Faculty Bibliography

Chronic parenteral mineralocorticoid and glucocorticoid treatment increases colonic sodium and water absorption and mucosal Na-K-ATPase activity. Cycloheximide, a protein synthesis inhibitor, was utilized to compare the mechanisms of action of these corticosteroids. Rats were injected with 50 or 100 micrograms/100 g body wet cycloheximide every 12 h, 0.5 or 3 mg/100 g deoxycorticosterone (DOCA) daily, or 3 mg/100 g methylprednisolone (MP) daily, singly or in combination for 2 days. In water absorption, transmural potential difference, and the specific activity of Na-K-ATPase were measured. Cycloheximide alone did not alter colonic water, sodium, or chloride absorption or Na-K-ATPase activity but did increase transmural potential difference. DOCA-induced increases in colonic absorption and Na-K-ATPase were completely prevented by cycloheximide. Cycloheximide completely prevented the increase in Na-K-ATPase in MP-treated rats but only partially reduced the MP-induced increase in sodium and water absorption. These results suggest that this enzyme is not the primary site of glucocorticoid action. It remains to be determined whether an increase in Na-K-ATPase activity is a necessary part of the maximal colonic response to chronic glucocorticoid treatment

The effects of acute respiratory alkalosis and acidosis on intestinal electrolyte transport were studied in adult Sprague-Dawley rats. During in situ intestinal perfusion, anesthetized animals were ventilated with 0, 3, or 8% CO2, creating states of alkalosis (pH 7.64 +/- 0.01), normocapnia (pH 7.45 +/- 0.01), or acidosis (pH 7.26 +/- 0.01), respectively. The plasma bicarbonate concentration decreased 2.0 mM during alkalosis and increased 2.1 mM during acidosis. The jejunum did not respond to the acid-base disturbances. In both the ileum and colon, alkalosis decreased the net absorption of water (-16%), sodium (-23%), and chloride (-42%) and the net secretion of bicarbonate (-33%), whereas acidosis had the opposite effect, i.e., the net absorption of water (41%), sodium (39%), and chloride (32%) increased as did net bicarbonate secretion (33%) (ileal values given). Changes in sodium chloride movement could be correlated with changes in systemic pH and CO2 tension (PCO2), and bicarbonate secretion paralleled changes in the plasma bicarbonate concentration. The acid-base disorders had no effect on ileal and colonic net potassium secretion and transmural potential difference. These studies suggest that systemic pH and/or PCO2 regulate sodium chloride absorption, and the plasma bicarbonate concentration regulates bicarbonate secretion