title: The stimulation of glycogenolysis in isolated hepatocytes by opioid peptides.
abstract: The opioid peptides [Leu]enkephalin and dynorphin-(1-13) were shown to enhance glycogen breakdown when added directly to hepatocytes. This was the result of a concerted effect on the enzymes of glycogen metabolism, with a stimulation of glycogen phosphorylase activity and a simultaneous decrease in glycogen synthase I activity. The latter only became significant when the enzyme was activated by incubating the cells in presence of 20 mM- or 40 mM-glucose. The effect of the opioid peptides was independent of an increase in cyclic AMP or any change in the activity ratio of the cyclic AMP-dependent protein kinase and was abolished by depleting the cells of Ca2+. Both [Leu]enkephalin and dynorphin-(1-13) produced a significant decrease in cyclic AMP formation, suggesting that in liver, as in neuronal tissue, they may act by inhibiting adenylate cyclase activity.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004399:Dynorphins / Q000494:pharmacology*; D004743:Enkephalin, Leucine / Q000494:pharmacology*; D006006:Glycogen Synthase / Q000378:metabolism; D066298:In Vitro Techniques; D008099:Liver / Q000187:drug effects / Q000201:enzymology; D008112:Liver Glycogen / Q000378:metabolism*; D008297:Male; D010762:Phosphorylase a / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013268:Stimulation, Chemical
chemical_list: D008112:Liver Glycogen; D004743:Enkephalin, Leucine; D004399:Dynorphins; D000242:Cyclic AMP; D010762:Phosphorylase a; D006006:Glycogen Synthase; D011494:Protein Kinases; D002118:Calcium