AJP - Endocrinology and Metabolism, Vol 241, Issue 3 196-E199, Copyright © 1981 by American Physiological Society
Regulation by catecholamines of spontaneous growth hormone secretion in the baboon
J. K. Stewart, D. J. Koerker, C. J. Goodner, C. C. Gale, M. F. Minton and R. A. Steiner
To gain an increased understanding of the role of central neurotransmitters
in the regulation of spontaneous growth hormone (GH) secretion in the
primate, we investigated the effects of peripheral intravenous infusion of
the alpha-adrenergic receptor-blocking agent, phentolamine (5.0-mg bolus
and 1.5 mg . kg-1 . 12 h-1), and the tyrosine hydroxylase inhibitor,
alpha-methyl-p-tyrosine (MPT, 300 mg . kg-1 . 24 h-1), on the pattern of GH
secretion in five adolescent male baboons. Serum GH concentrations were
measured in blood samples taken at 20-min intervals over 12 h (0530-1730)
after an overnight fast. In nontreatment control studies, GH secretion
exhibited a predictable rhythmic oscillation with a mean period of 5.7 +/-
0.4 (SE) h. Phentolamine significantly decreased the 12-h mean and
integrated GH concentrations compared to control values, but the small
peaks of GH, which could be distinguished from base-line concentrations in
three of the animals, occurred at the same time as during control studies.
Whereas alpha-methyl-p-tyrosine slightly reduced serum levels of GH, it
significantly increased the GH pulse frequency in the baboons. A two- to
fourfold increase in serum prolactin levels occurred in all animals treated
with MPT. These findings suggest that alpha-adrenergic pathways play a
stimulatory role in maintaining spontaneous daytime GH secretion in the
baboon and that one or more catecholamines are involved in the generation
of rhythmic GH release.
