Identification of a pituitary growth hormone-releasing peptide (GHRP) receptor subtype by photoaffinity labeling.
Hexarelin, an analogue of GHRP-6, in which D-Tryptophan has been replaced by its 2-methyl derivative, is known to release growth hormone (GH) in vivo and in vitro by direct action on receptors present in anterior pituitary cells. Measurement of second messengers (c-AMP, Ca++, IP3) upon somatotrophs stimulation, suggests the existence of more than one GHRP receptor subtype. In order to document such an hypothesis, we have used a new photoactivatable derivative of Hexarelin, Tyr-Bpa-Ala-Hexarelin. This derivative was shown to be fully active in the release of GH in vivo with neonate rats. Using this photoactivatable ligand, we have specifically labeled a protein with an apparent Mr of 57,000 in human, bovine and porcine anterior pituitary membranes. Hexarelin and the spiroindoline sulfonamide MK-0677 displaced the Mr-57,000 photolabeled band with an apparent ED50 of 6x10(-7) M and 2x10(-5) M respectively. Taking into account the high efficiency (>60%) of covalent incorporation of the Bpa residue, this photoactivatable Hexarelin derivative has allowed the identification of a pituitary GHRP receptor subtype, which is apparently distinct from the recently cloned GH secretagogue receptor.
Ong
H
H
Faculty of Pharmacy, University of Montréal, Canada.
McNicoll
N
N
Escher
E
E
Collu
R
R
Deghenghi
R
R
Locatelli
V
V
Ghigo
E
E
Muccioli
G
G
Boghen
M
M
Nilsson
M
M
D000818:Animals; D002417:Cattle; D006031:Glycosylation; D006801:Humans; D008970:Molecular Weight; D009842:Oligopeptides / Q000378:metabolism; D019920:Photoaffinity Labels; D051381:Rats; D018013:Receptors, Neuropeptide / Q000145:classification*; D018017:Receptors, Pituitary Hormone-Regulating Hormone / Q000145:classification*; D013552:Swine
D009842:Oligopeptides; D019920:Photoaffinity Labels; D018013:Receptors, Neuropeptide; D018017:Receptors, Pituitary Hormone-Regulating Hormone; C086184:hexarelin; C048250:somatotropin releasing hormone receptor