Effects of insulin on amino acid release and urea formation in perfused rat liver

Abstract

Inhibitory effects of insulin on the accumulation of perfusate amino and urea nitrogen were studied in isolated livers of nonfasted rats, cyclically perfused in situ. In experiments lasting up to 3 hr. the continuous delivery of insulin at 0.8 [mu]g (20 milliunits)/hr. reduced maximally the increases in both amino and urea nitrogen, and concentrations of all perfusate amino acids that could be assessed chromatographically were lowered. The net inhibitory effect of insulin under these conditions was equivalent in nitrogen to 1.4 mg protein/g liver per hr. Addition of a complete amino acid mixture evoked a rapid uptake of amino acids and enhancement of urea formation, but did not alter the net increase in amino + urea nitrogen or the effect of insulin on it. Although the incorporation of leucine-I-C14 and valine-I-C14 into protein was increased slightly in the presence of insulin, the effects were equivocal and the hormonal reduction in nitrogen release was felt to be consistent with inhibition of protein degradation.