Cyclopropenoid fatty acids (CPFA), which are a group of fatty acids produced by plants of the order Malvales, are known to induce adverse physiological effects when administered to a variety of animal species. A structurally strained cyclopropene ring is present in all CPFA and is believed responsible for the toxic action of these fatty acids. Dietary consumption of CPFA by mammals, poultry and fish has resulted in toxic responses including hepatic damage, impaired reproductive capabilities and sizeable alterations in lipid metabolism. Furthermore, CPFA have been identified as mildly carcinogenic and strongly cocarcinogenic towards rainbow trout (Salmo gairdneri). The mechanism by which CPFA enhance carcinogenesis is currently not understood. The research in this thesis has therefore been directed toward obtaining a better understanding as to how CPFA induce toxic responses in rainbow trout. Hepatic plasma membranes were isolated from both control trout and trout which had consumed dietary CPFA. The plasma membranes were then compared via the use of electron microscopy, chromatographic analysis of phospholipid and fatty acid content, two dimensional polyacrylamide gel electrophoresis of proteins, and Western blot analysis of concanavalin A sensitive glycoproteins. Electron micrographs revealed that control plasma membranes appeared more homogeneous than CPFA membranes and were characterized by more membrane sheets and less vesicularization. The analysis of enzyme activities revealed that CPFA caused a decrease in whole liver glucose-6-phosphatase activity and that control plasma membranes expressed slightly higher glucose-6-phosphatase and 5'-nucleotidase activities as compared to CPFA membranes. Although dietary CPFA appeared to have no effect on the phospholipid content of the plasma membranes, significant alterations in the fatty acid profiles of ethanolamine and choline phospholipids were observed. CPFA caused a decrease in palmitic, palmitoleic and oleic acids while the level of stearic and docosahexaenoic acids subsequently increased. Differences between the protein content of control and CPFA plasma membranes were made clear through the analysis of electrophoretic and Western blotting data. Membranes isolated from fish fed CPFA contained several proteins of high molecular weight (above 66,000 daltons) and other proteins of high isoelectric point that were not present in control plasma membranes. Additionally, two families of glycoproteins which had previously been identified as microsomal in origin were detected only in CPFA plasma membranes. A discussion concerning the possible causes and biological ramifications of the observed subcellular alterations caused by CPFA insult is also presented in this thesis. / Graduation date: 1989