IGF-I does not affect the net increase in GH release in response to arginine

• Published in: American journal of physiology: endocrinology and metabolism Vol. 283; no. 4; p. E702
• Main Authors: Nass, Ralf, Pezzoli, Suzan S, Chapman, Ian M, Patrie, James, Hintz, Raymond L, Hartman, Mark L, Thorner, Michael O
• Format: Journal Article
• Language: English
• Published: United States 01-10-2002
• Subjects: Adult; Arginine - administration & dosage; Blood Glucose; Fasting - physiology; Female; Glucose - administration & dosage; Human Growth Hormone - blood; Human Growth Hormone - secretion; Humans; Insulin-Like Growth Factor I - administration & dosage; Insulin-Like Growth Factor I - adverse effects; Male
• ISSN: 0193-1849
• DOI: 10.1152/ajpendo.00075.2002

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.