Estrogen reduces mouse cerebral artery tone through endothelial NOS- and cyclooxygenase-dependent mechanisms.

Gender and estrogen status are known to influence the incidence and severity of cerebrovascular disease. The vasoprotective effects of estrogen are thought to include both nitric oxide-dependent and independent mechanisms. Therefore, using small, resistance-sized arteries pressurized in vitro, the present study determined the effect of gender and estrogen status on myogenic reactivity of mouse cerebral arteries. Luminal diameter was measured in middle cerebral artery segments from males and from females that were either untreated, ovariectomized (OVX), or OVX with estrogen replacement (OVX + EST). The maximal passive diameters of arteries from all four groups were similar. In response to increases in transmural pressure, diameters of arteries from males and OVX females were smaller compared with diameters of arteries from either untreated or OVX + EST females. In the presence of N(G)-nitro-L-arginine methyl ester, artery diameters decreased in all groups, but diameters remained significantly smaller in arteries from males and OVX females compared with untreated and OVX + EST females. After endothelium removal or when inhibition of nitric oxide synthase and cyclooxygenase were combined, differences in diameters of arteries from OVX and OVX + EST were abolished. These data suggest that chronic estrogen treatment modulates myogenic reactivity of mouse cerebral arteries through both endothelium-derived cyclooxygenase- and nitric oxide synthase-dependent mechanisms.