adipocytes, while it was partially inhibited in sheep. These results suggest that PI3-kinase cascade is major pathway on insulin-induced antilipolysis in both adipocytes, however, insulin exerts MAPK-dependent effects in sheep, not rat adipocytes.