Decreased distal acidification in acute hypercapnia in the dog

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Abstract
The effect of acute hypercapnia on distal nephron H+ secretion (DNH+S) in vivo by means of the urine-blood PCO2 [partial pressure of CO2] difference (U-B PCO2) in alkaline urine. Bicarbonaturia was induced by either a sodium bicarbonate infusion or L-lysine administration. The U-B PCO2, as a function of the urinary HCO3 concentration, was significantly lower during acute respiratory acidosis; this effect was not dependent on changes in glomerular filtration rate and/or fractional excretion of Na, K and Cl. Infusion of the Na salts of sulfate, a nonreabsorbable anion, did not correct the diminished U-B PCO2. Amiloride caused the U-B PCO2 to fall in normocapnic dogs but not in hypercapnic dogs. When hypercapnia was superimposed in dogs with extracellular fluid volume contraction, there were no changes in the U-B PCO2. Apparently, acute hypercapnia in the intact dog decreases DNH+S and is compatible with an effect of hypercapnia on the voltage-dependent component of urine acidification. The mechanism appears to be direct rather than secondary to factors that influence the rate of Na delivery to the distal nephron.