Differential distribution of orthophosphate-32P and glycerol-14C among molecular species of phosphatidylinositols of rat liver in vivo

The incorporation of orthophosphate-(32)P and glycerol-2-(14)C into the various species of rat liver phosphatidylinositols as a function of time was determined in vivo. (32)P was administered intraperitoneally and glycerol-(14)C was given intravenously. The phosphatidylinositols were resolved intact according to degree of unsaturation. 1-3 hr after injection of the labeled phosphate, the relative specific activity of the linoleoyl dienes exceeded that of the arachidonoyl tetraenes about 17-fold, and that of the trienes and polyenes about 8-fold. The relative specific activities of all the fractions became about equal 2-3 days after administration of (32)P. The labeling patterns obtained with glycerol were comparable to those seen for the phosphate. As early as 5 min about 65% of the activity was localized in the monoenes plus dienes, while only 17% was found in the tetraenes, although the mass proportions of these fractions were 7.1 and 77.0% of the total phosphatidylinositols, respectively. The recovery of the total radioactivity in the monoenes and dienes decreased continuously with time to about 15% at 9 hr, while that recovered in the tetraenes rose steadily to about 70%. The present data are consistent with an active synthesis of the monoenoic and dienoic phosphatidylinositols by way of the phosphatidate, followed by a deacylation-reacylation cycle involving arachidonic acid, as claimed for other rat liver glycerophosphatides.