Role of adenosine in insulin-stimulated release of leptin from isolated white adipocytes of Wistar rats

Leptin, the ob gene product that; can decrease caloric intake and increase energy expenditure, is functionally released by insulin from adipose tissue . Adenosine is thought to be an important regulator of the action of insuli n in adipose tissue. The present study investigated the role of adenosine i n the release of leptin by insulin in isolated rat white adipocytes. Releas e of leptin, measured by radioimmunoassay, from insulin-stimulated samples was seen after 30 min. Adenosine deaminase, at concentrations sufficient to metabolize endogenous adenosine, decreased insulin-stimulated leptin relea se. Also, the insulin-stimulated leptin release was completely blocked by t he adenosine A(1) receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (D PCPX). Mediation of endogenous adenosine in this action of insulin was furt her supported by the assay of adenosine released into the medium from adipo cytes stimulated with insulin. In addition, activation of adenosine A(1) re ceptors by N-6-cyclopentyladenosine (CPA) induced an increase in leptin rel ease in a concentration-dependent manner that could be blocked by antagonis ts, either DPCPX or 8-(p-sulfophenyl)theophylline (8-SPT). In the presence of U73312, a specific inhibitor of phospholipase C (PLC), CPA-stimulated le ptin secretion from adipocytes was reduced in a concentration-dependent man ner, but it was not affected by U73343, the negative control for U73312. Mo reover, chelerythrine and GF 109203X diminished the CPA-stimulated leptin s ecretion at concentrations sufficient to inhibit protein kinase C (PKC). Th ese results suggest that, in isolated white adipocytes, the released adenos ine acts as a helper and/or a positive regulator for insulin in the release of leptin via an activation of adenosine A, receptors that involves the PL C-PKC pathway.