Role of insulin-like growth factor (IGF)-1 in the modulation of renal haemodynamics in Type I diabetic patients

Abstract

Aims/hypothesis. We investigated in normotensive Type I (insulin- dependent) diabetic patients with normoalbuminuria the role of growth hormone-induced IGF-1 in the modulation of renal haemodynamics. Methods. We measured glomerular filtration (GFR) and renal plasma flow (RPF) at baseline and at 24 h after injection of different doses of growth hormone (0.1, 0.2, 0.4 U · kg-1 · body weight-1) in six patients with normal GFR under a euglycaemic clamp. We also examined a 24-h profile of plasma growth hormone and IGF-1 during usual insulin therapy in two other groups each with seven patients with a lower (from 93 to 114 ml · min-1 · (1.73 m2)-1) and higher (from 121 to 146 ml · min-1 · (1.73 m2)-1) GFR. Results. Plasma growth hormone concentrations peaked 2 h after its injection and plasma concentrations of IGF-1 peaked about 24 h after the growth hormone injection. There was a significant increase in GFR and RPF 24 h after the highest dose of the growth hormone injection (corresponding to the highest IGF-1 concentration), from baseline values, of 115 ± 24 and 536 ± 141 ml · min-1 · (1.73 m2)-1 to 160 ± 33 and 657 ± 137 ml · min-1 · (1.73 m2)-1 respectively (p < 0.01 for GFR and p < 0.05 for RPF). No differences were observed in the 24-h profile of growth hormone and IGF-1 plasma concentrations between the two groups; growth hormone and IGF-1 concentrations were lower than those obtained after the injection of 0.4 U. kg-1 · body weight-1 of growth hormone. Conclusion/interpretation. These results show that pharmacological growth hormone-induced IGF-1 concentrations are required to modify renal haemodynamics in Type I diabetic patients and suggest that, under the 'physiological' conditions of diabetes, IGF-1 has no role as a mediator of glomerular hyperfiltration.