Influence of sex, age and adrenergic pathways on the growth hormone response to GHRP-6.
OBJECTIVE
His-dTrp-Ala-Trp-dPhe-Lys-NH2 (GHRP-6) is a synthetic compound that releases GH in a dose-related and specific manner in several species including man. To further characterize the effects of GHRP-6 on GH secretion in normal human subjects, we assessed plasma GH levels following GHRP-6 administration in normal male adult subjects, normal female adult subjects at different stages of their menstrual cycle and in normal prepubertal male and female children. We also studied the influence of adrenergic pathways on GHRP-6 induced GH secretion in normal adult male subjects.


METHODS
In a group of eight volunteers the following tests were carried out: GHRP-6 alone (1 microgram/kg i.v. at 0 minutes); propranolol (40 mg p.o. at -30 minutes) plus GHRP-6; and prazosin (3 mg p.o. at -120 minutes) plus GHRP-6. Another group of eight volunteers were studied with GHRP-6 as above; clonidine alone (300 mg p.o. at -60 minutes); and clonidine plus GHRP-6. A group of nine women were studied with 1 microgram/kg i.v. of GHRP-6 at 0 minutes, at different stages of their menstrual cycle. Finally, 12 children were studied with GHRP-6 using the same dose and methods as above.


METHODS
Twenty-five normal adult subjects (16 male and nine female) and 12 normal prepubertal children (six male and six female) wer studied after giving informed consent.


METHODS
Plasma GH levels were measured by radioimmunoassay.


RESULTS
No differences in GH responses to GHRP-6 were found between children and normal adult male or female subjects at different stages of their menstrual cycle. Administration of propranolol and clonidine did not modify the GH responses to GHRP-6 in male adults. In contrast, prazosin administration induced an increase in plasma GH levels that was statistically different from that of GHRP-6 alone (. < 0.05 between area under curve).


CONCLUSIONS
GHRP-6 exerts a potent stimulatory effect on GH secretion in adults and children. Its effects, at least at the dose studied, are independent of sex and age. Noradrenergic pathways through alpha 2 adrenergic receptors are unlikely to influence this response.
Peñalva
A
A
Department of Medicine, Faculty of Medicine, University of Santiago de Compostela, Spain.
Pombo
M
M
Carballo
A
A
Barreiro
J
J
Casanueva
F F
FF
Dieguez
C
C
D000328:Adult; D000367:Age Factors; D002648:Child; D003000:Clonidine / Q000494:pharmacology; D004347:Drug Interactions; D005260:Female; D013006:Growth Hormone / Q000097:blood / Q000187:drug effects*; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology*; D006728:Hormones / Q000494:pharmacology; D006801:Humans; D008297:Male; D008597:Menstrual Cycle / Q000097:blood; D009842:Oligopeptides / Q000494:pharmacology*; D011224:Prazosin / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D012737:Sex Factors
D006728:Hormones; D009842:Oligopeptides; C041048:growth hormone releasing hexapeptide; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D011433:Propranolol; D003000:Clonidine; D011224:Prazosin