Structural requirements for the activation of rat anterior pituitary adenylate cyclase by growth hormone-releasing factor (GRF): discovery of (N-Ac-Tyr1, D-Arg2)-GRF(1-29)-NH2 as a GRF antagonist on membranes.
The efficacy and potency of 14 GH-releasing factor (GRF) analogs, substituted in position 1 to 7, on adenylate cyclase activation in crude homogenates from rat anterior pituitary were related to those of human pancreatic GRF(1-29)-amide and vasoactive intestinal peptide. Among several D-amino acid substitutions, that in position 2 was the only one to yield a super-agonist [with a Kact (concentration required for half-maximal adenylate cyclase activation) 2 times lower than that of GRF(1-29)-NH2]. By contrast, D-isomer substitution in position 1 and 3 was without effect and D-isomer substitution in position 4, 6, or 7 decreased the affinity of the analog. The N-acetylated analog of GRF was as potent and active as the parent peptide, and the identity of the amino acid in position 2 of (N-Ac-Tyr1)-GRF(1-29)-NH2 proved to be determining for enzyme activation, with D-Phe2 and D-Trp2 derivatives acting as partial agonists and the (N-Ac-Tyr1,D-Arg2) analog being an efficient competitive antagonist of GRF(1-29)-NH2. With use of this antagonist, it was possible to demonstrate that GRF and vasoactive intestinal peptide receptors represent distinct entities in the rat anterior pituitary.
D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D013007:Growth Hormone-Releasing Hormone / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D008297:Male; D010446:Peptide Fragments / Q000494:pharmacology; D010903:Pituitary Gland, Anterior / Q000502:physiology*; D051381:Rats; D011956:Receptors, Cell Surface / Q000187:drug effects*; D018013:Receptors, Neuropeptide; D018017:Receptors, Pituitary Hormone-Regulating Hormone; D018005:Receptors, Vasoactive Intestinal Peptide; D013329:Structure-Activity Relationship; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
D010446:Peptide Fragments; D011956:Receptors, Cell Surface; D018013:Receptors, Neuropeptide; D018017:Receptors, Pituitary Hormone-Regulating Hormone; D018005:Receptors, Vasoactive Intestinal Peptide; C039542:somatocrinin receptor; D014660:Vasoactive Intestinal Peptide; D013007:Growth Hormone-Releasing Hormone; D000262:Adenylyl Cyclases