Glomerulotubular balance following saline loading in the developing canine kidney

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Abstract
Glomerulotubular relationships for glucose were studied in the developing kidney before and after saline loading in 13 anesthetized puppies that were 2–51 days of age and in one adult. When volume expansion, plasma glucose concentrations of more than 500 mg/dl, and changes in sodium excretion (FENa) were avoided, the ratio of maximal tubular reabsorption of glucose (TmGlc)/inulin clearance (CIn) was 3.37 +/- 0.28 (means +/- SD) in the puppies and did not change with age. Following intravenous saline loading (20 ml/kg), TmGlc and sodium reabsorption decreased, CIn decreased, and TmGlc/CIn decreased to 2.97 +/- 0.67. When a volume equivalent to the saline load had been excreted, TmGlc increased, CIn and FENa did not change, and TmGlc/CIn increased to 3.60 +/- 1.00. Splay in the glucose titration curve did not change with age, but the portion of the curve at saturation decreased with saline loading and returned to the control pattern as the saline load was excreted. It is concluded that glomerulotubular balance for glucose obtains from birth in the dog kidney, and that saline loading results in functional glomerulotubular imbalance with glomerular preponderance and alters the appearance of the glucose titration curve.