Abstract
Summary: In order to study the maturation of the glucose reabsorptive process by the fetal kidney, nine chronic fetal lamb Preparations (0.66-3.72 kg) were studied and values compared to data obtained from four nonpregnant ewes. Blood and urine control values showed there was a close relationship between fetal glomerular filtration rate (GFR mllmin) and fetal body weight (r = 0-78, P < 0.02). The fractional excretion of sodium, during control periods, varied from 3.86-14.76%, but no relation with fetal weight or fetal GFR ml/min was found. The mean value for blood glucose observed at threshold was higher in the fetus (200 ± 13.3 mg/100 ml) than in adult ewes (177 ± 2.8 mg/100 ml). Fetal glucose threshold was correlated to fetal body weight (r = 0.71, P < 0.05) and fetal GFR ml/min (r = 0.74, P < 0.025). The maximum amount of glucose reabsorbed expressed per unit of GFR (TmG/GFR) was reached only in One fetus and was 4.73. In all other fetuses, TmG was not reached since metabolic acidosis developed during the murse of glucose infusion. However, in those fetuses, the highest amount of glucose reabsorbed expressed per unit of GFR (TG/GFR), before glucose infusion was stopped, varied from 2.32 to 3.85 with a mean of 2.83 ± 0.26. In the adult ewes TmG/GFR varied from 1.94 to 2.47, and the mean value (2.21 ± 0.12) was significantly lower (P > 0.05) than the mean TmG/GFR and TG/GFR values found in fetuses. These data indicate that the plasma threshold values for glucose reabsorption by the fetal kidney increased with fetal GFR, suggesting that (here is a parallel development in fetal tubular and glomerular function. Moreover, the fact that fetal TmG/GFR and TG/GFR were higher than adult TmdGFR suggests that there is no functional correlate to the documented anatomic glomerular preponderance during fetal life.
Speculation: The higher capacity of the fetal renal tubule to reabsorb glucose may be explained both by a prolonged transit time of the glomerular fdtrate through the proximal tubule and an increase in proximal tubular volume. However, the capacity of the distal tubule to reabsorb glucose, the degree of permeability of the fetal renal tubule, and the importance of inner versus outer nephrons need to be evaluated in order to determine their effect on the renal capacity of the fetal kidney to reabsorb glucose.
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Robillard, J., Sessions, C., Kennedy, R. et al. Maturation of the Glucose Transport Process by the Fetal Kidney. Pediatr Res 12, 680–684 (1978). https://doi.org/10.1203/00006450-197805000-00013
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DOI: https://doi.org/10.1203/00006450-197805000-00013
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