Dynamic stiffness of the isolated guinea-pig gall-bladder during contraction induced by cholecystokinin

The visco-elastic properties of the isolated guinea-pig gall-bladder were investigated by the dynamic method. The sinusoidal volume changes (up to 0.2 ml) and the resulting sinusoidal pressure changes were displayed on the cathode ray oscilloscope, the volume being on abscissa and the pressure on ordinate. The frequencies of the sinusoidal change in volume were 0.17-0.5 Hz which were 10 times higher than those in Schoetz et al.'s work (Am. J. Physiol. 241: G376-G381, 1981). The dynamic pressure-volume relation of the resting gall-bladder was nearly linear, but showed the elliptical hysteresis loop during CCK- or ACh-induced contractions. If frequencies of the sinusoidal change in volume were increased to 1.7-3.3 Hz, the hysteresis loop for either relaxing or contracting gall-bladder became narrow and guiter-shaped. The dynamic stiffness, the slope of the hysteresis loop or the ratio of the maximum of pressure change to the maximum of volume change, increased in linear proportion to intraluminal pressure rise during contraction. The data could be analysed on the assumption that the visco-elastic property of the gall-bladder was explained by two Voigt models placed in series. The one indicated the property of the smooth muscle tissue, and it had low elastance at the resting state, or middle-grade elastance together with high viscous resistance at the contraction state. Another one had high elastance and low viscous resistance, and it was characterized by collagen fibers involved within the organ.