ABSTRACT
Testosterone has been added to hormone replacement therapy to treat sexual dysfunction in postmenopausal women. Whereas estrogen has been associated with vascular protection, the vascular effects of testosterone are contradictory and the effects of its association with estrogen are largely unknown. In this study we determined the effects of testosterone associated with conjugated equine estrogen (CEE) on vascular function using a model of hypertensive postmenopausal female: ovariectomized spontaneously hypertensive rats. Female spontaneously hypertensive rats were divided into sham-operated, ovariectomized (OVX), and OVX treated for 15 days with either CEE alone (OVX+CEE) or associated with testosterone (OVX+CEE+T). Angiotensin II (ANG II)-induced contraction was markedly increased in aortic rings from OVX compared with sham-operated rats. CEE treatment restored ANG-II responses, a beneficial effect abrogated with CEE+T. CEE treatment also increased endothelium-dependent relaxation, which was impaired in OVX rats. This effect was lost by CEE+T. Treatment of aortas with losartan (ANG-II type-1 receptor antagonist) or apocynin (NADPH-oxidase inhibitor) restored the endothelium-dependent relaxation in OVX and CEE+T, establishing an interplay between ANG-II and endothelial dysfunction in OVX and CEE+T. The benefits by CEE were associated with downregulation of NADPH-oxidase subunits mRNA expression and decreased reactive oxygen species generation. The association of testosterone with CEE impairs the benefits of estrogen on OVX-associated endothelial dysfunction and reactive oxygen species generation in rat aorta by a mechanism that involves phosphorylation of the cytosolic NADPH-oxidase subunit p47(phox).
Subject(s)
Aorta/drug effects , Endothelial Cells/drug effects , Endothelium, Vascular/drug effects , Estrogen Replacement Therapy , Estrogens, Conjugated (USP)/pharmacology , Hypertension/metabolism , Ovariectomy , Oxidative Stress/drug effects , Reactive Oxygen Species/metabolism , Testosterone/pharmacology , Angiotensin II Type 1 Receptor Blockers/pharmacology , Animals , Aorta/metabolism , Aorta/physiopathology , Disease Models, Animal , Dose-Response Relationship, Drug , Endothelial Cells/metabolism , Endothelium, Vascular/metabolism , Endothelium, Vascular/physiopathology , Enzyme Inhibitors/pharmacology , Female , Hypertension/genetics , Hypertension/physiopathology , NADPH Oxidases/antagonists & inhibitors , NADPH Oxidases/genetics , NADPH Oxidases/metabolism , Phosphorylation , RNA, Messenger/metabolism , Rats, Inbred SHR , Time Factors , Vasoconstriction/drug effects , Vasoconstrictor Agents/pharmacology , Vasodilation/drug effects , Vasodilator Agents/pharmacologyABSTRACT
OBJECTIVE: The increased risk of cardiovascular diseases in postmenopausal women has been linked to the decrease in plasma estrogen levels. Preparation of conjugate equine estrogens (CEE) is one of the most routinely used hormone therapy in postmenopausal women. However, studies on the vascular effects of CEE are still sparse and the mechanism of action is not completely elucidated. In this context, we have determined the effects of CEE in the vascular oxidative stress observed in ovariectomyzed (OVX) spontaneously hypertensive rats (SHR). Mechanisms by which CEE interferes with redox-sensitive pathways and endothelial function were also determined. RESULTS: Aortas from OVX rats exhibited increased generation of reactive oxygen species (ROS), NADPH oxidase activity and reduced catalase protein expression, compared to aortas from sham SHR. Endothelium-intact aortic rings from OVX were hyperreactive to NE when compared to Sham aortas. This hyperreactivity was corrected by superoxide dismutase (SOD), catalase, and endothelium removal. Treatment of OVX-SHR with CEE reduced vascular ROS generation, NADPH oxidase activity, enhanced SOD and catalase expression and also corrected the NE-hyperreactivity in aortic rings from OVX-SHR. CONCLUSION: Our study indicates a potential benefit of CEE therapy through a mechanism that involves reduction in oxidative stress, improving endothelial function in OVX hypertensive rats.
