Non-genomic activation of adenylyl cyclase and protein kinase G by 17β-estradiol in vascular smooth muscle of the rat superior mesenteric artery

The aim of the present study was to investigate the signaling mechanisms underlying the non-genomic effects of estrogen in rat superior mesenteric arteries. Isometric tension was recorded in rings with or without endothelium. Changes in cyclic nucleotide levels and protein kinase (PK) activities were measured. Localization of estrogen receptors (ER) and caveolin-1 were visualized by confocal microscopy. 17β-Estradiol elicited a concentration-dependent relaxation. The relaxation was reduced by SQ 22536 (adenylyl cyclase inhibitor) and KT 5823 (PKG inhibitor) while ODQ (guanylyl cyclase inhibitor) and KT 5720 (PKA inhibitor) had no effect. At the physiological concentration of 1 nM, 17β-estradiol had no significant effect on relaxation but enhanced the relaxation to sodium nitroprusside. The enhancement of relaxation by 17β-estradiol was blocked by SQ 22536 and KT 5823. Although 1 nM 17β-estradiol or 10 nM sodium nitroprusside given alone had minimal effects on PKG activity, in their combined presence, a significant increase in PKG activity was observed. Confocal microscopy demonstrated that ERα and ERβ colocalized with caveolin-1 and PKG in vascular smooth muscle cells. The present findings suggest that 17β-estradiol enhances relaxation of vascular smooth muscle of the rat superior mesenteric artery by activating adenylyl cyclase, leading to an increase in cAMP which cross activates PKG in the caveolae. No detectable increase in total cAMP level was detected as these changes occurred in the caveolae. These results are consistent with the notion that 17β-estradiol mediates its effect in the distinct microdomains of the caveolae of the plasma membrane with colocalization of adenylyl cyclase and PKG.