Alterations of cell membrane composition during prolonged fasting in lizards.

Male lizards fasted for 35 days showed significant alterations in the lipid composition of membranes isolated from a variety of organs and tissues. Unesterified cholesterol was significantly increased in membranes from kidney, skeletal muscle, small intestine, testis and heart but not in those from lung, brain and liver; cholesterol/phospholipid molar ratio was also significantly increased in membranes from all organs except brain and liver. Membrane total phospholipids were reduced for all tissues except brain and liver, whilst significant reductions in the molar ratio of membrane phosphatidylcholine to sphingomyelin occurred in kidney, muscle, testis, intestine and liver. Similar alterations in lipid composition were found in plasma and significant correlations between plasma and membrane cholesterol/phospholipid and phosphatidylcholine/sphingomyelin molar ratios were found for those organs in which significant lipid changes occurred during fasting. Lizards fasted for 35 days and then refed a natural diet, such that they started to regain weight, had normal membrane lipid compositions. These observations suggest that during prolonged fasting certain tissues of the lizard are unable to maintain a normal membrane lipid composition and that abnormal plasma lipoproteins may be involved in this process.