Gender Differences in Myogenic Tone in the Superoxide Dismutase Knockout Mouse: An Animal Model of Oxidative stress

Oxidative stress mediated by pro-oxidants has been implicated in the pathogenesis of vascular disorders. However, the effect of pro-oxidants on myogenic regulation of vascular function and the differential influence of gender is not known. Superoxide dismutase (SOD), an intracellular enzyme restricts excess pro-oxidant levels and may limit vascular dysfunction. We therefore tested the effects of CuZnSOD deficiency on vascular tone in both male and female SOD knockout mice (SOD-/-). We hypothesized that myogenic tone would be enhanced in SOD-/due to excess pro-oxidants compared to wild-type control mice. Indeed, resistance-sized mesenteric arteries from SOD-/mice exhibited enhanced myogenic tone compared to controls. Myogenic tone was lower in females compared to males in control mice. Interestingly, this gender effect was absent in SOD-/mice such that myogenic tone of mesenteric arteries from females was equated to that of arteries from males. Furthermore, the pathways that modulate myogenic tone were diverse. In both male and female controls, inhibition of prostaglandin H synthase (PGHS) and nitric oxide synthase (NOS) pathways enhanced myogenic tone. In female SOD-/mice, inhibition of PGHS and NOS pathways enhanced myogenic tone to a greater extent compared to controls. Conversely, in male SOD-/-, NOS and PGHS inhibition did not alter tone, and only inhibition of gap junctions enhanced myogenic tone. In conclusion, this study revealed enhanced myogenic tone in SOD-/mice compared to controls. Furthermore, CuZnSOD deficiency particularly enhanced myogenic tone in females such that their vascular tone attained the level of male SOD-/mice, possibly mediated by pro-oxidants.