Hepatic microsomal composition studies in the Gunn rat.

The homozygous jaundiced (jj) Gunn rat exhibits hepatic microsomal enzyme activities which vary from markedly decreased to normal when compared with the non-jaundiced (JJ) Gunn rat. In order to determine if an alteration in microsomal lipid might be related to these observations, cholesterol, phospholipid, fatty acid and fluorescence polarization determinations were carried out in Gunn rats of both genotypes. Significant differences in microsomal palmitic, stearic and arachidonic acid composition were present, but these were not striking. Fluorescence polarization data best fit a two-phase linear model for both genotypes with no significant differences in breakpoint temperatures. In jj rats, the anisotrophy parameter ((r0/r)-1)-1 was significantly greater than that seen in JJ rats at both 25 and 37 degrees C, indicating a decreased membrane fluidity in the jaundiced animals. Alterations in enzyme microenvironment due to subtle changes in lipid composition may be related to the different enzyme activities observed in Gunn rats.