Carbonic anhydrase, MG 2+-HCO 3−-ATPase and MG 2+-NA +-K +-ATPase in rat intestinal mucosa: Effects of adrenalectomy and aldosterone administration

Abstract

The possible role of cytosol enzymes in rat intestinal mucosa (carbonic anhydrase. mitochondrial Mg 2+-HCO 3 −-ATPase and microsomal Mg 2+-Na +-K +-ATPase) as mediators of the action of aldosterone has been examined. The small intestinal tract was cut into seven segments from the duodenum to the distal end of the ileum. Each segment was 12–13 cm in length. The large intestine (colon and rectum) was combined and used as a single sample. Carbonic anhydrase and Mg 2+-HCO 3 −-ATPase activity was observed to be highest in the first segment of the small intestinal mucosa and gradually decreased in consecutive sections. Mg 2+-Na +-K +-ATPase activity was higher in the first three segments. Five days after adrenalectomy the activities of all three enzymes in the upper small and large intestine had significantly decreased. The administration of aldosterone (10–40 μg/kg; 4 h after ip injection) increased carbonic anhydrase activity in the upper small and large intestine as well as Mg 2+-HCO 3 −-ATPase activity in the upper small intestine. No significant elevation of Mg 2+-Na +-K +-ATPase activity was observed in any segment. The elevation of carbonic anhydrase and Mg 2+-HCO 3 −-ATPase activities by aldosterone was inhibited by pretreatment with cycloheximide. These results suggest that increases in the activity of both enzymes induced by aldosterone may be the result of enzyme synthesis which serves to regulate membrane transport of ions in the upper small intestine.