Effects of glucose and insulin on metabolism and function of perfused rat kidney

Abstract

Insulin increased fractional renal Na reabsorption (%.ovrhdot.TNa), but it was not established whether increases in renal glucose metabolism accompanied this action. Isolated rat kidneys were perfused for 75 min with a Krebs-Ringer-bicarbonate solution containing 6% substrate-free albumin (SFA) to which was added either nothing (NS), insulin, 26 mU[unit]/ml (NS + I), 10 mM glucose (G), or 10 mM glucose + 26 mU/ml insulin (G + I). Insulin increased the glucose decarboxylation rate (P = 0.002) from 0.23 .+-. 0.01 .mu.mol/min per g (G) to 0.32 .+-. 0.01 .mu.mol/min per g (G + I), but insulin had not effect on net lactate production rate (P > 0.6) or on net glucose utilization rate (P = 0.056). Compared to NS: NS + I had no effect on absolute Na reabsorption rate (.ovrhdot.TNa) or glomerular filtration rate (GFR); mean GFR increased from 519 .+-. 24 .mu.l/min per g (with NS) to 729 .+-. 20 .mu.l/min per g with G(P < 0.001); %.ovrhdot.TNa increased from 60.7 .+-. 1.5% with NS to 71.1 .+-. 1.1% with G(P < 0.001). Compared to G, in the presence of G + I: mean GFR was not increased (780 .+-. 23 .mu.l/min per g; P > 0.3) while %.ovrhdot.TNa was increased to 78.1 .+-. 1.3% (P < 0.001). The ratio of the .DELTA..ovrhdot.TNa/glucose oxidation rate due to the presence of G was 126 .+-. 10 .mu.eq/.mu.mol; the additional increments in .ovrhdot.TNa and glucose oxidation which occurred with G + I resulted in a similar ratio, 136 .+-. 8 .mu.eq/.mu.mol. The bulk of the increases in .ovrhdot.TNa due to the presence of G or of G + I could not be attributed to the co-transport of Na with glucose. The observations are consistent with the tight coupling of glucose oxidation to .ovrhdot.TNa.