Biosynthesis and turnover of individual molecular species of phosphatidylcholine in liver and bile.

The individual molecular species of rat liver diacylglycerol and phosphatidylcholine, and bile phosphatidylcholine were analyzed and the metabolism of the individual molecular species of liver and bile phosphatidylcholines was studied using bile fistual rats. 1. Bile phosphatidylcholine contained more palmitoyl-linoleoyl, and less stearoyl-linoeoyl and stearoyl-arachidonyl species than liver phosphatidylcholine. 2. More rapid incorporation of [2-(3H)]glycerol into palmitoyl-oleoyl and palmitoyl-linoleoyl species of phosphatidylcholine in bile as compared with that in the liver was found. This result seems to support the concept that a specific subpool, termed a dynamic pool, of phosphatidylcholine in the liver appears to serve for bile phosphatidylcholine. 3. When 1-[9,10-(3H)]palmitoyl- and 1-[1-(14C)]stearoyl-glycero-3-phosphocholines were injected intraportally, the specific activity of palmitoyl species of bile phosphatidylcholine exceeded that of liver phosphatidylcholine at 60 min after the injection, while that of stearoyl species in bile was still significantly lower than that in the liver. This result supports the idea that there is a specific mechanism concerning the preferential secretion of palmitoyl species into bile. 4. It was noted that liver phosphatidylcholine species in the dynamic pool have the same specific activity as that of bile phosphatidylcholine, and the size of the dynamic pool is about 5% of the total liver phosphatidylcholine. The turnover rate of palmitoyl-linoleoyl phosphatidylcholine in the dynamic pool was very rapid, and was almost the same as the formation rate of the phosphatidylcholine species from the corresponding species of diacylglycerol.