Prostaglandins, alpha-adrenergic receptors and lipolysis in hamster fat cells.

In hamster fat cells, PGE2, PGI1 and clonidine (alpha 2-adrenoceptor agonist) were shown to inhibit markedly lipolysis stimulated by methylisobutylxanthine (MIX) (2 X 10(-4) M) and slightly that provoked by isoprenaline (5 X 10(-7) M). The similar inhibitory actions of the alpha 2-adrenoceptor agonist clonidine and PGE2 on lipolysis stimulated by MIX led us to examine possible reversal of the antilipolytic effect of PGE2 by yohimbine (alpha 2-adrenoceptor antagonist). However, the absence of an effect of yohimbine on PGE2, antilipolytic action indicated that the PGE2 receptor was different from the alpha 2-adrenoceptor of hamster fat cells. In these studies, PGE2 was shown to be a more potent antilipolytic agent that PGI2 (IC50 values 2 X 10(-9) and greater than 10(-4) M respectively).