Estradiol-induced expression of Na+-K+-ATPase catalytic isoforms in rat arteries: gender differences in activity mediated by nitric oxide donors

Abstract
We tested the hypothesis that previously demonstrated gender differences in ACh-induced vascular relaxation could involve diverse Na+-K+-ATPase functions. We determined Na+-K+-ATPase by measuring arterial ouabain-sensitive 86Rb uptake in response to ACh. We found a significant increase of Na+ pump activity only in aortic rings from female rats (control 206 ± 11 vs. 367 ± 29 nmol 86Rb/K·min–1·g wt tissue–1; P < 0.01). Ovariectomy eliminated sex differences in Na+-K+-ATPase function, and chronic in vivo hormone replacement with 17β-estradiol restored the ACh effect on Na+-K+-ATPase. Because ACh acts by enhancing production of NO, we examined whether the NO donor sodium nitroprusside (SNP) mimics the action of ACh on Na+-K+-ATPase activity. SNP increased ouabain-sensitive 86Rb uptake in denuded female arteries (control 123 ± 7 vs. 197 ± 12 nmol 86Rb/K·min–1·g wt tissue–1; P < 0.05). Methylene blue (an inhibitor of guanylate cyclase) and KT-5823 (a cGMP-dependent kinase inhibitor) blocked the stimulatory action of SNP. Exposure of female thoracic aorta to the Na+/K+ pump inhibitor ouabain significantly decreased SNP-induced and ACh-mediated relaxation of aortic rings. At the molecular level, Western blot analysis of arterial tissue revealed significant gender differences in the relative abundance of catalytic isoforms of Na+-K+-ATPase. Female-derived aortas exhibited a greater proportion of α2-isoform (44%) compared with male-derived aortas. Furthermore, estradiol upregulated the expression of α2 mRNA in male arterial explants. Our results demonstrate that enhancement of ACh-induced relaxation observed in female rats may be in part explained by 1 ) NO-dependent increased Na+-K+-ATPase activity in female vascular tissue and 2 ) greater abundance of Na+-K+-ATPase α2-isoform in females.