Pancreatic Hormones and Hepatic Methionine Adenosyltransferase in the Rat

Abstract

SummaryOur previous finding that hepatic methionine adenosyltransferase varies directly with the level of glucocorticoids prompted the investigation of this enzyme in the catabolic conditions associated with insulin deficiency and during the administration of excess glucagon. While glucagon administration had little effect, alloxan diabetes caused a marked elevation of the transferase level in rat liver. Combined treatment with alloxan and a glucocorticoid showed an additive effect. The influence of alloxan diabetes on this enzyme was independent of hyperglycemia. The response to alloxan diabetes could be prevented and reversed by either insulin administration or adrenalectomy. The effect of glucocorticoids on enhancing methionine adenosyltransferase activity in diabetic rats was also prevented by insulin. However, the administration of insulin to normal rats caused a slight but consistent increase, rather than decrease, in the basal level of the enzyme. The increase in the transferase activity in the livers of alloxan-treated rats was largely blocked by actinomycin D or cycloheximide, indicating the synthesis of new RNA and protein is associated with the response of this enzyme to alloxan diabetes.