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

Laboratory of Cellular and Molecular Physiology, School of Medicine, Universidad Los Andes, Santiago, Chile 6782468

Submitted 20 October 2003 ; accepted in final form 22 December 2003

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 17-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 ₂-isoform (44%) compared with male-derived aortas. Furthermore, estradiol upregulated the expression of ₂ 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 ₂-isoform in females.

acetylcholine; sodium nitroprusside; ouabain; vascular relaxation; rat aorta

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