Lactate and pyruvate metabolism in isolated renal tubules of normal dogs

Abstract

The kinetics of lactate and pyruvate (1 and 5 mM in each case) metabolism was studied in isolated dog renal tubules. Utilization of these two substrates and the production of glucose, pyruvate, or lactate, and alanine were determined. The rates of lactate and pyruvate utilization and of glucose production were constant during 60 min of incubation. Glucose production from pyruvate was less than that from lactate. Addition of albumin to the incubation medium greatly inhibited lactate and pyruvate utilization at both substrate concentrations. It stimulated, however, glucose production from 1 mM, but not 5 mM, lactate or pyruvate. These effects were found to be due to the presence of fatty acids in the albumin solution used. In the absence of fatty acids, glucose production represented 35 to 40% of lactate uptake, but represented less than 20% of pyruvate uptake. Fatty acids markedly enhanced the percentage of transformation of lactate and pyruvate into glucose, and that of pyruvate into lactate. Alanine represented 20% or less of lactate and pyruvate uptake. These results suggest that fatty acids have a regulatory influence on lactate and pyruvate dog kidney metabolism.

The Rabbit Kidney Tubule Simultaneously Degrades and Synthesizes Glutamate

“…Both in the absence and the presence of acetate, the labelings of the C-1 (singlet) of glutamate and glutamine and of alanine were almost identical when [5-13 C]glutamate or [1,2-13 C]glutamate was the substrate. Tables V and VI also show that, with [5-13 C]glutamate and [1,2-13 C]glutamate as substrate, both in the absence and the presence of acetate, the labeling of the C-1 (singlet) of glutamate, glutamine, and alanine was virtually half that of the C-2 of glutamate, glutamine, and alanine when [3][4][5][6][7][8][9][10][11][12][13] C]glutamate was the substrate (see Table IV). …”

“…Metabolite Assays-Glucose, glycogen, lactate, pyruvate, glutamate, glutamine, alanine, aspartate, citrate, ␣-ketoglutarate, fumarate, malate, glycerol, and glycerol 3-phosphate were determined by usual enzymatic methods, and the dry weight of tubules added to the flasks was determined as described previously (11,13). 13 C NMR Techniques-These were recorded at 100.6 MHz on a Bruker AM-400 WB spectrometer using a 10-mm broadband probe thermostated at 8 Ϯ 0.5°C.…”

“…Since the C-2 and the C-3 of the oxaloacetate derived from the added [3-13 C]glutamate were converted at the same rates to the C-3 and C-2 (respectively) of the glutamate synthesized and therefore to the C-3 and C-2 of the glutamine derived from the latter glutamate, one may calculate that with glutamate as sole substrate, a mean value of 67 mol/g dry wt of glutamine arose directly from the added [3-13 C]glutamate, whereas 10.8 mol/g dry wt of [3-13 C]glutamine derived from synthesized [3][4][5][6][7][8][9][10][11][12][13] C]glutamate (see Table IV); in the presence of [3-13 C]glutamate plus acetate, the corresponding values are 34.6 and 11.3 mol/g dry wt, respectively. The latter values obtained for estimating the direct accumulation of glutamine from added [3-13 C]glutamate in the absence and the presence of acetate are in relatively good agreement with those obtained by measuring the accumulation of [5-13 C]glutamine from [5-13 C]glutamate (Table V) as well as by measuring the multiplets (spin-spin 13 C coupling of C-1 and C-2) resulting from the synthesis of [1,2-13 C]glutamine from [1,2-…”

“…When [3][4][5][6][7][8][9][10][11][12][13] C]glutamate was the substrate in the absence and the presence of acetate, the labeling (in mol/g dry wt) of the different carbons of glucose (␣ ϩ ␤ anomers) was as follows: C-1, 2.2 Ϯ 0.5 and 3.4 Ϯ 0.2; C-6, 1.8 Ϯ 0.5 and 2.6 Ϯ 0.1; C-2, 1.7 Ϯ 0.6 and 2.6 Ϯ 0.4; C-5, 2.5 Ϯ 0.9 and 4.5 Ϯ 0.2, respectively; the C-3 and C-4 were not enriched. When [5-13 C]-and [1,2-13 C]glutamate were the substrates, the C-3 and C-4 of glucose were enriched only in the presence of acetate; the values were 2.0 Ϯ 0.4 and 1.1 Ϯ 0.1 for the C-3, respectively; the corresponding values for the C-4 were 2.4 Ϯ 0.5 and 1.7 Ϯ 0.2, respectively.…”

“…Kidney cortex tubules were prepared by collagenase treatment of renal cortex slices as described by Baverel et al (11). Incubations other than those involving radioactive substrates were performed for 30 or 60 min at 37°C in a shaking water bath, in 25-ml stoppered Erlenmeyer flasks in an atmosphere of O 2 /CO 2 (19/1).…”