Modulation of vascular tone and glycerol levels measured by in situ microdialysis in rat adipose tissue

Changes in blood flow induced by the beta-adrenoceptor agonist isoproterenol(Iso) and a stable analogue of the major metabolite of arachidonic acid in adipose tissue, carbaprostacyclin (cPGI(2)), have been studied in rat periepididymal fat pad with in situ microdialysis by measuring the distribution ratio of 0.2% ethanol in the dialysate (outflow) to that in the perfusate (inflow) (O/I ratio). Local perfusions of 1 mu M cPGI(2) or 1 mu M Iso led to reversible decreases of the O/I ratio that were similar to the decrease induced by the vasodilating reference drug hydralazine (Hydra, 630 mu M) Interestingly, a continuous perfusion of Hydra at a submaximal vasodilating concentration (63 mu M) was sufficient to prevent further vasodilatation induced by Iso or cPGI(2). To take advantage of this observation, experiments were designed to evaluate the influence of the vasodilating effect of Iso or cPGI(2) on the ability of either to induce lipolysis in vivo. The results showed that the vasodilating effect of Iso could contribute to glycerol removal from the extracellular fluid and demonstrated that cPGI(2) was devoid of lipolytic activity.