Determination of plasma volume in swine by the enzyme-dilution method

Plasma volume of six young swine was determined by simultaneous dilution in the plasma of two purified porcine enzymes, aspartate aminotransferase (AST) and alanine aminotransferase (ALT), and Evans blue dye. Ninety-minute time-activity and time-concentration curves were obtained, and the dilution spaces of each plasma indicator at the time of injection were estimated by extrapolation of data from the first 30 min after injection. Plasma volumes estimated using the two enzymes agreed closely with each other (AST, mean 50.2 ml/kg; ALT, mean 49.8 ml/kg) and were 11% smaller than those determined using Evans blue dye (mean 56.3 ml/kg). Plasma volumes calculated from the AST and ALT activities and Evans blue dye concentration in a sample drawn 5 min after injection very closely approximated those obtained by extrapolation. These values were comparable to previously published estimates of plasma volume for swine of equivalent weight. Endogenous plasma levels of AST and ALT activity were measured in samples drawn from five swine before and after a 40% blood loss. No significant change in AST or ALT activities occurred after hemorrhage.