Histomorphometric evaluation of intrahepatic changes following portal overflow in the rat.

Intrahepatic changes after an end-to-side renoportal arteriovenous shunt were studied in 60 rats. Portal and vena caval pressures did not increase from 3 weeks to 1 year. The number and diameters of the portal and hepatic vein lumens were determined through morphometric evaluation to calculate the relative areas. The proportion of area composed by the portal veins increased 3 weeks after shunt creation (P less than 0.001), reaching its highest level at 1 year (0.08% in control rats vs. 2.45% +/- 0.1% at 1 year). The proportionate area for hepatic veins also increased after 3 weeks (P less than 0.001), reaching its highest value by 12 weeks (0.49% in controls vs. 1.73% +/- 0.08% at 12 weeks). Our results suggest that there was a dramatic drop in the intrahepatic vascular resistance, especially at the portal bed, which may have compensated for the portal overflow. The theories regarding forward overflow compensatory mechanisms are discussed.