CECUM OF GUINEA-PIG IS A RESERVOIR AND SIGMOID IS A HIGH-RESISTANCE CONDUIT

We compared the filling responses of the cecum and the sigmoid of the guinea pig using volumes up to 60 ml and 2.5 ml, respectively. In the isolated cecum, each l-cm increment of hydrostatic pressure above zero led to accommodation of 10 ml volume; in the sigmoid, the yield press ure (at which accommodation first occurred) was 6 cm H2O, and pressure increments up to 20 cm H2O produced volume increments of less than 0. 5 ml. Resting pressure at half-maximal filling was 5.0 +/- 0.7 cm H2O for the sigmoid and 1.7 +/- 0.6 cm H2O for the cecum. K+ depolarizatio n led to a significant upward shift in the pressure curves of both seg ments. Ca2+ withdrawal decreased sigmoid and cecal pressures at some v olumes. Distension of the cecum triggered intermittent contractions, w hich began with the shortening of the teniae and were associated with low-amplitude pressures and expulsion of a 5- to 10-ml volume. Distens ion of the sigmoid produced propagating contractions that were associa ted with high-amplitude pressures and lengthening; compartmentalizatio n in the sigmoid prevented efflux from it, and volume inflow was not a ffected by pressure waves. Our observations indicate that its large ca pacity and great distensibility make the cecum suitable for reservoir functions, whereas its narrowness and lack of distensibility make the sigmoid a high-resistance conduit.