“…The hepatic portal vein of some mammals (mouse, rat, guinea pig, rabbit, and cat) is known to show rhythmical spontaneous contractions with a frequency of 3-30 per min, as well as a propagation of the contractile wave toward the liver (Attardi, 1955a,b;Booz, 1959;Funaki and Bohr, 1964;Holman et al, 1968;Johansson and Ljung, 1967a,b;Mislin, 1963Mislin, , 1969. Histological studies of the vessel wall have revealed the occurrence therein of smooth muscle cells, leading to the general assumption that the latter are the only muscular element responsible for portal vein contraction (Hammersen and Jungst, 1968;Holman et al, 1968;Ts'ao et al, 1970;Schipp et al, 1971).…”