Effect of High Hydrostatic Pressure on Smooth Muscle Part Ⅰ. On the longitudinal muscle of frog intestine

When high hydrostatic pressure (50 to 500 kg/㎠) was applied to isolated longitudinal muscle strip (10 to 15 mm long, 2 to 3 mm wide) of frog intestine hanging in Ringer's solution, following changes of its length and rhythmical movement were observed. 1) Under high hydrostatic pressure up to 100 kg/㎠ the rhythmical movement of the strip is accelerated in frequency and tonus effectively, depending on neurogenic nature, and at 300 to 500 kg/㎠ it weakens or disappears. 2) When the pressure of about 300 to 500 kg/㎠ is applied to the muscle strip, it lengthens quickly at first and then conversely shortens gradually after a certain limit of extension, and again the strip contracts rapidly but temporarily and then relaxes slowly. 3) These lengthening and subsequent shortening of the strip under high hydrostatic pressure of 300-500 kg/㎠ seem to to of myogenic nature and not of neurogenic nature