VITAMIN ENHANCES RELAXATION OF RAT AORTIC RINGS INDUCED BY K+ AND Mg2+

This study was designed to determine the effects of administration the effects of administration of vitamin C on the relaxation of vascular smooth muscle to K⁺ and Mg²⁺. The experiments were performed in two groups of Sprague-Dawley rats aged 6 weeks. Both control and test groups received rat chow and normal drinking water. In addition, the test group received vitamin C (100mg/kg/day) by intragastric administration for 8 weeks. At the end of this period aortic rings were obtained from both groups and used for isometric recordings. The relaxation responses to K⁺ and Mg²⁺ after precontraction with noradrenaline (10^-7M) were higher in the vitamin C-treated group compared with the control group. There was no difference in the relaxation responses to Mg²⁺ following K⁺ (40 mM) precontraction in the two groups. The enhanced relaxation to K⁺ in vitamin C rats suggests an increase in vascular Na+ -K⁺ ATPase activity. The increase in relaxation to Mg²⁺ follow NA precontraction, which was not observed with K⁺ precontraction, suggests that vitamin C enhances the mechanism of Mg²⁺-induced relaxation following receptor-mediated, but not depolarization-dependent contraction.