scholarly journals Age and Secretagogue Type Jointly Determine Dynamic Growth Hormone Responses to Exogenous Insulin-Like Growth Factor-Negative Feedback in Healthy Men

2004 ◽  
Vol 89 (11) ◽  
pp. 5542-5548 ◽  
Author(s):  
Johannes D. Veldhuis ◽  
Judith Y. Weltman ◽  
Arthur L. Weltman ◽  
Ali Iranmanesh ◽  
Eugenio E. Muller ◽  
...  
Keyword(s):  
Growth Hormone ◽  
Growth Factor ◽  
Negative Feedback ◽  
Insulin Like Growth Factor ◽  
Exogenous Insulin ◽  
Healthy Men ◽  
Hormone Responses ◽  
Dynamic Growth

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

2002 ◽  
Vol 283 (4) ◽  
pp. E702-E710 ◽  
Author(s):  
Ralf Nass ◽  
Suzan S. Pezzoli ◽  
Ian M. Chapman ◽  
James Patrie ◽  
Raymond L. Hintz ◽  
...  
Keyword(s):  
Growth Hormone ◽  
Young Adults ◽  
Growth Factor ◽  
Negative Feedback ◽  
Random Order ◽  
Feedback Effect ◽  
Insulin Like Growth Factor ◽  
Gh Secretion ◽  
Factor I ◽  
Igf I

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 μg · kg−1 · h−1recombinant 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.

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