In the first human study of renal autoregulation Parving et al.  studied Type 1 diabetic patients with and without diabetic nephropathy. They found no significant change in GFR during acute lowering of BP with clonidine in patients without clinical signs of microangiopathy. The patients had mean blood glucose less than 13 mmol/l during the investigation . In the first study of Type 2 diabetic patients with and without diabetic nephropathy  no significant change in GFR during acute lowering of BP in normoalbuminuric Type 2 diabetic patients was revealed. Mean blood glucose was less than 10 mmol/l during this investigation. The above-mentioned studies were not designed to evaluate the potential effect of acute changes in blood glucose on autoregulation of GFR. In a randomised crossover study of GFR autoregulation, in normoalbuminuric type 2 diabetic patients during blood glucose < 10 mmol/l ("normoglycaemia") and during acute blood glucose > 15 mmol/l (hyperglycaemia) . Acute reduction in systemic BP induced a mean (SE) reduction in GFR from 92 (3.1) to 86 (3.7) ml/min/1.73 m2 during "normoglycaemia" (p<0.05), whereas the reduction in GFR during hyperglycaemia was from 102 (4.1) to 98 (4.2) ml/min/1.73 m2, NS). Mean difference between the mean reductions in GFR during the two examinations was 2.3 (95% CI, -1.3 to 5.9) ml/min/1.73 m2, NS. The significant reduction in GFR during "normoglycaemia" might be explained by a more profound reduction in MABP compared to the examination during hyperglycaemia. However, it is possible that hyperglycaemia enhances renal autoregulation (shift the autoregulation range to the left (fig 1.)) as described by Mauer et al. .
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