Inhibition of Renal Tubular Function by Cold

¹ From the Department of Biochemistry, Louisiana State University School of Medicine, New Orleans, Louisiana

In an attempt to inhibit the renal tubular production of NH₃ and CO₂, alligators were exposed for long periods of time to temperatures as low as 5°C. Cold increased the concentration of the urinary Na, Cl, Ca, Mg and glucose while it decreased the excretion of NH₃, CO₂ and phosphate. When the effect was maximal the composition of the urine closely resembled that of the plasma except for a decreased protein and somewhat elevated CO₂ content. The fact that the injection of Diamox into cold alligators was necessary to reduce the CO₂ to the plasma level would seem to indicate that carbonic anhydrase was not totally inhibited by cold. Although cold reduced the clearances of both thiosulfate and creatinine, their U/P ratios of about 6/1 were not affected by temperature changes. Since PO₄ is normally excreted by the tubules of the alligator, this ion was injected to test the effect of cold on tubular excretion. With the decrease in temperature the PO₄ U/P ratio fell from 30/1 to 5/1. It was concluded that cold almost eliminates renal tubular activity in the alligator. Several experiments were also performed on turtles with similar results.

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