Enhanced turnover of phosphatidylcholine in platelets of hypertensive rats. Possible involvement of a phosphatidylcholine-specific phospholipase C.

In an attempt to determine the mechanism involved in the hyperreactivity of platelets in primary hypertension, the dynamic behavior of phospholipids was investigated in quiescent platelets of spontaneously hypertensive rats (SHR) compared to normotensive controls. By using 32Pi, [methyl-3H]choline or [3H]glycerol as the radioactive precursors, the labeling of phosphatidylcholine (PC) was shown to be markedly enhanced (10-20-times) in SHR compared to controls. This difference between SHR and controls could not be ascribed to differences either in the actual amount of PC or in the uptake of various labels, suggesting that PC turnover was markedly enhanced in platelets of SHR. The [methyl-3H]choline labeling of phosphocholine and of CDP-choline was twice as high in SHR as in controls; chase experiments showed that when the label disappeared from phosphocholine, it was rapidly converted to PC. The results indicated that in rat platelets, PC synthesis occurred mainly via the CDP-choline pathway, and suggested that CTP:phosphocholine cytidylyltransferase was the rate-limiting step; they also indicated that the activity of this enzyme and that of choline kinase might be enhanced in SHR platelets compared to Wistar-Kyoto rat (WKY) platelets, and may thus be responsible for the enhanced PC synthesis. From these results, the existence of a PC-specific phospholipase C activity involved in PC turnover in SHR platelets can be envisaged.