Effect of bradykinin on transepithelial transfer of sodium and water in vitro

Mucosal sodium and water transfer were measured in everted sacs of rat jejunum. 2. Bradykinin (7.86 X 10(-12)M), when present in both mucosal and serosal solutions, produced a biphasic effect on mucosal sodium and water transfer. When basal transfer was low a stimulation was observed whereas an inhibition of transfer was observed when basal transfer was high. Bradykinin at concentrations of 7-86 X 10(-11) and 7-86 X 10(-13) M produced qualitatively similar effects. 3. Inhibition of transfer was observed whether bradykinin was present in the mucosal, serosal or both solutions. Stimulation of transfer was observed only when bradykinin was present in the serosal solution. 4. Theophylline (1 mM), alone inhibited water transfer at high and intermediate levels of basal transfer, and significantly potentiated the inhibitory effect of bradykinin (7-86 X 10(-12)M) on water transfer at intermediate levels of control transfer. 5. Cyclic AMP (1 mM) inhibited water transfer when basal transfer was high. Dibutyryl cyclic AMP (1 mM) inhibited water transfer at all levels of basal transfer. Dibutyryl cyclic AMP (1 mM) and bradykinin (7-86 X 10(-12)M) together produced a significantly greater inhibition of water transfer than either agent alone, at intermediate basal transfer. 6. It was observed that the action of bradykinin upon sodium and water transfer consists of two different and opposing effects. It is possible that the inhibitory effect of bradykinin upon water transfer is related to increased cyclic AMP activity.