Metabolism of lysolecith1n in vivo and in vitro with particular emphasis on the arterial wall

Abstract

Lysolecithin labeled with [Me- 3H]choline and [I- 14C]palmitate was injected intravenously into squirrel monkeys or was incubated with aortas of squirrel monkeys or rabbits in vitro. Injected lysolecithin rapidly appeared in all tissues where it was acylated or hydrolyzed. In most tissues 3H : 14C ratios in lysolecithin and lecithin were the same as those for the injected lysolecithin. Nevertheless some labeled palmitate was found in position 2 of lecithin. In many tissues the ratio of 3H in water-soluble constituents (glycerophosphorylcholine, phosphorylcholine, choline, and betaine) to 14C in free fatty acids and glycerides was the same as that for injected lysolecithin. In the aorta wall, plasma, skeletal, and cardiac muscle there were very low ratios due to the absence of water-soluble 3H. When pieces of squirrel monkey aorta were incubated with labeled lysolecithin, radioactivity was present in lysolecithin, lecithin, and free fatty acids of the tissue and incubation medium, but water-soluble 3H (mostly glycerophosphorylcholine) was only in the incubation medium. The presence of atherosclerosis had a profound effect on the pre- and postincubation levels and on net uptake of lysolecithin in the intima plus inner media but not in the outer media. Incubation in a mmdium free of lysolecithin resulted in a slight fall in lysolecithin concentrations in the aorta. Lysolecithin was fairly uniformly distributed in subfractions of homogenates of atherosclerotic intima plus inner media but was most prevalent in the plasma membrane and 13 · 10 7 × g . min supernatant fractions.