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.