Potential Role for Oxidative Stress in 2,2′-Dichlorobiphenyl–Induced Inhibition of Uterine Contractions but not Myometrial Gap Junctions

Abstract

Previously, we reported that 2,2'-dichlorobiphenyl (2,2'-DCB)-induced decreases of amplitude and synchronization of uterine contractions are dependent on MAPK-induced phosphorylation of Connexin43 (Cx43) and inhibition of myometrial gap junctions. Recent studies show that oxidative stress inhibits uterine contractions and myometrial gap junctions also. The present study examines the hypothesis that 2,2'-DCB-induced modification of uterine contraction is dependent on oxidative stress-mediated inhibition of myometrial gap junctions via activation of mitogen-activated protein kinase (MAPK) and phosphorylation of Cx43. In uterine strips treated with alpha-tocopherol (100 microM), deferoxamine mesylate (Def, 50 microM), or superoxide dismutase (SOD, 1000 U) after a 1-h exposure to 100 microM 2,2'-DCB, modification of uterine contractions reversed 1 h after initiating antioxidant treatment. Treatment of uterine strips with 100 microM 2,2'-DCB for 1 h lowered total SOD activity and also induced a surge of superoxide generation after 5 min of exposure. However, myometrial cells exposed in culture to 100 microM 2,2'-DCB did not produce reactive oxygen species as determined by the lack of superoxide anion generation measured by the cytochrome c reduction assay, reactive species by the formazan assay, hydrogen peroxide by the 2',7'-dichlorofluorescein assay, and lipid peroxidation by the thiobarbituric acid-reactive substance assay. Furthermore, cotreatment with SOD or Def was unable to prevent 2,2'-DCB-induced phosphorylation of Cx43, activation of MAPK, and inhibition of myometrial gap junctions. Although antioxidants reversed 2,2'-DCB-induced inhibition of uterine contraction force and synchronization, the myometrial cell culture experiments failed to support oxidative stress as a mechanistic link between 2,2'-DCB-induced inhibition of myometrial gap junctions and modification of uterine contraction.