Phospholipases in arterial tissue. VI. The role of growth and age in the development of phosphatide acyl-hydrolase activity in aortic tissue

Age-dependency of vascular phospholipid deacylation-reacylation in spontaneously hypertensive rats

We have studied the temporal relation of phospholipid turnover and prostaglandin synthesis to the evolution of hypertensive vascular disease in the spontaneously hypertensive rat. The incorporation of arachidonate into aortic phospholipids, its release by phospholipase A2 and its utilization for prostaglandin synthesis were compared in spontaneously hypertensive and Wistar-Kyoto rats aged 7, 20 and 42 weeks. When expressed per mg of protein in the assay medium, arachidonate incorporation into aortic phospholipids decreased, while prostaglandin synthesis increased, with age in both rat strains. No significant differences were noted between hypertensive and normotensive animals at 7 weeks of age whereas both enhanced phospholipid turnover and prostaglandin synthesis was demonstrated in hypertensive rats at 20 and 42 weeks of age. The higher phospholipase activity in hypertensive aortas was associated with a significant increase in the capacity for exogenous lysophosphatide hydrolysis. Transacylation and reacylation of lysolecithin, however, were not significantly enhanced in hypertensive aortas. These biochemical changes accompany, and may be related to, structural modifications of the aortic wall in the course of hypertension.

Turnover of phospholipids in rat aortic smooth muscle cells in culture

Smooth muscle cells derived from rat aortic media were explanted and grown in culture for 14 to 60 days. During that time they formed a confluent multilayer and depostied extracellular material resembling newly formed elastin. The lipid composition of the cells in culture differed slightly from the parent cells in the intact aorta with respect to a higher phospholipid/DNA ratio and a higher lecithin content. The cholesterol content resembled that of parent cells. After incubation with labeled precursor the cultured cells show an active lipid synthesis; choline is incorporated mainly into lecithin, whereas glycerol and palmitate appear in phospholipids and to a lesser extent in neutral lipids. After a 2 hour pulse and up to 96 hour chase there is a linear fall in the specific acitivty of lecithin with a half-time of 28 to 30 hours. The rate of fall in specific activity of glycerol- or choline-labeled lecithin was found to be similar, indicating that choline does not turn over by an exchange reaction and is a suitable marker for studying phospholipid turnover in cultured cells. The results provide a basis for investigation of the effect of increasing cellular cholesterol content on phospholipid turnover.