Hyperglycemia and angiotensin-mediated control of the renal circulation in healthy humans

Type 1 and type 2 diabetics have an enhanced renal vasodilator response to angiotensin-converting enzyme (ACE) inhibition despite suppressed plasma renin activity (PRA), indicating possible activation of the intrarenal renin angiotensin system. To investigate the role of hyperglycemia, we evaluated the renal hemodynamic response to ACE inhibition in 9 healthy subjects in high-salt balance after steady-state hyperglycemia (8.4+/-1 mmol/L) was achieved via intravenous glucose administration. Renal plasma flow (RPF) and glomerular filtration rate (GFR) responses to captopril and to angiotensin II (Ang II) were measured as paraminohippuric acid and inulin clearances. Hyperglycemia produced a significant increase in RPF of 117 mL.min(-1).1.73 m(-2) after 90 minutes but not GFR, Administration of captopril at a dose of 25 mg during glucose infusion led to an increase in RPF of 173+/-24 mL.min(-1).1.73 m(-2) (P<0.01) but did not significantly change RPF in the absence of hyperglycemia (7+/-21 mL.min(-1).1.73 m(-2)). Captopril did not alter GFR in the presence or absence of hyperglycemia. Ang II infusion during hyperglycemia decreased RPF by 45+/-16 mL.min(-1).1.73 m(-2), and this was significantly enhanced by captopril (-98+/-26 mL.min(-1).1.73 m(-2), P<0.05). In contrast, there was no enhancement of the vasoconstrictor response to Ang II in the absence of hyperglycemia. PRA did not change with hyperglycemia. Enhancement of renal vasodilation during hyperglycemia by captopril without alteration of PRA suggests activation of the intrarenal renin angiotensin system.