Age-dependent effects of phorbol ester on adenylate cyclase stimulation by glucagon in liver of female rats.
The stimulation of adenylate cyclase by glucagon and isoproterenol in cell lysates of hepatocytes isolated from fetal and adult female rats were measured after pretreatment with 12-O-tetradecanoyl-phorbol-13-acetate (TPA). Glucagon stimulation of adenylate cyclase activation was found to decrease in the hepatocyte lysate of adult female rats. Application of guanyl-5'-yl-imidodiphosphate (GppNHp) and forskolin showed this effect to be localized on the receptor level. However, glucagon stimulation of glucose liberation from phorbol ester-treated hepatocytes from adult female rats was not influenced. Maximum effects of glucose liberation were observed at glucagon concentrations which did not stimulate adenylate cyclase. The results are in agreement with the proposed existence of a low and high affinity glucagon receptor coupled to two different transducing systems. It is concluded that TPA uncouples in the liver of adult female rats--most likely by phosphorylation--the low affinity receptor from the adenylate cyclase system, whereas the high affinity receptor and phospholipase C/inositol 1,4,5-trisphosphate (IP3)/diacylglycerol (DAG) signalling systems do not seem to be affected. Such TPA effects could not be found in the liver of fetal rats.
Hermsdorf
T
T
Institute of Biochemistry, Karl-Marx University, Leipzig, GDR.
Dettmer
D
D
Hofmann
E
E
D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D005260:Female; D005333:Fetus; D005934:Glucagon / Q000494:pharmacology*; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000196:embryology / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D005576:Colforsin; D006165:Guanylyl Imidodiphosphate; D005934:Glucagon; D000262:Adenylyl Cyclases; D007545:Isoproterenol; D013755:Tetradecanoylphorbol Acetate