rhIGF-I Administration Reduces Insulin Requirements, Decreases Growth Hormone Secretion, and Improves the Lipid Profile in Adults With IDDM

IDDM is associated with elevated circulating levels of growth hormone (GH) and reduced insulin-like growth factor I (IGF-I). GH antagonizes the action of insulin-increasing insulin requirements in IDDM. The effects of subcutaneously administered rhIGF-I on glycemie control, insulin requirements, and GH secretion were studied in eight adults with IDDM. Patients received either placebo or rhIGF-I (50 pg/kg b.i.d.) for 19 days in a randomized, double-blind, parallel-design, placebo-controlled trial. Overnight GH, plasma glucose, free insulin, IGF-I, fructosamine, and lipid profiles were assessed during this period. rhIGF-I therapy increased IGF-I concentration from 117.1 ± 14.2 (mean ± SE) ng/ml (baseline) to 310.5 ± 40.6 and 257.1 ± 41.2 ng/ml on day 5 (P < 0.01 vs. baseline) and day 20 (P < 0.01 vs. baseline), respectively. After 19 days of rhIGF-I treatment, fructosamine concentrations were unchanged compared with baseline (439 ± 32 vs. 429 ± 35 μmol/l, day –1 vs. day 20, respectively), yet insulin requirements were decreased by ∼45% (0.67 ± 0.08 vs. 0.36 ± 0.07 U · kg⁻¹ · day⁻¹, day –1 vs. day 19, respectively, P < 0.005). After 4 days of rhIGF-I therapy, there was a decrease in free insulin levels (8.38 ± 1.47 vs. 4.98 ± 0.84 mU/l, P < 0.05), mean overnight GH concentration (12.6 ± 3.3 vs. 3.8 ± 2.1 mU/l, P = 0.05), and total cholesterol and triglycerides (4.68 ± 0.31 vs. 4.25 ± 0.35 mmol/l, P < 0.05, 1.27 ± 0.19 vs. 0.95 ± 0.21 mmol/l, P < 0.001, respectively). There was no change in any variable in the placebo-treated patients. This study demonstrates that subcutaneous administration of rhIGF-I decreases insulin requirements and improves the plasma lipid profile while maintaining glycemie control in adults with IDDM. The excess nocturnal release of GH, characteristic of IDDM, is also decreased by rhIGF-I therapy. Exogenous rhIGF-I therapy may have a role in the treatment of adults with IDDM, particularly in the setting of abnormal lipids and a high insulin requirement.