Renal regulation of bicarbonate loads during hypothermia

¹ Department of Physiology, Albany Medical College, Albany, New York

The ability of the hypothermic kidney to handle massive exogenous bicarbonate loads was studied in five dogs given 2.6% NaHCO₃ plus 0.75% creatinine and 0.1% PAH intravenously at the rate of 4.0 ml/min. The renal hemodynamic pattern was typical of hypothermia with decreasing GFR, RPF, and blood pressure and increasing renal resistance. Urine pH rose to 7.95 while arterial pH, corrected to body temperature, reached a maximum of 7.56 and then slowly declined to 7.51 at 27 C. In spite of the fall in GFR, the urine flow, under the influence of the hyperosmotic load, increased progressively throughout the exposure. Although the bicarbonate load presented to the tubules remained near control levels throughout most of the exposure, the absolute reabsorption of bicarbonate fell from a normothermia value of 1.5 mEq/min to 0.9 mEq/min at 27 C. In terms of mEq of bicarbonate reabsorbed/100 ml of glomerular filtrate, bicarbonate reabsorption increased from 2.1 mEq/min at 38 C to 2.7 mEq/min at 27 C. On the basis of the progressive increase in the clearance ratio for bicarbonate, from a normothermia value of .15 to .34 at 27 C, it is concluded that a depressing effect of cold on the tubular transport of bicarbonate had occurred.

Note:
With the Technical Assistance of R. H. Lubinski and I. M. Mielens