Lipid content and lipoprotein lipase activity in skeletal muscle of lactating and weaned rats.

The aim of the investigation was to study the changes in lipid content and lipoprotein lipase (LPL) activity of skeletal muscle of lactating and weaned rats, in order to gain insight on the role of skeletal muscle in the metabolism of triacylglycerols not used by the mammary gland after weaning. Sprague-Dawley rats fed ad libitum were killed 0, 8, 12, and 24 h after litter separation on the 14th day of lactation. Electron microscopy, as well as determinations of the total fat and phospholipid content were performed on muscles of the right hind limb. Lipoprotein lipase activity was determined in extracts of acetone powder of skeletal muscle, mammary gland, and adipose tissue using dibutyryl fluorescine as substrate. Fat droplets were identified in the muscle interfiber spaces of weaning rats. Muscle total fat and phospholipids were higher in weaned than in lactating rats. After litter separation, lipoprotein lipase activity increased significantly in muscle and in adipose tissue (fourfold), while activity in the mammary gland decreased. The increased muscle lipoprotein lipase activity in the weaned rats seems to be associated with the higher content of fat and with the presence of fat droplets.