The kidney responds to respiratory acidosis by altering the fractional clearance of chloride as against sodium in pregnant ewes

Abstract

Using Stewart’s physiochemical acid-base theory, we hypothesized that the kidney will balance the net excretion of chloride as against sodium in response to acute respiratory acidosis. The experiment was performed in pregnant ewes on days 118 and 125 of gestation. Ewes were placed in carts where the head resides within a sealed plexiglass chamber. Inspired CO2 concentration was manipulated for 1 hour to produce acute respiratory acidosis. When the arterial partial pressure of carbon dioxide (PaCO2) and pH changed from 32 ± 1 mm Hg and 7.52 ± 0.02 at the 0th hour to 74 ± 2 mm Hg and 7.22 ± 0.02 respectively at the 1st hour, the renal fractional clearance of chloride with respect to sodium increased significantly by 71 ± 28%. The clearance returned to baseline at 2nd hour when PaCO2 and pH were 37 ± 0.6 mm Hg and 7.49 ± 0.01 respectively. Thus, we conclude that the renal response to respiratory acidosis is to increase the strong ion difference by differential reabsorption of sodium and chloride. Since sodium reabsorption is strongly related to renal regulation of extracellular fluid volume, net chloride excretion relative to sodium is the primary mechanism for renal regulation of acid-base balance. Supported by NIAAA 10940 (T.A.C.) and the Pediatric Initiatives.