1. Effective renal plasma flow, glomerular filtration rate and cardiac output were measured in osmotically loaded dogs before and during comparable acute respiratory and metabolic acidosis.

2. Urine output increased in control dogs and in animals with metabolic acidosis, but declined with respiratory acidosis. Effective renal plasma flow and glomerular filtration rate declined with respiratory and metabolic acidosis.

3. When respiratory acidosis was buffered with sodium bicarbonate, urine volume increased and glomerular filtration rate and effective renal plasma flow were unchanged; with trihydroxymethylaminomethane, urine volume increased but glomerular filtration rate and effective renal plasma flow fell.

4. When metabolic acidosis was buffered with sodium bicarbonate, urine volume increased; with trihydroxymethylaminomethane, urine volume increased but glomerular filtration rate fell. Cardiac output declined only during metabolic acidosis, both buffered and unbuffered.

5. These studies demonstrate that, even with osmotic loading: (1) respiratory acidosis causes a decrease in glomerular filtration rate, effective renal plasma flow and urine volume; (2) metabolic acidosis depresses glomerular filtration rate and effective renal plasma flow but does not change urine volume even though cardiac output falls; (3) sodium bicarbonate is more effective than trihydroxymethylaminomethane in preserving renal function during respiratory and metabolic acidosis.

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