β Estrogen knock out receptor mice (βERKO) have recently been shown to be hypertensive and to have altered contractile function in the aorta (Zhu et al. 2002). Since estrogens have also been implicated in vascular compliance and structure, we have evaluated distensibility and permeability of small mesenteric arteries from male and female βERKO mice and their wild-type littermates.
Male and female βERKO mice and their wild-type littermates were humanely killed by a rising concentration of CO2 and cervical dislocation. Small mesenteric arteries (~185 mm in diameter) were rapidly dissected and mounted on a pressure myograph (Living Systems Instrumentation Inc, USA). Passive distensibility curves were constructed by carrying out stepwise increments in intraluminal pressure (20-100 mmHg) in a calcium free medium and by measurement of lumen diameter. In separate arteries permeability was assessed by infusion of Evans blue dye (0.03 %) into the vessel lumen and pressure maintained at 60 mmHg whilst photographic images were obtained every min for a five min period. Evans blue staining was evaluated on the basis of blue colour distribution within the artery wall. The degree of permeability was calculated in a blinded manner by two independent investigators using an ordered scale from 0 to 3+.
Passive distensibility was similar between mesenteric small arteries from βERKO males and wild-type littermates (n = 8 in each group). However arteries from female βERKO mice were less distensible than those of wild-type female littermates (n = 8 in both groups, P = 0.011 by ANOVA). No differences in permeability were apparent between arteries from βERKO females and wild-type female littermates whereas arteries from βERKO male mice were more permeable than those of male wild-type littermates (arbitrary units, values are median (confidence intervals) 2.5 (0.66-3) n = 8 vs. 1(0-1) n = 7, P = 0.014; Mann-Whitney test).
In conclusion, this study suggests that the estrogen receptor β (ERβ) has gender specific effects on distensibility and permeability in small mesenteric arteries of the mouse. Estrogens, through the ERβ may increase distensibility and hence vascular compliance in the resistance vasculature of the wild-type female mouse whereas in the male mouse the same receptor may have an important influence on control of vascular permeability. It may also be concluded that influences of the ERβ on distensibility and permeability are not functionally linked in the mouse mesenteric artery. All procedures were performed in accord with current National guidelines.