title: Beta-adrenergic receptors, glucagon receptors, and their relationship to adenylate cyclase in rat liver during aging.
abstract: The beta-adrenergic and glucagon receptor-binding capacities in rat livers from 6-27 months of age were measured to investigate the mechanism of a previously observed rise in beta-adrenergic stimulated adenylate cyclase with increasing age. There was no concomitant increase in glucagon-stimulated adenylate cyclase. In the present study neither glucagon-binding capacity nor glucagon-stimulated adenylate cyclase changed with age. In contrast, the beta-adrenergic receptor capacity, measured in the same membranes by [125I]iodopindolol binding, increased nearly 3-fold from 6.6 +/- 0.6 fmol/mg at 6 months to 19.1 +/- 3.3 fmol/mg at 18-19 months. The increase was directly proportional to the maximum isoproterenol-stimulated adenylate cyclase activity in livers of rats up to 19 months of age. By 24-27 months the binding capacity had increased to 24.9 +/- 3.3 fmol/mg, but there was no further increase in adenylate cyclase activity. Thus, there appeared to be a beta-receptor-adenylate cyclase uncoupling in livers from the senescent animals (25-27 months). The defect could not be demonstrated by studies examining isoproterenol competition of [125I]iodopindolol from agonist-induced high affinity sites on the membranes, a procedure that examines receptor-Ns protein coupling. Activation of adenylate cyclase by the nonhormonal stimulators F- and forskolin did not change with age, indicating that the catalytic unit was not a limiting factor. Since the relationship between the glucagon receptor and adenylate cyclase also remained unaltered, the uncoupling apparently lies in an alteration of the interaction between the beta-adrenergic receptor and the guanine nucleotide-sensitive Ns protein.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D000375:Aging / Q000378:metabolism*; D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005934:Glucagon / Q000378:metabolism; D006150:Guanine Nucleotides / Q000494:pharmacology; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D008099:Liver / Q000378:metabolism*; D008297:Male; D010869:Pindolol / Q000031:analogs & derivatives / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D011964:Receptors, Gastrointestinal Hormone / Q000378:metabolism*; D018027:Receptors, Glucagon; D012969:Sodium Fluoride / Q000494:pharmacology
chemical_list: D006150:Guanine Nucleotides; D011943:Receptors, Adrenergic, beta; D011964:Receptors, Gastrointestinal Hormone; D018027:Receptors, Glucagon; D005576:Colforsin; D006165:Guanylyl Imidodiphosphate; C029247:3-iodopindolol; D012969:Sodium Fluoride; D005934:Glucagon; D010869:Pindolol; D000262:Adenylyl Cyclases; D007545:Isoproterenol