VITAMIN-C REDUCES CHOLESTEROL-INDUCED MICROCIRCULATORY CHANGES IN RABBITS

The microcirculation was studied for 10 weeks in untreated rabbits (n= 12) and in rabbits treated with vitamin C in their drinking water (0.5 g/d, n=6), a 1% cholesterol diet (n=12), or a combination of the two treatments (n=11). The studies were performed by direct intravital mic roscopic imaging of the conjunctiva of both eves to evaluate blood flo w velocity, microvessel diameter, and microhemorheologic conditions. A s we reported previously, changes occurred in all of the aforementione d variables as a consequence of cholesterol feeding. After 3 and 6 wee ks of feeding, there was a marked and significant (P<.0001) decrease i n blood flow velocity in third-order arterioles. which was accompanied by stasis and erythrocyte aggregation in the smaller conjunctival ves sels. When cholesterol treatment was combined with vitamin C, blood fl ow was almost identical to that of controls and significantly (P<.0001 ) higher than that of rabbits treated with cholesterol alone. All othe r changes were also significantly reduced by the addition of vitamin C treatment to the cholesterol diet. Cholesterol-treated rabdeveloped m acroscopic arterial lesions that were not significantly reduced by vit amin C treatment. Neither circulating oxysterol levels nor atheromas w ere reduced by vitamin C treatment, which also had no significant effe ct on lipid or circulating vitamin E levels. We have previously shown that the lipid-soluble antioxidant BHT is able to prevent both cholest erol-induced microcirculatory changes and the development of arterial lesions in rabbits. This phenomenon is compatible with a critical oxid ation step occurring in the lipid phase that is common to both process es. The finding that microcirculatory changes can be prevented by a wa ter-soluble antioxidant is compatible with a role for water-soluble ox idants in this context. The possibility is discussed that vitamin C mi ght also be important for the microcirculation in humans.