Physiological effects of portal ligation on the longitudinal and circular muscles of the dog portal tree.

We studied physiological effects of portal vein ligation on the longitudinal and circular muscles of the dog portal tree. Portal venous blood pressure after portal ligation was higher in dogs that died than in those that survived. The portal veins isolated from dogs that died after portal ligation exhibited both lower rate of onset and decreased intensity of spontaneous activity, compared with those from dogs that survived. Responsiveness of longitudinal muscles of each of the four portal segments to noradrenaline, acetylcholine, histamine and KCl was markedly reduced in dogs that died, compared with those that survived, although the responsiveness of circular muscle was nearly equal in both groups of dogs. The longitudinal muscle of the truncal portal vein from dogs that died responded less strongly to electrical transmural stimulation than that from surviving dogs. The nonadrenergic, noncholinergic response was almost abolished in dogs that died rapidly. The degree of spontaneous activity or responsiveness to various stimulations in smooth muscles of the portal tree is considered to reflect muscular development. The degree of development of the longitudinal muscle of the portal tree may determine the survival of dogs after portal ligation.