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Type: Journal article
Title: IGF-I does not affect the net increase in GH release in response to arginine
Author: Nass, R.
Pezzoli, S.
Chapman, I.
Patrie, J.
Hintz, R.
Hartman, M.
Thorner, M.
Citation: American Journal of Physiology: Endocrinology and Metabolism, 2002; 283(4):E702-E710
Publisher: Amer Physiological Soc
Issue Date: 2002
ISSN: 0193-1849
Statement of
Ralf Nass, Suzan S. Pezzoli, Ian M. Chapman, James Patrie, Raymond L. Hintz, Mark L. Hartman, and Michael O. Thorner
Abstract: Arginine stimulates growth hormone (GH) secretion, possibly by inhibiting hypothalamic somatostatin (SS) release. Insulin-like growth factor I (IGF-I) inhibits GH secretion via effects at the pituitary and/or hypothalamus. We hypothesized that if the dominant action of IGF-I is to suppress GH release at the level of the pituitary, then the arginine-induced net increase in GH concentration would be unaffected by an IGF-I infusion. Eight healthy young adults (3 women, 5 men) were studied on day 2 of a 47-h fast for 12 h (35th-47th h) on four occasions. Saline (Sal) or 10 microg. kg(-1). h(-1) recombinant human IGF-I was infused intravenously for 5 h from 37 to 42 h of the 47-h fast. Arginine (Arg) (30 g iv) or Sal was infused over 30 min during the IGF-I or Sal infusion from 40 to 40.5 h of the fast. Subjects received the following combinations of treatments in random order: 1) Sal + Sal; 2) Sal + Arg; 3) IGF-I + Sal; 4) IGF-I + Arg. Peak GH concentration on the IGF-I + Arg day was ~45% of that on the Sal + Arg day. The effect of arginine on net GH release was calculated as [(Sal + Arg) - (Sal + Sal)] - [(IGF-I + Arg) - (IGF-I + Sal)]. There was no significant effect of IGF-I on net arginine-induced GH release over control conditions. These findings suggest that the negative feedback effect of IGF-I on GH secretion is primarily mediated at the pituitary level and/or at the hypothalamus through a mechanism different from the stimulatory effect of arginine.
Keywords: growth hormone
insulin-like growth factor I
Description: © 2002 American Physiological Society
DOI: 10.1152/ajpendo.00075.2002
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