CONTRASTING EFFECTS OF PHORBOL DIBUTYRATE AND PHORBOL-MYRISTATE ACETATE IN RABBIT AORTA

In rat hepatocytes, active phorbol esters inhibited the alpha1-adrenergic stimulation of phosphatidylinositol labeling with the expected potency order: phorbol myristate acetate (PMA) > phorbol dibutyrate (PDB). In contrast, in rabbit aorta the alpha1-adrenergic action was inhibited dose-dependently by PDB but not by PMA. Similarly PDB (but not PMA) induced a strong contraction in rabbit aorta. The phorbol ester-induced contraction developed slowly, was dose-dependent and independent of extracellular calcium. These effects of PDB in rabbit aorta were neither inhibited by the protein kinase inhibitor H-7 nor mimicked by the synthetic diacylglycerol, OAG. Our results raise some doubts on the mechanism(s) through which the actions of PDB take place in rabbit aorta. © 1990.