PHOSPHOLIPASES IN ARTERIAL TISSUE .3. PHOSPHATIDE ACYL-HYDROLASE LYSOPHOSPHATIDE ACYL-HYDROLASE AND SPHINGOMYELIN CHOLINE PHOSPHOHYDROLASE IN RAT AND RABBIT AORTA IN DIFFERENT AGE GROUPS

Aortae of rats and rabbits 1-24 months of age were examined for phospholipid content and the activity of different phospholipases. In both species there was a fall in DNA content per wet weight and a rise in the phospholipid to DNA ratio with age. Out of the total phospholipids, sphingomyelin showed the highest increase, and in the rabbit there was also a rise in lecithin. The various phospholipases investigated in aortic homogenates displayed a behaviour which varied with age. In both species there was no change in sphingomyelinase (sphingomyelin cholinephosphohydrolase) activity, a slight increase in lysolecithinase (lysolecithin acyl-hydrolase, EC 3.1.1.5) and a remarkable rise in the phosphatide acyl-hydrolase (phospholipase A, EC 3.1.1.4). In the rat the rise in phosphatide acyl-hydrolase is much more marked than in the rabbit aorta. Incorporation of labelled choline into lecithin and sphingomyelin by rat and rabbit whole aortae in vitro was increased with age. The following chain of events for the ageing rat aorta was postulated: the increase in phosphatide acylhydrolase activity, which follows the rise in phospholipid synthesis, prevents the accretion of lecithin, while the lack of increase in sphingomyelinase activity results in a rise in cellular sphingomyelin. The possible correlation between the biochemical, enzymic and morphological changes occurring during ageing of aortic medial cells is discussed. © 1969.