Human erythrocytes are not suitable for determination of intravascular volume of perfused rat liver.

Homologous or heterologous erythrocytes have been widely used for the estimation of intravascular volume of the liver. However, cross-species blood mediates immune response in the organ, and foreign cells are rapidly cleared from the plasma, indicating that heterologous erythrocytes may not be a suitable marker for determination of vascular space. This aspect was investigated in the perfused rat liver preparation following bolus administration of human (heterologous) erythrocytes into the portal vein. To compare the extent of its distribution within the liver, rat (homologous) erythrocytes and Evans blue were chosen as the reference vascular and extracellular markers, respectively. Hepatic distribution of human erythrocytes was influenced by the perfusion medium (with and without protein) and injection number (first and second injections). Mean transit time and hence volume of distribution decreased in the presence of protein and repetition of the injection. Even in the presence of protein, the volume of distribution obtained for human erythrocytes was larger than that of the extracellular volume of the liver obtained with Evans blue (0.22 +/- 0.01 vs. 0.20 +/- 0.02 ml/g), indicating that they are not suitable for determination of intravascular volume of the perfused rat liver preparation.

Potential use of freeze-drying technique for estimation of tissue water content.

Desiccation and freeze-drying methods were used for the estimation of water content of various rat tissues. In the desiccation method, the tissue samples were cut into small pieces and subsequently dried at 40 degrees C to constant weight. In the freeze-drying method, the prefrozen tissue samples were freeze-dried (-50 degrees C) for 24 h. Tissue water contents obtained by the desiccation and freeze-drying methods were very similar, with no significant difference between them. Regardless of the method, the highest tissue water content was found in testes (0.841 +/- 0.010 ml/g for freeze-drying and 0.865 +/- 0.002 ml/g for desiccation); the lowest values were obtained in bone (0.254 +/- 0.007 ml/g for freeze-drying and 0.267 +/- 0.003 ml/g for desiccation). Upon correction for the water content of residual tissue blood, regardless of the drying method, significant differences were found between corrected and uncorrected tissue water values of all tissues. However, for a given method, the difference between the tissue water contents was not significant after correcting for residual blood. The water content values for all tissues (except bone) agree well with those published previously and obtained by desiccation. All these clearly suggest that the freeze-drying method can be used as an alternative to desiccation for estimation of tissue water content.