Elevation of alkaline phosphatase by retinol in bovine endothelial cells and its possible relationship to lipid biosynthesis.

Alkaline phosphatase (EC 3.1.3.1) activity in bovine aortic endothelial cells in culture was stimulated in a synergistic manner by 10(-6) M retinol and by 10(-7) M dexamethasone. An early exposure to retinol was required for maximum stimulation and could be reproduced by the addition, during growth, of 2 micrograms/ml compactin. The induced enzyme activity in cell lysates prepared from cells treated with retinol and dexamethasone had a Vmax that was 50-fold that of the controls. The stimulatory effect of retinol could be partially reversed by the addition of sonic dispersions made from cholesterol and phosphatidylcholine. The incorporation of [14C]acetate into saponifiable and non-saponifiable cellular lipids was inhibited by 10(-6) M retinol but the activities of 3-hydroxy-3-methylglutaryl coenzyme A reductase (EC 1.1.1.34) and 3-hydroxy-3-methylglutaryl coenzyme A synthase (EC 4.1.3.5) remained unaffected. The results suggest that retinol might inhibit lipid biosynthesis through an alternate mechanism.