Angioscopic evaluation of the effect of estrogen on ovariectomized Japanese monkeys

Using angioscopy to study the atheroprotective effect of estrogen, atherosclerotic changes in surgically postmenopausal Japanese monkeys were observed for a long period. Changes in serum lipids and estradiol were also followed. About 3-6 months after the 2% cholesterol diet, serum cholesterol increased up to three times normal value, and atheroma was first found at the orifice of major branches of the abdominal aorta. However, in the other group of 2% cholesterol including an oral estrogen diet, the appearance of atheroma was inhibited until 12 months, although serum cholesterol increased gradually. The chronologic investigation was continued over 3 years. From these results we concluded that the most important atheroprotective effect of estrogen is the direct inhibition of atherosclerosis in the arterial wall, and improvement in lipid metabolism is of secondary importance.