Renal effect of tris (hydroxymethyl)aminomethane during CO₂ load

¹ Department of Anesthesiology, College of Physicians and Surgeons, Columbia University, New York City

Renal studies were made on ten dogs treated with an infusion of tris(hydroxymethyl)aminomethane (THAM) during a CO₂ load induced by apneic oxygenation. There was a 5 fold increase in diuresis with no significant change in inulin clearance. The urine-plasma osmolal ratio approached unity and there was a rapid elimination of the infusate demonstrating that THAM acts largely as an osmotic diuretic. The clearance of THAM was similar to that of inulin until plasma levels exceeded 19 mEq/liter. At that time the amount of THAM eliminated exceeded the filtered load indicating tubular excretion. The percentage of the filtered load of K excreted increased from 24 to more than 100% and, in spite of a rising pCO₂, the tubular reabsorption of bicarbonate reached a plateau after 20 min indicating that when THAM penetrates into the tubular cell, it interferes with the (H⁺) – (Na⁺) exchange mechanism. After 1 hr 35% of the THAM given had been excreted and after 4 days up to 93% had been recovered in the urine. The amount of ionized THAM excreted approximated the cationic deficit within 10%. There was a significant net increase in H⁺ excretion which paralleled the elimination of ionized THAM (R.NH₃⁺).