THE EFFECTS OF GLUCAGON, INSULIN AND S TEROID HORMONES ON PHOSPHATIDATE PHOSPHOHYDROLASE ACTIVITY IN RAT LIVERS

The effects of steroid hormones, glucagon and insulin on rat liver phosphatidate phosphohydrolase (PAP) activity were studied both in vitro and in vivo. Incubation of rat hepatocytes with each hormone showed that dehydroepiandrosterone (DHEA), progesterone and testosterone increase PAP activity by 44.6, 37 and 36.9%, respectively. Estradiol, however, decreased enzyme activity by 13.6% under the same conditions. Similar results were obtained when these hormones were injected in rats, in which PAP activity increased by DHEA (19.7%), testosterone (17%) and progesterone (88%) and decreased by estradiol (38.8%). Incubation of the hepatocytes with insulin however, did not change PAP activity significantly even at 144 J.LM concentrations, whereas glucagon progressively stimulated the enzyme activity, reaching 7 1% at 50 J.LM concentration under the same conditions. In rats injected with glucagon, PAP activity also rose up to 79% after 30 min, after which time it declined but remained above the control level at 45 min. The data imply the role of PAP activity in the mechanism by which androgens and progesterone increase serum triacylglycerols and decrease serum HDL-c and their possible regulation by these hormones.