Differential tissue regulation of insulin-like growth factor binding proteins in experimental diabetes mellitus in the rat.

The expression and regulation of IGF-I is tissue-specific in diabetes mellitus in the rat. These studies were designed to examine if similar tissue specificity exists for IGF-BPs in the diabetic milieu. Diabetes mellitus was induced by a single i.p. injection of STZ (100 mg/kg body weight). Rats were treated with either vehicle--insulin, vanadate, or phlorizin for 7-14 days. Tissues were analyzed for IGF-BPs by ligand blotting and by affinity cross-linking and immunoprecipitation. In liver tissue from nondiabetic control rats, multiple forms of IGF-BPs were noted, ranging from 48,000 to 25,000 M(r). In diabetic rat liver tissue, the 25,000-M(r) form was unchanged, whereas the higher M(r) forms (48,000-42,000 M(r)) were decreased, and the 30,000-M(r) form was increased. Insulin therapy of diabetic rats decreased all forms to below control levels. In the kidney tissue of control rats, faint IGF-BP bands were seen at 30,000 and 25,000 M(r). In diabetic rat kidney tissue, the 30,000-M(r) form again was increased (as in liver) and restored to control levels with insulin therapy. In contrast, only a 30,000-M(r) band was seen in control pituitary tissue, which was slightly increased in the diabetic rats and also was decreased below control levels by insulin. In hypothalamus and cerebral cortex tissue, bands at 30,000 and 25,000 M(r) were noted, and neither was altered by diabetes or insulin treatment. Treatment of diabetic rats with vanadate and phlorizin resulted in comparable blood glucose levels, which were only slightly higher than those achieved with insulin therapy.(ABSTRACT TRUNCATED AT 250 WORDS)