Endocrinology, Vol 134, 562-567, Copyright © 1994 by Endocrine Society

ARTICLES

Role of growth hormone (GH)-releasing hormone and somatostatin in the mediation of clonidine-induced GH release in sheep

E Magnan, M Cataldi, V Guillaume, L Mazzocchi, A Dutour, H Razafindraibe, N Sauze, M Renard and C Oliver
Laboratoire de Neuroendocrinologie Experimentale, INSERM U-297, Institut Federatif Jean Roche, Faculte de Medecine Nord, Marseille, France.

GH secretion is stimulated by the administration of an alpha 2- adrenergic agonist, clonidine, in several species, including man. This action is probably mediated at the level of the hypothalamus, where the drug may act through inhibition of somatostatin (SRIH) and/or stimulation of GH-releasing hormone (GHRH) release. We have investigated the mode and site of action of clonidine in sheep, because it is possible to collect hypophysial portal blood for the simultaneous determination of GHRH and SRIH in this species under conscious unstressed conditions. Clonidine injection (0.3 mg, iv) resulted in a significant, immediate, and short-lasting (30-min) increase in peripheral GH (14.4 +/- 3.1 vs. 4.8 +/- 1.1 ng/ml; P < 0.01) and portal GHRH (2.7 +/- 0.5 vs. 1.0 +/- 0.2 pg/min; P < 0.01) levels. No change in SRIH secretion was recorded during the same period. Next, we tested the effect of clonidine in sheep actively immunized against GHRH or SRIH. The alpha 2-adrenergic agonist did not affect GH secretion in the anti-GHRH group, whereas immunization against SRIH did not modify the GH response. Finally, we observed that clonidine did not influence GH release from cultured ovine pituitary cells. These data suggest that clonidine acts centrally to stimulate hypophysial GH secretion in the sheep and that this effect is mediated through changes in GHRH, but not SRIH, release into hypophysial portal blood.

This article has been cited by other articles:

				A. O. L. Wong, M. C. Y. Chuk, H. C. Chan, and E. K. Y. Lee Mechanisms for gonadotropin-releasing hormone potentiation of growth hormone rebound following norepinephrine inhibition in goldfish pituitary cells Am J Physiol Endocrinol Metab, January 1, 2007; 292(1): E203 - E214. [Abstract] [Full Text] [PDF]

				C Viguie, Y Chilliard, V Gayrard, N Picard-Hagen, P Monget, A Dutour, and P-L Toutain Alterations of somatotropic function in prion disease in sheep J. Endocrinol., November 1, 2004; 183(2): 427 - 435. [Abstract] [Full Text] [PDF]

				H. E. Pruett, D. L. Thompson Jr., J. A. Cartmill, C. C. Williams, and L. R. Gentry Thyrotropin releasing hormone interactions with growth hormone secretion in horses J Anim Sci, September 1, 2003; 81(9): 2343 - 2351. [Abstract] [Full Text] [PDF]

				J. E. Drisko, T. D. Faidley, D. Zhang, T. J. McDonald, S. Nicolich, D. F. Hora, P. Cunningham, C. Li, E. Rickes, L. McNamara, et al. Administration of a Nonpeptidyl Growth Hormone Secretagogue, L-163,255, Changes Somatostatin Pattern, But Has No Effect on Patterns of Growth Hormone-Releasing Factor in the Hypophyseal-Portal Circulation of the Conscious Pig Experimental Biology and Medicine, October 2, 1999; 222(1): 70 - 77. [Abstract] [Full Text]

				M. Russell-Aulet, C. A. Jaffe, R. DeMott-Friberg, and A. L. Barkan In Vivo Semiquantification of Hypothalamic Growth Hormone-Releasing Hormone (GHRH) Output in Humans: Evidence for Relative GHRH Deficiency in Aging J. Clin. Endocrinol. Metab., October 1, 1999; 84(10): 3490 - 3497. [Abstract] [Full Text] [PDF]

				C. A. Jaffe, B. W. Huffman, and R. Demott-Friberg Insulin hypoglycemia and growth hormone secretion in sheep: a paradox revisited Am J Physiol Endocrinol Metab, August 1, 1999; 277(2): E253 - E258. [Abstract] [Full Text] [PDF]

				A. Giustina and J. D. Veldhuis Pathophysiology of the Neuroregulation of Growth Hormone Secretion in Experimental Animals and the Human Endocr. Rev., December 1, 1998; 19(6): 717 - 797. [Abstract] [Full Text]