MUCOSAL DISTORTION BY COMPRESSION ELICITS POLARIZED REFLEXES AND ENHANCES RESPONSES OF THE CIRCULAR MUSCLE TO DISTENSION IN THE SMALL-INTESTINE

The possibility that distortion of the mucosa by compression might be a sufficient stimulus to evoke reflex responses in intestinal muscle, and that such reflexes might summate with distension-evoked (stretch) reflexes, was tested in isolated segments of guinea pig small intestine. Opened segments of intestine were pinned flat in an organ bath with, or without, distending balloons embedded in its base. Intracellular microelectrode recordings were taken from the circular muscle oral and anal to sites of application of sensory stimuli. Pressure against the mucosa, which distorts the villi without the wall being stretched, evoked polarized reflex responses in the circular muscle, consisting of excitatory junction potentials oral and inhibitory junction potentials anal to the stimulus. Distension stimuli applied by 6-mm diameter balloons that pushed against either the serosal or the mucosal surface also evoked excitatory junction potentials in the muscle oral to the stimulus and inhibitory junction potentials at anal sites. Response amplitudes were 20% greater when the distending balloon pushed against the mucosal surface. Responses to distension from the serosal side were 20% greater amplitude when combined with mucosal distortion by compression than without such compression. It is concluded that peristaltic movements that are commonly studied in the small intestine can be consequences of reflexes elicited at the same time from mucosal distortion receptors and from stretch receptors.