Metabolic control of renal vascular resistance and glomerulotubular balance

Renal vascular resistance (RVR) and glomerulotubular balance were examined in isolated rat kidneys perfused at 100 mm Hg with 10 mM lactate (L) or 10 mM pyruvate (P) or 5 mM glucose (G) either alone or with a mixture of 20 amino acids (13.5 mM, AA); albumin oncotic pressure 24 +/- 1 mm Hg. RVR was L greater than P greater than G = AA. Vasodilation by G and AA was additive. Proximal tubular sodium-cotransport was evaluated from fractional reabsorption (FR) of phosphate (Pi), G, and L. FR Pi was 91% in AA, 86% in P, 72% in L, and 67% in G. Combining AA or P with L or G increased FR Pi to 89 to 90%. FRs of G and L by G and L perfused kidneys were 83 and 78%, respectively, and were increased to 97 to 99% by combining G or L with AA or P. P and AA also increased FR sodium and FR water when combined with L or G or when combined with each other. GFR correlated positively with FR sodium and FR water. AA combined synergistically with L to increase gluconeogenesis. These results indicate that, compared with pyruvate or AA, neither glucose nor lactate alone is a good energy source for proximal tubular reabsorption, that synergistic interactions between AA or pyruvate and lactate or glucose augment GFR by increasing proximal tubular reabsorption, and that the vasodilating effects of glucose and AA are not related directly to their effects on GFR.