VITAMIN-E RESTORES ENDOTHELIUM-DEPENDENT VASODILATATION IN CHOLESTEROL-FED RABBITS - IN-VIVO MEASUREMENTS BY PHOTOPLETHYSMOGRAPHY

Objective: Pulse curve plethysmography was used to examine the effect of vitamin E on endothelium dependent and independent vasodilatation i n unanaesthetised cholesterol fed rabbits in vivo. The height of the d icrotic notch was used as an index of general arterial vasodilatation. Methods: Twenty eight rabbits were divided into three study groups; a control group (group 1, n = 8), a group fed 1% cholesterol (group 2, n = 10), and a group fed 1% cholesterol with the addition of 0.2% vita min E after four weeks (group 3, n = 10). After six weeks on diet the vasodilator responses to acetylcholine and glyceryl trinitrate were me asured by photoplethysmography of the rabbit ear. Recordings were made during light sedation at baseline and during infusion of acetylcholin e (1.5, 3.0, 6.0, and 12 mu g.min(-1)) and glyceryl trinitrate (3.75, 7.5, and 15.0 mu g.min(-1)). In a second set of experiments with contr ol fed rabbits (n = 5), acetylcholine infusions were given before and after infusion of L-nitro-arginine (15 mg). Results: The relative heig ht of the dicrotic notch (which predominantly indicates arterial tone in the larger vessels) was reduced by acetylcholine in a dose dependen t manner, but in cholesterol fed rabbits (group 2) this response was s ignificantly decreased. Rabbits receiving concomitant dietary vitamin E responded in a similar manner to controls. The difference was most p rominent using acetylcholine at a dose of 3.0 mu g.min(-1), where the mean change from baseline was 11(SEM 4)% in group 2, compared to 31(6) % in group 1 (p = 0.01), and to 26(5)% in group 3 (p = 0.02). Similar differences between the groups were observed for the increase in heart rate during acetylcholine infusions. In contrast, the responses to gl yceryl trinitrate were similar in all groups. After infusions of L-nit ro-arginine, the responses to acetylcholine were blunted. Conclusions: Supplementation with vitamin E restored the otherwise reduced vascula r response to acetylcholine in cholesterol fed rabbits. Analysis of ph otoplethysmographic pulse curves is a simle non-invasive method of eva luating arterial vasodilator effects. However, the nature of the measu red dilator response needs to be characterised further.