The ability of the kidney to maintain constancy of glomerular filtration rate (GFR) over a wide range of renal perfusion pressures is termed autoregulation. Defective autoregulation of GFR has been demonstrated in patients with diabetic and non-diabetic nephropathy and in streptozotocin diabetic rats during hyperglycaemia. Information on the potential impact of acute changes in glycaemic control on autoregulation of GFR in diabetic patients is lacking. Therefore the aim of our study was to evaluate the effect of acute lowering of blood pressure (BP) on GFR during normoglycaemia and hyperglycaemia. We investigated 14 (12m/2f) normoalbuminuric patients with non-insulin dependent diabetes (NIDDM). The patients were examined in random order on two separate days with blood glucose (BG)<10 mmol/L or with BG>15 mmol/L. GFR (single shot [51Cr] EDTA plasma clearance technique) was measured twice each day; first without clonidine (baseline) followed by intravenous injection of clonidine 100-150 microg. We measured BG (One Touch 2), and BP (Takeda TM2420) several times during each GFR measurement. Clonidine reduced mean arterial blood pressure with 20 (1.4) vs. 16 (1.2) mmHg (mean (SE)) with BG<10mmol/L and with BG>15 mmol/L, respectively (p=0.053). GFR diminished in average from 92 (3.1) to 86 (3.7) ml/min/1.73m2 with BG<10 mmol/L (p<0.05), and from 102 (4.1) to 98 (4.2) ml/min/1.73 m2 with BG> 15 mmol/L, NS. Mean difference between changes in GFR (95% confidence interval) between the examination with BG<10 mmol/L and with BG>15 mmol/L were 2.3 (-1.3 to 5.9) ml/min/1.73 m2 (NS). The mean BG during normoglycaemia was 6.9 (0.3) vs.16.9 (0.4) during hyperglycaemia.
Conclusion: Our study suggests that acute changes in glycaemic control have no detectable effect on autoregulation of GFR in NIDDM patients. Hyperglycaemia enhances GFR.