Submitted on December 26, 2002
Accepted on August 21, 2003
Effects of hematocrit and norepinephrine on segmental vascular resistance distribution in isolated perfused rat livers
CHIAKI KAMIKADO1, TOSHISHIGE SHIBAMOTO2*, MINORU HONGO3, and SHOZO KOYAMA1
1 Department of Physiology, Division 2, Shinshu University School of Medicine, Matsumoto, Nagano, Japan
2 Department of Physiology, Division 2, Kanazawa Medical University, Uchinada, Ishikawa, Japan
3 Department of Cardiovascular Medicine, Shinshu University School of Health Sciences, Matsumoto, Nagano, Japan
* To whom correspondence should be addressed. E-mail: shibamo{at}kanazawa-med.ac.jp.
We studied effects of blood hematocrit (Hct), blood flow or norepinephrine on segmental vascular resistances in isolated portally perfused rat livers. Portal-hepatic venous resistance (Rt) was assigned to the portal (Rpv), sinusoidal (Rsinus) and hepatic venous (Rhv) resistances using the portal occlusion (Ppo) and the hepatic venous occlusion (Phvo) pressure, that were obtained during occlusion of the respective line. Four levels of Hct, 30%, 20%, 10% and 0% were studied. Rpv comprises 44% of Rt, and Rsinus 37%, and Rhv 19% in livers perfused at Hct 30% and Ppv of 9.1 cmH2O. As Hct increased at a given blood flow, all three segmental vascular resistances of Rpv, Rsinus, and Rhv increased at flow higher than 15 ml/min-1. As blood flow increased at a given Hct, only Rsinus increased without changes in Rpv or Rhv. Norepinephrine increased predominantly Rpv and, to a smaller extent, Rsinus, but it did not affect Rhv. Finally, we estimated Ppo and Phvo from the double occlusion maneuver, which occluded simultaneously both the portal and hepatic venous lines. The regression line analysis revealed that Ppo and Phvo were identical with those measured by double occlusion. In conclusion, changes in blood Hct affect all three segmental vascular resistances, while changes in blood flow affect Rsinus, but not Rpv or Rhv. Norepinephrine increases mainly presinusoidal resistance. Ppo and Phvo can be obtained by the double occlusion method in isolated perfused rat livers.
