Changes in an electroneutral transport process mediated by angiotensin II in the rat distal colon in vivo

The purpose of these experiments was to determine if angiotensin II mediates the stimulation of water transport in the rat distal colon via an electroneutral mechanism. Amphotericin B (36 micrograms/ml) added to the mucosal surface of the colon significantly increased potential difference (pd) and short circuit current (scc) and significantly decreased resistance. Replacement of the luminal contents of the colon with 150 mM choline chloride decreased pd and scc while resistance remained unchanged. Increased colon resistance occurred on cooling the animals. Thus both increased and decreased pd, scc, and resistance could be measured with the preparation used in this study. The distal colon in vivo is sensitive to angiotensin II since low infusions (7 pmol/kg . min) stimulate water transfer 180% above controls. Transmural pd, resistance, and scc were measured in the distal colon, while the response to the hormone was monitored by measurement of jejunal water transport in the same animals, Intravenous infusion of angiotensin II at a subpressor dose (7 pmol/kg . min) significantly stimulated jejunal water absorption in the absence of any change in transmural pd, resistance, or scc measured in the distal colon. However, infusion of a pressor dose of angiotensin II (700 pmol/kg . min) significantly inhibited jejunal water absorption but again did not alter the electrical properties of the distal colon. These data suggest that angiotensin II can stimulate and inhibit intestinal water transport via electroneutral mechanisms. Thus, the actions of this hormone contrast with that of aldosterone, which stimulates intestinal sodium and water transport by electrogenic mechanisms.