Medical Journal of the Islamic Republic of Iran EPINEPHRINE INHIBITS THE A CTIVITY OF PHOSPH ATIDATE PHOSPHOHYDROLASE OF

The effect of epinephrine on phosphatidate phosphohydrolase (PAP) activity of isolated human hepatocytes was studied. Epineprine inhibited the enzyme activity progressively at concentrations above 0.1 �, reaching a maximum inhibition of 64.5 % at 100 � concentration. Inclusion of alprenolol, a �receptor blocker, in the incubation mixture abolished the inhibitory effect of epinephrine on PAP, whereas the (i-receptor antagonist phentolamine, or agonist phenylephrine, did not significantly change the hormone's effect. Addition of dibutyryl-cAMP or.aminophylline (a cAMP phosphodiesterase inhibitor) to the incubation mixture together with epinephrine caused further enzyme inhibiti.on reaching 65.6 % and 63.7%, respectively, compared to 49 % inhibition caused by epinephrine alone under the same conditions. Dibutyryl-cAMP alone also inhibited PAP activity (51 %). The results suggested that epinephrine affects human hepatocyte PAP activity through �adrenoceptor activation and cAMP is involved in the mechanism by which PAP activity is altered