Abstract
We investigated the sex difference in stress-induced pressor responses and the effect of nitric oxide (NO) in free-moving adult rats. Male and female Wistar rats were implanted with radiotelemetry devices for blood pressure measurement. One week later, they underwent cage-switch stress for 30 min 24h after administration of plain tap water or NG-nitro- L-arginine methyl ester (L-NAME)-supplemented water (250μg/ml). In addition, another set of male and female rats were catheterized with cannulae into jugular veins. Blood samples were collected at rest and 30 min after the start of the stress for measuring plasma concentrations of norepinephrine (NE). In addition, we examined NOS expression and its phosphorylation in mesentery and lower limb muscle using Western blot analysis. Stress-induced pressure responses were attenuated significantly in the female compared with the male group and the difference disappeared after pretreatment of L-NAME. The resting level of plasma NE was higher in the female than the male group, but the stress-induced NE elevation was significantly higher in the male group. L-NAME pretreatment decreased NE levels at rest and during the stress in both groups and diminished the sex difference in the elevation of plasma NE. There was the sex difference in pressor responses to cage-switch stress in rats. The difference might be mediated by norepinephrine release from sympathetic nerve terminal through NO. [Jpn J Physiol 55 Suppl:S227 (2005)]
