Hydrogen Peroxide-Induced Inhibition of Vasomotor Activity: Evaluation of Single and Combined Treatments With Vitamin A and Insulin in Streptozotocin-Diabetic Rats

摘要

A positive correlation has been established between increased oxidative stress and cardiovascular diseases in diabetes mellitus. We evaluated the effects of single or combined treatments with vitamin A (retinol acetate, 30 mg/kg/day, for 12-weeks) and insulin (8-10 IU/rat/day for the final 6-week) on vasomotor activity, oxidative stress and retinol metabolism in 12-week streptozotocin diabetic rats. The vasomotor activity was determined by measuring in vitro responsiveness of aorta rings to phenylephrine (PE) and acetylcholine (ACh) in the absence or in the presence of hydrogen peroxide (H2O2). Preincubation with H2O2 (10 μM) produced a significant decrease in PE (1 mM)-induced contraction in untreated-diabetic but not in control rats. Single treatment withinsulin counteracted this effect of H2O2 andalso reversed the increased contractile responseof diabetic aorta to PE, while vitamin A wasfound to be ineffective. H2O2 (10 μM) alsoinhibited ACh (1 mM)-stimulated endothelium-dependent relaxation two fold more in diabeticthan in control aorta. In the prevention ofH2O2-induced inhibition of vascular relaxationto ACh, vitamin A alone was markedly effectivewhile insulin alone was not. The combinationof vitamin A plus insulin removed theinhibitory action of H2O2 in diabetic aorta.Diabetic animals displayed an increased level of aorta thiobarbituric acid reactive substance(TBARS) in association with decreased levels ofplasma retinol and retinol-binding protein(RBP). Single treatment with insulin, in spite ofallowing recovery of normal growth rate andimproved glucose and retinol metabolism indiabetic rats, was unable to control TBARSproduction to the same extent as vitamin Aalone. Our findings suggest that the maintenanceof ACh-stimulated endothelium-dependentvasorelaxant tone in normal physiologicallevels depends largely on the prevention and/orinhibition of peroxidative stress, which isachieved by combined treatment with vitaminA plus insulin. The use of vitamin A togetherwith insulin provides a better metabolic controland more benefits than use of insulin alone inthe reduction of diabetes-induced vascularcomplications.