Cholesterol vehicle in experimental atherosclerosis. 23. Effects of specific synthetic triglycerides

Earlier work has shown that increasing concentration of palmitic acid at. t he sn-2 position of a fat enhances the atherogenic properties of that fat. This effect has been observed with lard, tallow, cottonseed oil, and palm o il. In the experiment reported here, we have studied the atherogenic effect s of four synthetic fats fed to rabbits as 58% (w/w) of the total fat (15%) (w/w) Of a semipurified diet containing 0.05% cholesterol. The fats being tested were: 1,3-stearoyl-2-oleoylglycerol (SOS);1,2-stearoyl-3-aleoylglyce rol (SSO); 1,3-palmitoyl- 2-oleoylglycerol (POP); and 1,2-palmitoyl-3-oleoy lglycerol (PPO). After 20 wk on diet there were no differences among the gr oups in weight gain, liver weight, serum, or liver lipids. These data are c onsistent with our previous findings. There were significant differences in atherosclerosis. The most severe atherosclerosis was observed in group PPO and the least in groups SSO and POP. Severity of atherosclerosis was grade d visually on a 0-4 scale. The average atherosclerosis [(aortic arch and th oracic aorta) divided by 2] was: SOS-1.35; SSO-0.97; POP-0.83; and PPO-1.80 . Fecal fat excretion (an indicator of fat absorption) was higher in the tw o groups fed the stearic acid-rich fats and lower in groups fed the palmiti c acid-rich fats. There were no differences in low density lipoprotein part icle size. The results confirm previous findings concerning the increased a therogenicity of fats bearing palmitic acid at the sn-2 position. The mecha nism underlying these observations is moot but may, in part, reflect greate r absorption of the atherogenic fat.