Mitochondrial membranes were isolated from the myocardium of young (4-month-old) 
and aged (33-month-old) male Long-Evans rats and compared in terms of 
cholesterol content and phospholipid and fatty acid composition. In aged rats, 
as compared to young, the major observations include: markedly higher 
cholesterol content; increased percentage of sphingomyelin and 
diphosphatidylglycerol (cardiolipin); in fatty acids, variable changes, with a 
predominant increase in the 16:0 in most phospholipids except cardiolipin, and 
sporadic increase in the longer chain (20:0, 24:0) fatty acids in cardiolipin; 
decreased unsaturation index for most phospholipids but increased for 
cardiolipin. These results are tentatively interpreted as indicative of an 
aging-related decrease in fluidity and energy transduction of mitochondrial 
membrane in the heart of aged rats and may be responsible, in part, for the 
decrements in cardiac function with aging.