AJP - Endocrinology and Metabolism, Vol 270, Issue 4 E646-E653, Copyright © 1996 by American Physiological Society

ARTICLES

Developmental differences in the IGF-I system response to severe and chronic calorie malnutrition

M. H. Oster, N. Levin, P. J. Fielder, I. C. Robinson, R. C. Baxter and M. J. Cronin
Endocrine Research, Department of Genentech, South San Francisco, California 94080, USA. oster@gene.com

Recent studies in children suggest that there are age-related differences in the insulin-like growth factor I (IGF-I) response to malnutrition. To extend this observation, immature 4-wk-old male rats were fasted for 3 days, fed ad libitum (control), or fed 60 or 40% of control calories (restricted) and compared with 8-wk-old young adults. Over the 3-wk study period, serum total IGF-I levels of the older rats were stable despite reduced insulin levels, whereas IGF-I increased 2.2-fold in the younger controls. With the 40% diet, younger and older rats changed body weight +1 and -1 body wt/day, respectively (P < 0.0001). The restricted younger animals reduced serum IGF-I IGF binding protein-3, acid-labile subunit, and growth hormone binding protein levels significantly more than the restricted older animals. Fasting decreased most of these parameters by 40%, serum insulin by approximately 80%, and body weight by 9%, regardless of age. We conclude that the suppression of the IGF-I system in response to chronic undernutrition, but not acute fasting, is greater in maturing than young adult rats.

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