Role of pre‐ and postjunctional inhibition by prostaglandin E 2 of lipolysis induced by sympathetic nerve stimulation in dog subcutaneous adipose tissue in situ

Summary1 Canine subcutaneous adipose tissue was isolated and autoperfused in situ after labelling of the noradrenaline stores by 3 H‐(—)‐noradrenaline. 2 Prostaglandin E 2 (10–200 ng/ml) increased blood flow and glucose uptake, and caused a dose‐dependent inhibition of lipolysis induced by sympathetic nerve stimulation (4 Hz). The actions of exogenous prostaglandin E 2 are therefore similar to those of prostaglandin E 1 in this tissue. There were no consistent effects of prostaglandin E 2 on the vasoconstriction or on the 3 H‐noradrenaline overflow induced by nerve stimulation. 3 Phenoxybenzamine (1·5–2 mg i.a.) caused a 5‐fold increase in 3 H‐noradrenaline overflow and a 95% reduction of the vasoconstrictor response to nerve stimulation. The lipolytic response was similar to that of the control. Prostaglandin E 2 (100–200 ng/ml) administered after phenoxybenzamine caused a 90% inhibition of lipolysis, while the vasoconstrictor response was enhanced to about 50% of control. Prostaglandin E 2 inhibited 3 H‐noradrenaline overflow by about 50% but it was still larger than that of the control. 4 It is suggested that exogenous prostaglandin E 2 inhibits lipolysis induced by sympathetic nerve stimulation mainly by a postjunctional action in canine subcutaneous adipose tissue.