Portal venular constriction during anaphylactic shock in anesthetized rats.

Hepatic venoconstriction occurs in rat anaphylactic hypotension. However, the exact venoconstrictive site remains unknown, and we therefore attempted to determine its location by using hepatic venography and histology. Anaphylaxis was induced in anesthetized Sprague-Dawley rats by i.v. administration of ovalbumin antigen. Venography of the portal vein (n = 8) was obtained at baseline and maximal hepatic venoconstriction. We separately examined photomicrographs of the liver sections. Along with systemic hypotension, portal venous pressure increased to a peak of 28 ± 3 cm- H2O at 2 min after antigen injection. Post-antigen portal venography revealed that 40% of portal venuls (76 vessels/total 188 vessels) with diameters from 160 to 300 μm were not visualized, suggesting that stenosis or obliteration occurred distally. The corresponding upstream portal vessels exhibited markedly bulging. Stenosis was also observed in some portal branches with diameters from 180 to 420 μm (9%; 17 vessels/total 188 vessels). Light microscopically, most portal venules with an estimated baseline diameter less than 110 μm showed stenosis, but statistically significant stenosis was found in those with baseline diameters of 20-70 μm. In conclusion, anaphylactic hepatic venoconstriction occurs over a wide range of portal veins with diameters less than 420 μm, and occurs markedly in portal venules with diameters less than 70 μm in anesthetized rats.