This study examined urinary acidification shortly after recovery from chronic hypocapnia induced by hypoxemia. Distal acidification was evaluated by measuring the urinary P(CO2) and urine-blood P(CO2) difference (U-B P(CO2)) when blood P(CO2) had returned to normal. In posthypocapnic rats, maximal alkalinization of the urine by acute sodium bicarbonate loading failed to increase urine P(CO2) and U-B P(CO2) to the level of posthypoxemic control rats and normal control rats with comparable blood pH and urine bicarbonate concentration. To test the hypothesis that decreased distal hydrogen ion secretion in posthypocapnic rats resulted from intracellular alkalosis secondary to protracted hypocarbia, posthypocapnic rats were exposed to hypercapnia of brief duration (30 min) and prolonged duration (120 min) in an attempt to restore distal acidification to normal. In posthypocapnic rats, hypercapnia of brief duration was associated with a significant increase in urine P(CO2) and a fall in urine pH. Prolonged hypercapnia resulted in a marked increase in urine P(CO2) and a further fall in urine pH. At any urinary bicarbonate concentration, however, the urine P(CO2) and U-B P(CO2) posthypocapnic rats exposed to hypercapnia were still significantly lower than in normal control rats identically subjected to prolonged hypercapnia and with comparable blood P(CO2) and blood pH. Our findings indicate that distal acidification after abrupt recovery from chronic hypocapnia is decreased as if the kidneys were still under the influence of hypocapnia. These findings could not be ascribed to extracellular alkalemia but could be explained by postulating that decreased urinary acidification resulted from persistence of cell alkalinity secondary to the accumulation of non-CO2 buffers generated during protracted hypocarbia. Alternatively, factors other than cell pH could mediate the adaptive decrease in distal hydrogen ion secretion of posthypocapnic rats.
|Original language||English (US)|
|Journal||American Journal of Physiology - Renal Fluid and Electrolyte Physiology|
|State||Published - Jan 1 1983|
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