INSULIN-LIKE GROWTH-FACTOR-I (IGF-I) DELAYS THE ONSET OF DIABETES IN NONOBESE DIABETIC (NOD) MICE

It has been shown that prophylactic exogenous insulin treatment preven ts the development of insulin-dependent diabetes mellitus (IDDM) in an imal models and humans. In this study, we examined whether the develop ment of diabetes and insulitis in female non-obese diabetic (NOD) mice could be affected by prophylactic administration of insulin-like grow th factor I (IGF-I), which shares structural homology with insulin and has insulin-like metabolic effects. Two experiments which differed in duration and dosage of IGF-I treatment were carried out. In the first experiment, animals were treated from 4 to 9 weeks of age with IGF-I (17.9 nmol/day at 4-5 weeks of age and 35.9 nmol/day at 6-9 weeks of a ge) and observed up to 34 weeks of age. In the second experiment, the animals were treated from 4 to 34 weeks of age with IGF-I (1.79 nmol/d ay at 4-5 weeks of age, 3.59 nmol/day at 6-9 weeks of age, and 5.38 nm ol/day at 10-34 weeks of age). The former treatment could significantl y delay the onset of diabetes (P < 0.05) and decrease the insulitis sc ore at 10 weeks of age (P < 0.01). On the other hand, the latter treat ment did not affect the incidence of diabetes, the age at onset or the insulitis score. Our results suggest that the IGF-I treatment at the early age may provide protection against autoimmune beta-cell destruct ion in NOD mice.