Effects of morphine on isoenzymes of pyruvate kinase and tyrosine aminotransferase in rat

Abstract

The acute and chronic effects of morphine on isoenzymes of pyruvate kinase and tyrosine aminotransferase in rat liver have been studied in vivo. Acute administration of morphine inhibits the L-type pyruvate kinase but increases forms II, III and IV of tyrosine aminotransferase in rats which have received a single intraperitoneal injection of morphine 6 hr prior to sacrifice. However both effects are lost after 24 hr. Morphine starts to regain its stimulatory effect on tyrosine aminotransferase at the hr 48 and reaches a maximum at the hr 72. Chronic morphinization leads to similar changes in the total activities of pyruvate kinase and tyrosine aminotransferase but the change in isoenzyme pattern of tyrosine aminotransferase concerns only forms II and III. Results from this study support the hydrocortisone-like property of morphine and indicate that morphine may enhance gluconeogenesis in vivo.