Insulin in the regulation of insulin-like growth factor binding protein-3 in healthy men and patients with Type 1 diabetes mellitus

Insulin-like growth factor binding protein-3 carries most of the circulatin g IGFs, While insulin regulates serum IGFBP-1 concentration, the effect of insulin on IGFBP-3 concentration is not known. We examined the IGFBP-3 resp onse to hyperinsulinemia in healthy subjects and diabetic patients. Serum I GFBP-3 and IGF-I concentrations were measured during a 4-hour euglycemic hy perinsulinemia (1.5 mU/kg/min) in 17 healthy men (age 26+/-1 yr, BMI 23.5+/ -0.6 kg/m(2)) and in 20 men with type 1 diabetes mellitus (T1DM) (age 29+/- 2 yr, BMI 22.7+/-0.4 kg/m(2), duration 14+/-2 yr, HbA(1c) 7.9+/-0.3%). Fast ing serum IGFBP-3 concentrations were similar in the healthy (4172+/-232 mu g/l) and diabetic subjects (3925+/-271 mu g/l), and inversely related with age in both groups. Fasting serum IGFBP-3 concentration correlated positiv ely with insulin in both groups and with GH in the diabetic patients. Insul in infusion resulted in a 9.7% reduction of IGFBP-3 in healthy subjects (p< 0.05), and a 4.2% decline in the diabetic patients (p=0.05), GH concentrati ons did not change significantly, In regression analysis in healthy men, ag e alone accounted for 33% (p=0.01) and insulin level alone for 32% (p=0.01) of the variation in the fasting IGFBP-3 concentration, Together they expla ined 49% of the variation in IGFBP-3 (p<0.01). In the diabetic group, age a lone explained 43% (p=0.001) and GH alone 22% (p<0.05) of the variation in IGFBP-3 concentration, Fasting serum IGF-I levels were similar in the healt hy (23.1-1.6 mnol/l) and diabetic subjects (25.0+/-1.8 nmol/l) and remained unaffected by the insulin infusion. In conclusion: 1) Fasting IGFBP-3 and IGF-I concentrations are similar in healthy and well controlled T1DM men an d decrease by age in both groups, 2) Acute hyperinsulinemia decreases serum IGFBP-3, but not IGF-I concentrations. This reduction is not associated wi th changes in serum GH levels. Diab. Nutr. Metab. 11:273-278, 1998. (C) 199 8, Editrice Kurtis.