IGF-I does not affect the net increase in GH release in response to arginine.
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.
Nass
Ralf
R
Division of Endocrinology and Metabolism, Department of Medicine, University of Virginia, Charlottesville, Virginia 22908, USA.
Pezzoli
Suzan S
SS
Chapman
Ian M
IM
Patrie
James
J
Hintz
Raymond L
RL
Hartman
Mark L
ML
Thorner
Michael O
MO
D000328:Adult; D001120:Arginine / Q000008:administration & dosage*; D001786:Blood Glucose; D005215:Fasting / Q000502:physiology; D005260:Female; D005947:Glucose / Q000008:administration & dosage; D019382:Human Growth Hormone / Q000097:blood* / Q000378:metabolism*; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000008:administration & dosage* / Q000009:adverse effects; D008297:Male
D001786:Blood Glucose; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I; D001120:Arginine; D005947:Glucose