DEVELOPMENTAL DIFFERENCES IN THE IGF-I SYSTEM RESPONSE TO SEVERE AND CHRONIC CALORIE MALNUTRITION

Recent studies in children suggest that there are age-related differen ces in the insulin-like growth factor I (IGF-I) response to malnutriti on. To extend this observation, immature 4-wk-old male rats were faste d for 3 days, fed ad libitum (control), or fed 60 or 40% of control ca lories (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 sta ble despite reduced insulin levels, whereas IGF-I increased 2.2-fold i n the younger controls. With the 40% diet, younger and older rats chan ged body weight +1 and -1 g body wt/day, respectively (P < 0.0001). Th e restricted younger animals reduced serum IGF-I, IGF binding protein- 3, acid-labile subunit, and growth hormone binding protein levels sign ificantly more than the restricted older animals. Fasting decreased mo st of these parameters by 40%, serum insulin by similar to 80%, and bo dy weight by 9%, regardless of age. We conclude that the suppression o f the IGF-I system in response to chronic undernutrition, but not acut e fasting, is greater in maturing than young adult rats.