Gonadal hormones affect diameter of male rat cerebral arteries through endothelium-dependent mechanisms

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Abstract
Gender is known to influence the incidence and severity of cerebrovascular disease. In the present study, luminal diameter was measured in vitro in pressurized middle cerebral artery segments from male rats that were either untreated, orchiectomized (ORX), ORX with testosterone treatment (ORX+TEST), or ORX with estrogen treatment (ORX+EST). The maximal passive diameters (0 Ca2+ + 3 mM EDTA) of arteries from all four groups were similar. In endothelium-intact arteries, myogenic tone was significantly greater in arteries from untreated and ORX+TEST compared with arteries from either ORX or ORX+EST. During exposure toNG-nitro-l-arginine-methyl ester (l-NAME), an NO synthase (NOS) inhibitor, myogenic tone significantly increased in all groups. The effect of l-NAME was significantly greater in arteries from untreated and ORX+EST compared with arteries from ORX and ORX+TEST rats. Differences in myogenic tone between ORX and ORX+TEST persisted after inhibition of NOS. After endothelium removal or inhibition of the cyclooxygenase pathway combined with K+ channel blockers, myogenic tone differences between ORX and ORX+TEST were abolished. Wall thickness and forced dilation were not significantly different between arteries from ORX and ORX+TEST. Our data show that gonadal hormones affect myogenic tone in male rat cerebral arteries through NOS- and/or endothelium-dependent mechanisms.