Effect of morphine on gluconeogenesis and ureogenesis in rat liver

The stimulation of glycogenolysis and gluconeogenesis in isolated hepatocytes by opioid peptides

The opioid agonists [leucine]enkephalin, [D-Ala2,D-Leu5]enkephalin and dynorphin-(1-13)-peptide, but not morphine, stimulated the conversion of [2-14C]pyruvate into glucose and glycogenolysis when added directly to isolated hepatocytes. Naloxone produced a small but significant inhibition of both the basal and stimulated rate of incorporation of label into glucose but had no effect on the total glucose output by the cells. The effects of the opioid peptides were mediated by a cyclic AMP-independent mechanism.

Influence of morphinization on the development of isoenzymes of pyruvate kinase in rat liver

1. Acute administration or morphine to foetuses and neonates either directly or via the mother leads to a decrease in the total pyruvate kinase activity. 2. The L-type isoenzyme is selectively suppressed while the M-type isoenzyme is not altered to any significant extent with a consequent lowering of the L/M ratio. 3. The decrease in the total pyruvate kinase activity and the L/M ratio is more prominent when the route of administration of morphine is via the mother. 4. The possible explanation for this difference in the route of administration is that morphine can be converted into a more active metabolite with greater biological potency in adult animals.