Epinepherine Inhibits the Activity of Phosphatidate Phosphohydrolase of Isolated Human Hepatocytes

ABSTRACT

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 micro M, reaching a maximum inhibition of 64.5% at 100 micro concentration. Inclusion of alprenolol, a Beta- receptor blocker, in the incubation mixture abolished the inhibitory effect of epinephrine on PAP, whereas the alpha-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 inhibitism 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 beta- adrenoceptor activation and cAMP is involved in the mechanism by which PAP activity is altered