Control of renal hemodynamics in hyperglycemia: possible role of tubuloglomerular feedback.

The purpose of this study was to test the hypothesis that hyperglycemia, comparable with that found in uncontrolled diabetes mellitus, increases renal blood flow (RBF) and glomerular filtration rate (GFR) through a tubuloglomerular feedback (TGF) mechanism. We infused glucose intrarenally (0.1-0.3 g/min) into anesthetized dogs with normal kidneys (NK), with nonfiltering kidneys (NFK) in which changes in TGF were blocked, and with normal kidneys in which renal perfusion pressure (RAP) was lowered to the limits of renal autoregulation (LPK). Calculated intrarenal plasma glucose levels rose to 250-400 mg/dl. In NK (n = 6) RBF and GFR increased by 18 +/- 3 and 19 +/- 5%, respectively, and renal vascular resistance fell by 17 +/- 2% after 90 min. The renal hemodynamic responses to glucose were abolished in NFK (n = 8); RBF averaged 96 +/- 4% of control after 60 min of hyperglycemia. RBF and GFR did not change during hyperglycemia in LPK (n = 5), averaging 96 +/- 1 and 100 +/- 8% of control, respectively, after 60 min. Autoregulation of RBF and GFR during reductions in RAP was impaired during hyperglycemia in NK; RBF and GFR were effectively autoregulated between RAP of 126 and 70-85 mmHg during the control period, whereas during glucose infusion RBF and GFR fell by 31 +/- 9 and 47 +/- 10%, respectively, when RAP was reduced in steps to 70 mmHg. These data suggest that hyperglycemia impairs renal autoregulation and may increase renal blood flow and GFR through a tubuloglomerular feedback mechanism.