[Behavior of the renal functional reserve in type I diabetic patients: effect of ACE-inhibition]

Abstract

Renal functional reserve capacity was evaluated in 19 normotensive type I diabetics without microalbuminuria. All patients had normal basal renal function as assessed by 24-hour creatinine clearances higher than 120 ml/min. PAH, inulin, and creatinine clearances were carried out every hour before, during, and after infusion of an amino acid (AA) solution. The same experiment was repeated after ACE inhibition with captopril (25 mg). Two groups of patients were found: Group A (responders) showed a significant rise in GFR after AA infusion (inulin clearances from 117 +/- 8 to 138 +/- 10 ml/min) (p less than 0.05), whereas in Group B (non-responders) no significant change in GFR was observed. Groups were comparable in age, duration of diabetes, metabolic control, and mean arterial blood pressure. Group B, however, had a significantly higher basal inulin clearance (167 +/- 17 ml/min) than Group A (117 +/- 8 ml/min). In Group A ACE inhibition completely blocked the AA-induced rise in GFR, while basal GFR in Group B was significantly reduced (167 +/- 17 to 148 +/- 8 ml/min) after captopril administration. In both groups renal plasma flow was enhanced by ACE inhibition. A rise in glucagon was observed in all patients during AA infusion. It is concluded that type I diabetics with normal basal renal function already have reduced (Group A) renal functional reserve capacity, which is completely abolished (Group B) when concomitant hyperfiltration occurs. ACE inhibition reduces hyperfiltration and is capable of blocking the AA-induced rise in GFR in these patients.