Studies on gluconeogenesis, protein synthesis and cyclic AMP levels in isolated parenchymal cells following insulin withdrawal from alloxan diabetic rats

Abstract

Alloxan diabetic rats maintained on protamine zinc insulin for two weeks were used for these studies. Isolated liver cells were prepared from these rats at various time intervals after the withdrawal of insulin (0, 48, 72, and 96 hr). A maximal increase in the rate of gluconeogenesis in the presence of 10mM alanine (14–34 fold), lactate (4–7 fold), pyruvate (4–6 fold), or fructose (2–3 fold) is observed in isolated diabetic liver cells 72 hr after the withdrawal of insulin from the donor rat. Protein synthesis in isolated diabetic liver cells as measured by the incorporation of radioactive isoleucine, valine and phenylalanine into protein decreases (5–6 fold) with time after insulin withdrawal. Glucagon (10 −6M) alone increases cyclic AMP levels five-fold, while glucagon with theophylline (1mM) increases cyclic AMP levels ten-fold in liver cells isolated from rats maintained on insulin (0 hr) or from rats withdrawn from insulin for 48 hr. The ability of glucagon to elevate cyclic AMP levels in isolated diabetic liver cells decreases at 72 hr following insulin withdrawal.