Demonstration and characterization of the specific binding of growth hormone-releasing peptide to rat anterior pituitary and hypothalamic membranes.
Since the growth hormone-releasing peptide (GHRP), His-D-Trp-Ala-Trp-D-Phe-Lys-NH2, was found to specifically release growth hormone by a complementary but yet not clearly defined action on the pituitary as well as the hypothalamus, in vitro studies have been performed to demonstrate and characterized GHRP binding sites on peripheral membranes of both the rat anterior pituitary and hypothalamus. Optimum binding assay conditions were established using [125I]Tyr-Ala-GHRP as the radioligand. The membrane binding sites were specific, reversible, saturable and time, temperature, pH and concentration dependent. Computerized analyses of competition experiments suggested two classes of binding sites in both pituitary and hypothalamic membranes. The maximum specific binding was observed at pH 5.0 than the physiological pH in both tissues. Pretreatment of the membranes with trypsin prevented specific binding. The increase in Bmax was statistically significant and showed a 2.0- to 8.9-fold and 5.8- to 11.2-fold in pituitary and hypothalamus, respectively, whereas the affinity constants (Kds) were not significant. Of the synthetic and natural neuropeptides that influence the release of GH from somatotrophs, only (D-Lys3)GHRP, substance P antagonists and growth hormone-releasing factor analog were potent inhibitors of GHRP binding in both tissues.
Sethumadhavan
K
K
Department of Medicine, Tulane University Medical School, New Orleans, Louisiana 70112.
Veeraragavan
K
K
Bowers
C Y
CY
D000595:Amino Acid Sequence; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D013007:Growth Hormone-Releasing Hormone / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D007031:Hypothalamus / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D010903:Pituitary Gland, Anterior / Q000378:metabolism*; D018013:Receptors, Neuropeptide; D017981:Receptors, Neurotransmitter / Q000187:drug effects / Q000378:metabolism*; D018017:Receptors, Pituitary Hormone-Regulating Hormone; D013373:Substance P / Q000031:analogs & derivatives / Q000494:pharmacology; D013816:Thermodynamics
D018013:Receptors, Neuropeptide; D017981:Receptors, Neurotransmitter; D018017:Receptors, Pituitary Hormone-Regulating Hormone; D013373:Substance P; D013007:Growth Hormone-Releasing Hormone; C048250:somatotropin releasing hormone receptor