title: Decreased stimulation of adenylate cyclase by growth hormone-releasing factor in the anterior pituitary of old rats.
abstract: Adenylate cyclase activity was studied in anterior pituitary homogenates from young adult (6 months) and old (20 and 24 months) male rats. Basal, NaF-, GTP-, 5'-guanylimidodiphosphate (Gpp(NH)p)- and forskolin-stimulated activities were similar in the three groups, implying that the stimulatory guanyl nucleotide regulatory binding site (NS) and the catalytical unit were unaffected by aging. Vasoactive intestinal peptide (VIP)-stimulated adenylate cyclase activity was also identical in the three groups. The efficacy (i.e., the maximum effect) of growth hormone-releasing factor [GRF(1-29)-NH2] on adenylate activity was reduced by 45-49% in old and senescent rats with no change in peptide potency (i.e., the concentration required for half-maximal enzyme stimulation). These results suggest that aging induced a selective loss of functional GRF receptors but influenced neither the coupling between receptors, NS and the catalytic unit nor the efficacy of the catalytic unit per se.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D000375:Aging / Q000378:metabolism*; D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology*; D006160:Guanosine Triphosphate / Q000494:pharmacology; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D008297:Male; D010903:Pituitary Gland, Anterior / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains; D012969:Sodium Fluoride / Q000494:pharmacology; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
chemical_list: D005576:Colforsin; D006165:Guanylyl Imidodiphosphate; D014660:Vasoactive Intestinal Peptide; D006160:Guanosine Triphosphate; D012969:Sodium Fluoride; D013007:Growth Hormone-Releasing Hormone; D000262:Adenylyl Cyclases