title: Lymphocyte adenylate cyclase and human aging.
abstract: Adenylate cyclase activity was determined by enzymatic conversion of [32P]ATP to [32P]cAMP using peripheral lymphocytes freshly isolated from human subjects. The lymphocyte enzyme was stimulated by the potent beta-adrenergic catecholamine agonist isoproterenol and by the nonhydrolyzable GTP-analog Gpp[NH]p. The two activators had a synergistic effect, and agonist-dependent enzyme activity followed simple Michaelis-Menten kinetics with respect to isoproterenol in the presence but not in the absence of Gpp[NH]p. Cyclic AMP production by intact lymphocytes, determined by protein binding assay, also followed simple Michaelis-Menten kinetics with respect to isoproterenol. Kact of isoproterenol was the same in intact cells and the broken cell assay in the presence of Gpp[NH]p, suggesting the indispensable role the GTP-binding coupling factors play in the intact lymphocyte. In 31 human subjects between the age of 21 and 103, adenylate cyclase activity in the presence of isoproterenol, Gpp[NH]p, or isoproterenol in the presence of Gpp[NH]p decreased with the increasing age of the subject. The sensitivity of the enzyme to stimulation by isoproterenol, defined as the Kact and determined in the presence of Gpp[NH]p, was the same in lymphocytes from young (less than 45 years) or elderly (greater than 75 years) subjects. These results suggest a deficiency in the lymphocyte adenylate cyclase system distal to the beta-adrenergic catecholamine receptor could account for deterioration of cAMP-mediated components of the immune response which occur with age.
mesh_terms: D000262:Adenylyl Cyclases / Q000097:blood*; D000328:Adult; D000368:Aged; D000375:Aging; D000242:Cyclic AMP / Q000097:blood; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005260:Female; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D008214:Lymphocytes / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D008875:Middle Aged
chemical_list: D006165:Guanylyl Imidodiphosphate; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D007545:Isoproterenol