Isolated liver perfusion is a useful technique for the study of a variety of metabolic functions of the liver (Bartosek, Guaitani and Miller, 1973). The composition of the perfusate varies from laboratory to laboratory, but the one which is most widely used contains erythrocytes suspended in a plasma substitute, such as Krebs-Henseleit solution (Krebs and Henseleit, 1932), which may be supplemented vvath albumin and organic nutrients. Studies in our laboratory, using a perfusate such as this, have led to an examination of the [HCO.^'] of Krebs-Henseleit solution. We have found that the nominal [HCO3'] of Krebs-Henseleit, which is designed to approximate rat plasma, is inconsistent with the [HGOg'] measurable in this artificial physiological medium.Solutions prepared according to the formula of Krebs-Henseleit (Table 1) were gassed with carbogen of appropriate O2/CO2 content and analysed for [HCO3'] using the following four methods:

Summary. Alanine aminotransferase (ALT) activity in rat plasma was stable for up to 56 days when stored at -25°. High activity plasma samples were less stable. ALT activity was markedly unstable when derived from isolated hepatocyte preparations, and declined to 8-16% of initial values after 28-56 days storage at -25°.