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

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 horm one (0.1, 0.2, 0.4 U kg(-1) body weight(-1)) in six patients with normal GF R under a euglycaemic clamp. We also examined a 24-h profile of plasma grow th hormone and IGF-1 during usual insulin therapy in two other groups each with seven patients with a lower (from 93 to 114 mi min(-1) (1.73 m(2))(-1) ) and higher (from 121 to 146 mi min(-1) (1.73 m(2))(-1)) GFR. Results. Plasma growth hormone concentrations peaked 2 h after its injectio n and plasma concentrations of IGF-1 peaked about 24 h after the growth hor mone injection. There was a significant increase in GFR and RPF 24 h after the highest dose of the growth hormone injection (corresponding to the high est IGF-1 concentration), from baseline values of 115 +/- 24 and 536 +/- 14 1 mi min(-1) (1.73 m(2))(-1) to 160 +/- 33 and 657 +/- 137 mi min(-1) (1.73 m(2))(-1), respectively (p < 0.01 for GFR and p < 0.05 for RPF). No differ ences were observed in the 24-h profile of growth hormone and IGF-1 plasma concentrations between the two groups; growth hormone and IGF-1 concentrati ons 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 h ormone-induced IGF-1 concentrations are required to modify renal haemodynam ics in Type I diabetic patients and suggest that, under the "physiological" conditions of diabetes, IGF-1 has no role as a mediator of glomerular hype rfiltration.