Effects of Peroxyl Radicals on Contractility of Rabbit Aorta and Guinea Pig Atria

Background: High-fat meals may lead to hypotension, oxidative stress and increases of lipopolysaccharide (LPS). Contrasting results have been reported after treatment of isolated tissues with hydrogen peroxide and LPS, whereas the effects of peroxyl radicals, involved in the propagation reaction of lipoperoxidation, have not been investigated previously. Aim: In the present study, we aimed to evaluate the effects of peroxyl radicals on the contractile responses in isolated rabbit aorta and guinea pig atria. Methods and Results: We treated isolated guinea pig atria, rabbit aorta strips and rings with 2,2'-Azobis (2- amidinopropane) dihydrochloride (AAPH). AAPH did not affect isoprenaline-induced contraction in guinea pig atria, whilst it dose-dependently reduced the contractile responses induced in rabbit aorta strips by cumulative doses of adrenaline (ADR) and induced an endothelium-independent relaxation of noradrenaline (NA)-contracted aorta rings. The effects of KCl-induced and BaCl2-induced contractions were small. Furthermore, alkalinization with NH4Cl of NAcontracted aorta rings significantly reduced the vasodilatatory activity of AAPH. Conclusion: The present study suggests that peroxyl radicals induce acute functional alterations on vascular contraction through intracellular pH regulation. This finding could be related to the documented after meal increase in oxidative burst and endotoxin and the related hypotension.