Short-term suppression of elevated growth hormone concentrations following insulin-like growth factor 1 administration in young adults with type 1 diabetes does not alter glomerular filtration or albumin excretion rates

Objective: Young adults with type 1 diabetes mellitus (T1DM) have increased glomerular filtration rate (GFR), which may mediate progressive renal disease and microalbuminuria. This may be secondary to low concentrations of insulin-like growth factor (IGF)-I and GH hypersecretion. We tested the hypothesis that restoration of circulating IGF-I concentrations in young adults with T1DM might suppress GH secretion, GFR and urinary albumin excretion. Design: In a randomized double blind crossover study six young adults with T1DM (three men, 19-24 years) received 7 days treatment with rhIGF-I/insulin-like growth factor binding protein (IGFBP)-3 complex (SomatoKine®) 0·4 mg/kg/day and placebo. Subjects underwent overnight insulin infusion for euglycaemia, followed by determination of GFR and albumin excretion rate. Results: Following IGF-I/IGFBP-3 complex, overnight insulin requirements (0·15 vs placebo 0·21 mU/kg/min, P < 0·04), plasma insulin (77 vs placebo 152 pmol/l, P < 0·01) and mean overnight GH (2·6 vs placebo 4·8 mU/l, P < 0·04) fell. IGF-I (492 vs placebo 218 ng/ml, P < 0·01) and IGFBP-3 (4·5 vs placebo 3·9 μg/ml, P < 0·05) increased. GFR did not change (145·5 (23·9) ml/min/1·73 m² post-IGF-I/IGFBP-3 complex vs 152·2 (19·8) post placebo). Albumin excretion rate did not change 9·5 (5·5-16·6)mg/24 h pre- vs 11·5 (9·9-20·2) post-IGF-I/IGFBP-3 complex and 10·7 (8·1-21·2) pre- vs 11·5 (8·7-29·9) post placebo. Plasma creatinine levels were lower following IGF-I/IGFBP-3 complex (mean ± SD, 56·2 ± 16·8 μmol/l) vs placebo (61·5, 45·0, P < 0·02). Conclusions: Seven days treatment with IGF-I/IGFBP-3 complex enhanced overnight insulin sensitivity and reduced GH levels, but there was no effect on glomerular hyperfiltration or albumin excretion rates.