EPINEPHRINE INHIBITS THE A CTIVITY OF PHOSPH ATIDATE PHOSPHOHYDROLASE OF ISOLATED HUMA N HEPATOCYTES

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 µM, reaching a maximum inhibition of 64.5% at 100 µM concentration. Inclusion of alprenolol, a β-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 β-adrenoceptor activation and cAMP is involved in the mechanism by which PAP activity is altered.