Renal concentrating operation in hypothermic dogs

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Abstract
The renal concentrating operation during hydropenia and during constant infusion of 2 m urea in isotonic saline was studied in 10 anesthetized dogs. PAH, exogenous creatinine and osmolal clearances were determined, as well as rates of Na and Cl excretion. Following two to four control periods body temperature was lowered to approximately 25°C by the use of an ice-water bath. The above measurements were then repeated during this steady state of hypothermia. PAH and creatinine clearances are reduced to approximately one-third of control values, while urine flow is not significantly changed. Thus, proportionately less filtered water is reabsorbed. Osmolal clearance is reduced, but this reduction is less than that of GFR so that a decrease in the tubular reabsorption of filtered osmotic particles occurs in hypothermia. This reduction in tubular reabsorption of solute is revealed further in a two to threefold increase in the percentage excretion of filtered NaCl and total osmotic substance. A greater decrease in the process which removes free water (TcHH2O) from the supposedly isotonic tubular fluid results in a reduction to one-third to one-fourth of the control values for TcHH2O. There would appear to be a dissociation of water and solute reabsorptions in hypothermia which indicates a decrease in the renal concentrating process.

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