Ribosome structure and chylomicron formation in rat intestinal mucosa

Sucrose gradient sedimentation and electron micrographic studies were made on the ribosomes of the cells of intestinal mucosa isolated from control, bile fistula, and puromycin-treated rats. In comparison to controls, there was a 40 to 60 per cent decrease in polysome content of the cells following administration of puromycin or deprivation of luminal choline by creation of a bile fistula. Feeding of lysolecithin of choline to the bile fistula rats or addition to the isolated cells in vitro resulted in a complete restoration of the polysome profile along with lipprotein synthesis and chylomicron release. Addition of lysolecithin to isolated cells treated with puromycin in vitro also brought about a reaggregation of the ribosomes and a reactivation of phospholipid biosynthesis. Choline had no detectable effect on phospholipid synthesis or ribsosme aggregation when fed to ppuromycin-treated rats or when added to puromycin-treated cells in vitro. The results suggest that chylomicron formation and the release by the muscosal cells depend upon intact rough endoplasmic reticulum and an active protein adn phospholipid biosynthesis. The role of lysolecithin in this process is ratonalized on the basis of its ability to supply a precursor of lecithin as well as a surfactant which affects the aggregation, or membrane rebinding of ribosomes, or both.