Ion transport by the pig colon: effects of theophylline and dietary sodium restriction.

The effect of theophylline on colonic electrolyte transport was examined in an isolated, static loop system of the pig colon. The presence of theophylline abolished the net absorption of Na and water and increased the net secretion of HCO3. The net absorption of C1 or acetate was unaffected. In pigs adapted to a saltfree diet, the net absorption of Na was increased twofold from that observed in pigs fed the normal diet; however, the basal rate of net HCO3 secretion was unchanged. In the presence of theophylline, the saltfree diet restored net Na absorption to control levels, whereas the theophylline-induced increase in the rate of net HCO3 secretion was sustained. Results suggest that the relative rates of net Na and HCO3 transport are partially controlled by independent systems and indicate that normal rates of net absorption can be restored in the presence of a parallel secretory process.