Ion transport by the pig colon: effects of time and anesthesia

A method for temporarily isolating a 50-cm loop of ascending spiral colon in the pig allowed a study of the effect of halothane anesthesia on colonic absorption without complications of acute surgical trauma, and provided a means to obtain timed samples of the colonic solution. Test solutions instilled into the loop consisted of a volatile fatty acid solution, similar in composition to normal colonic contents, and a Ringer solution. Ther was no apppreciable change in the rate of net solute absorption in conscious or anesthetized animals in repeated 1-hour determinations over a 6-hour period, provided the cardiovascular and arterial acid base variables remained stable. Net rates and direction of individually transported solutes and H20 were essentially unaffected by anesthesia during 2-hour experimental periods. However, net solute changes in this closed-loop system were not constant during individual absorption periods. These changes were due to a volume dependence on the rate of net absorption and a rapid dissipation of the driving forces initially present. Failure to recognize these time-dependent changes may leas to serious misinterpretations of the results.