title: Progressive weakening of the response of key enzymes of liver glycogen metabolism to permanently increased plasma epinephrine levels.
abstract: In adult male rats anaesthetized with pentobarbital the intravenous infusion of 0.5 micrograms.kg-1.min-1 of epinephrine increased liver phosphorylase a activity within 5 min, whereas later a weakening of the hormone effect was observed. After increasing the infusion rate to 1.0 micrograms.kg-1.min-1 and extending the study to more parameters, the diminishing effect on phosphorylase was confirmed and a similar response was established for liver cAMP. Concomitantly, a decrease and recovery of liver glycogen synthase a activity was observed. In rats with permanent catheters in one of their tail arteries for obtaining blood samples, the plasma epinephrine levels were shown to be permanently increased (from cca 1 pmol.ml-1 before infusion of 1.0 micrograms.kg-1.min-1 to more than 30 pmol.ml-1 during infusion) and remained at steady levels throughout the infusion. Therefore, the weakening of the epinephrine effect should be ascribed to changes at (or beyond) the catecholamine receptor level. A hitherto undescribed decrease of total glycogen synthase activity was observed during the infusions.
authors.affiliation: Institute of Experimental Endocrinology, Slovak Academy of Sciences, Bratislava.
authors.forename: S
authors.initials: S
authors.lastname: Németh
authors.forename: E
authors.initials: E
authors.lastname: Viskupic
authors.forename: R
authors.initials: R
authors.lastname: Kvetnanský
authors.forename: J
authors.initials: J
authors.lastname: Kolena
mesh_terms: D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism; D004837:Epinephrine / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D006006:Glycogen Synthase / Q000378:metabolism*; D007262:Infusions, Intravenous; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008112:Liver Glycogen / Q000378:metabolism*; D008297:Male; D010762:Phosphorylase a / Q000378:metabolism*; D006005:Phosphorylases / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D008112:Liver Glycogen; D000242:Cyclic AMP; D010762:Phosphorylase a; D006005:Phosphorylases; D006006:Glycogen Synthase; D004837:Epinephrine