Lipoprotein lipase and uptake of triacylglycerol, cholesterol and phosphatidylcholine from chylomicrons by mammary and adipose tissue of lactating rats in vivo.

The relationship between lipoprotein lipase activity and uptake of triacylglycerol, cholesterol and phosphatidylcholine from chylomicrons was studied in mammary gland and adipose tissue of rats lactating 6--7 days. 60% of triacylglycerol [14C]oleic acid, 13% of [3H]cholesterol and 8% of [32P]phosphatidylcholine in chylomicrons injected intravenously were taken up within 11 min by mammary gland whereas negligible amounts were taken up by adipose tissue. Non-suckling for 44 h decreased markedly uptake of all lipids by mammary gland and retarded clearance of chylomicrons from blood, while it increased significantly uptake of triacylglycerol fatty acids and cholesterol by adipose tissue. Non-suckling also decreased lipoprotein lipase activity in mammary gland from 7.7 to 0.4 units/g, while it increased activity in adipose tissue from 0.1 to 2.7 units/g. These findings indicate that lipoprotein lipase is involved in uptake of chylomicron triacyglycerol and cholesterol by mammary gland and adipose tissue, and also in uptake of chylomicron phosphatidylcholine by mammary gland. They also show that reciprocal changes in lipoprotein lipase activity in mammary gland and adipose tissue, as occur during lactation, result in diversion of chylomicron lipids from one tissue to the other.