Effect of increasing doses of angiotensin II infused into normal and hypertensive Wistar rats on low density lipoprotein and fibrinogen uptake by aortic walls.

The effect of 6 days' s.c. infusions of angiotensin II at increasing doses was determined on the uptake of rat or human low density lipoprotein (LDL) and of human fibrinogen by aorta in normal and spontaneously hypertensive rats. Rat or human LDL or human fibrinogen was injected i.v. 5 days after the start of infusion, and 24 hr later the radioactivity of aortic walls was determined. Body weight was almost constant in control rats and moderately decreased in a dose-dependent way by angiotensin II. Diastolic blood pressure decreased slightly over 6 days in control rats and increased transiently at the lowest dose of angiotensin II and progressively with two higher concentrations. All three angiotensin II concentrations significantly increased the uptake of rat and human LDL and of fibrinogen by aorta. The increase was dose related for rat LDL but not for human LDL or fibrinogen. In spontaneously hypertensive rats of the same age in which blood pressure was higher than in angiotensin II-infused rats, protein uptakes were not increased. The blood content of aortic walls was negligible and not altered by angiotensin II. Therefore, the uptake of atherogenic plasma proteins by rat aorta is increased by angiotensin II, but this effect may be independent of its pressor action.