CB1- and CB2-cannabinoid receptor-independent lipolysis induced by WIN 55,212-2 in male rat adipocytes

The expression of genes encoding the cannabinoid CB1 and CB2 receptors and fatty acid amide hydrolase (FAAH) and the lipolytic activity of cannabinoid agonists were investigated in rat adipose tissue. RT-PCR studies indicated that the genes encoding CB1 and CB2 receptors and FAAH are not expressed in epididymal adipocytes. In functional studies, the non-selective cannabinoid receptor agonist WIN 55,212-2 concentration-dependently (0.01-30 muM) induced glycerol release above baseline (E-max 96.1+/-6.2% of isoprenaline-induced lipolytic response). The selective CB2 agonist JWH-015 (0.01-30 muM) had no lipolytic activity while the endocannabinoid 2-arachidonoylglycerol and the stable anandamide derivative, R(+)-methanandamide had, only a weak lipolytic effect at the highest concentrations employed (10 and 30 muM). The concentration/response relationship for WIN 55,212-2-mediated lipolytic activity, mimicked by the S(-)-enantiomer WIN 55,212-3, was shifted significantly to the right by the CB1 antagonist AM 251 only at 10 muM, but was not modified by the beta-adrenoceptor antagonist propranolol (1 muM). The protein kinase inhibitor H-89, but not the two adenylyl cyclase inhibitors (+/-)N-6-R-phenylisopropyladenosine (R-PIA, 1 muM, a selective A(1) adenosine receptor agonist) or SQ 22,536 (50 muM) significantly reduced the glycerol efflux induced by WIN 55,212-2. Our data suggest that the cannabinoid drug WIN 55,212-2 may exert lipolytic activity in male rat adipocytes via an intracellular mechanism, not activated by CB1 or CB2 receptor stimulation, significantly reversed by H-89 but not clearly linked to stimulation of adenylyl cyclase.