Effects of portasystemic shunting on visceral and portal blood flow in the dog.

Late effects of portasystemic shunting on visceral and portal vein blood flows were evaluated in mongrel dogs with radioactive microspheres. Sham operation (n = 5) produced no significant long-term changes in visceral blood flow. In contrast, there was a significant increase in small bowel perfusion 3 wk after selective and nonselective portasystemic shunting: end-to-side (n = 7), side-to-side (n = 7), H-graft mesocaval (n = 5), and distal splenorenal (n = 11). Variable increases in pancreatic blood flow were noted in all shunt groups. Portal venous blood flow was significantly elevated in all dogs with total shunts and was substantially increased in animals with H-grafts. Compared with baseline levels, perfusion of organs left in continuity with the portal vein after splenorenal shunting was significantly increased. Blood flow from the small bowel was primarily responsible for the magnitude of the change in portal venous flow. The reduction in hepatic perfusion by portal venous blood appears to trigger these compensatory responses. A humoral mediator best explains the phenomena observed.