Adaptive changes in renal acidification in response to chronic respiratory acidosis

To examine whether chronic respiratory acidosis results in adaptive changes in renal acidification, rats were housed for 3 days in an environmental chamber with an ambient CO2 content of 10% and their kidneys were perfused in vitro according to two protocols. To assess hydrogen ion secretory capacity of the distal nephron, perfusions were carried out with a low bicarbonate concentration, in the absence of ammoniagenic substrate, and with saturating quantities of the buffer creatinine. Under these conditions, the titration of creatinine at a pH less than 6.0 (TA pH 6.0) reflects the H+ secretory capacity of a discrete functional segment of the distal nephron. Kidneys from rats with chronic respiratory acidosis exhibited a significantly lower urine pH and higher rate of TA pH 6.0 than controls perfused in this fashion, indicative of an adaptive increase in the distal nephron capacity for proton transport. This adaptation was comparable with that reported previously for rats exposed to chronic metabolic acidosis. Furthermore, evidence of adaptation persisted in the presence of amiloride (10(-5) M), suggesting that it reflects, at least in part, a sodium-independent mechanism of proton transport. Hydrogen ion secretion by the proximal nephron was assessed by performing standard bicarbonate titration curves with kidneys from rats with chronic respiratory acidosis, chronic metabolic acidosis, and controls using a perfusate equilibrated with 95% O2/5% CO2.(ABSTRACT TRUNCATED AT 250 WORDS)