Effect of acute metabolic alkalosis and acidosis on intestinal electrolyte transport in vivo

Abstract

The effects of acute metabolic alkalosis and acidosis on intestinal electrolyte transport were studied in adult Sprague-Dawley rats. Animals were made alkalotic or acidotic by gavage feeding of 1 M solutions of NaCl (pH = 7.42), NaHCO3 (pH = 7.52), NH4Cl (pH = 7.18) or 0.75 M (NH4)2SO4 (pH = 7.21). After 1-3 h, animals were anesthetized and prepared for in vivo perfusion of the jejunum, ileum and colon. The jejunum exhibited increased net K absorption in alkalosis and decreased K absorption in acidosis. In the ileum, net Na absorption and K secretion were decreased and bicarbonate secretion was increased in alkalosis and opposite effects were observed in acidosis. The ileal lumen minus blood gradient for PCO2 [partial pressure of CO2] (an index of H+ secretion) was greater in acidotic than in alkalotic animals.The levels of ileal Na, bicarbonate and K transport and the PCO2 gradient correlated well with the plasma pH and bicarbonate concentration in individual animals. In the colon, net bicarbonate secretion and Cl- absorption increased and K secretion decreased in alkalosis and opposite effects were observed in acidosis. The colonic lumen minus blood PCO2 gradient was not affected by acid-base balance. Colonic bicarbonate transport correlated with the plasma Cl- concentration and with the plasma pH. The acid-base disorders had no effect on transmural potential difference. Acute metabolic alkalosis and acidosis probably alter Na and H+ transport in the ileum and Cl- and bicarbonate transport in the colon.