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Articles in PresS, published online ahead of print March 6, 2002
Am J Physiol Cell Physiol, 10.1152/ajpcell.00033.2002
Submitted on January 22, 2002
Accepted on February 27, 2002
1 Physiology, Laval University, Quebec, Quebec, Canada
* To whom correspondence should be addressed. E-mail: ludwik.bukowiecki{at}phs.ulaval.ca.
The mechanisms regulating leptin secretion were investigated in isolated rat white adipocytes. Insulin (1-100 nM) linearly stimulated leptin secretion from incubated adipocytes for at least 2 h. The adrenergic agonists norepinephrine, isoproterenol (two non-selective ß-agonists) or CL 316243 (potent ß3) all inhibited insulin (10 nM)-stimulated leptin release. The inhibitory effects of norepinephrine and isoproterenol could be reversed, not only by the non-selective antagonist propranolol, but also by the selective antagonists ICI 89406 (ß1) or ICI 118551 (ß2), the ß2-antagonist being less effective than the ß1. Insulin-stimulated leptin secretion could also be inhibited by a series of agents increasing intracellular cAMP levels such as lipolytic hormones (ACTH, TSH), various nonhydrolysable cAMP analogues, pertussis toxin, forskolin, methylxanthines (caffeine, theophylline, IBMX) and specific inhibitors of phosphodiesterase III (imazodan, milrinone and amrinone). Significantly, antilipolytic agents other than insulin (adenosine, nicotinic acid, Acipimox, orthovanadate) acid did not mimic the acute stimulatory effects of insulin on leptin secretion under these conditions. We conclude that norepinephrine specifically inhibits insulin-stimulated leptin secretion not only via the low affinity ß3-adrenoceptors, but also via the high affinity ß1/ß2-adrenoceptors. Moreover, it is suggested that: (1) activation of phosphodiesterase III by insulin represents an important metabolic step in stimulation of leptin secretion, and (2) lipolytic hormones competitively counter-regulate the stimulatory effects of insulin by activating the adenylate cyclase system.
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