The origin of chylomicron phosphatidylcholine in the rat

Abstract

This study investigates the pathways of origin of chylomicron phosphatidylcholine (PC) using a lymph- and bile-fistulated rat infused with a stabilized triolein emulsion. [14C-glycerol]PC was used to evaluate chylomicron PC generated by lyso PC acyltransferase. The percentage of chylomicron PC derived from the PC infused was directly proportional to the PC concentration in the infusate. When the infusate PC concentration was 10 mM, essentially all the chylomicron PC was derived therefrom at 4-6 h of infusion. Incorporation of the radiolabel was not found to be as great in the lymph subnatant PC as in chylomicron PC, suggesting that chylomicron and lymph subnatant PC might be supplied from different PC precursor pools. 32P(i) was infused into similarly prepared rats to judge chylomicron PC synthesized from de novo sources. In these experiments it was found that the percentage of chylomicron PC derived from de novo synthesis was inversely related to the PC concentration of the infusate. This suggests that exogenously infused PC inhibits de novo PC synthesis. When [32P]rat bile PC was infused with [14C glycerol]potato PC, the bile PC was preferred as a chylomicron precursor despite the greater similarity of the saturated fatty acids of potato PC to those of chylomicron PC. When the saturated fatty acids of bile and chylomicron PC were compared, chylomicron PC was significantly richer in stearate, suggesting extensive enterocyte modification of the saturated fatty acids of bile PC.