Beta-3 agonist-induced lipolysis and nitric oxide production: relationship to PPARgamma agonist/antagonist and AMP kinase modulation

PPARgamma receptor agonist - troglitazone increases insulin sensitivity in visceral adipocytes and also increases fat mass. Beta-3 adrenergic receptor agonists mediate lipolysis and NO production (iNOS transcription) in visceral adipocytes. Troglitazone could possibly interfere with Beta-3-triggered lipolysis. We tested the crosstalk between PPARgamma agonist and Beta-3 agonist pathways on lipolysis and NO production in first 24 hours of treatment. Isolated epididymal rat adipocytes were cultivated in DMEM for 24 hours with treatment with Beta-3 agonist - BRL-37344, PPARgamma agonist - troglitazone, PPARgamma antagonist - SR-202 and AMPK blocker - compound C alone as well as in combinations. After 24 hours, lipolysis was measured by free glycerol, NO production by Griess reagent and iNOS mRNA by qRT-PCR. BRL-37344 increased lipolysis and NO production with iNOS transcription. Troglitazone increased all the three parameters as well but less than BRL-37344. Combination of troglitazone or SR-202 with BRL-37344 decreased NO production, iNOS transcription and lipolysis triggered before adding of BRL-37344. Compound C completely blocked the effect of troglitazone (and SR-202 as well) on BRL-37344. PPARgamma agonist/antagonist interferes with Beta-3 agonist activity in 24 hours. Troglitazone/SR-202 effect on Beta-3 triggered lipolysis and iNOS mRNA production is probably not PPAR gamma- but rather AMPK-dependent in first 24 hours (AMPK blocker - compound C blocked the effect).