Abstract

In this study both hydrocortisone and insulin were shown to increase the uptake of a nonmetabolizable amino acid, α-aminoisobutyric acid (AIB), by the isolated perfused rat liver. DNA-dependent RNA synthesis was inhibited by actinomycin D to determine whether the effects of these hormones on transport were independent of their actions on the transcription of genetic information. Actinomycin D inhibited enzyme induction by hydrocortisone approximately 90% without affecting the increase in AIB transport. However, approximately half of the insulin effect on AIB transport was blocked by actinomycin D. The effect of hydrocortisone on the uptake of AIB was completely inhibited by phenoxybenzamine (PBZ), an adrenergic blocking agent. The action of insulin on AIB uptake was not affected by PBZ. Hydrocortisone and insulin together exerted an additive effect on the hepatic uptake of AIB. Both hormones act directly (but apparently at different sites) to increase the AIB uptake by the liver. Most of the steroid action and approximately half of the insulin action appears to be independent of any effect these hormones have on DNA-dependent RNA synthesis in the liver.