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1 Department of Physiology and Biophysics, Wright State University School of Medicine, Dayton, Ohio 45435-0927; 2 Department of Pharmacology and Toxicology, Medical College of Georgia, Augusta, Georgia 30912-2300; 3 Michael E. DeBakey Institute for Comparative Cardiovascular Science and Department of Veterinary Physiology and Pharmacology, Texas A & M University College of Veterinary Medicine, College Station, Texas 77843-4466; and 4 Department of Physiology, Northeastern Ohio Universities College of Medicine, Rootstown, Ohio 44272
Cardiovascular diseases are often considered to be a predominantly male health problem, and it has been suggested that testosterone exerts deleterious effects on cardiovascular function; however, few experimental studies support this suggestion. Moreover, the cellular and molecular mechanism(s) underlying vascular responses to testosterone is unknown. The present study has investigated the acute effects of testosterone on porcine coronary artery smooth muscle at the tissue and cellular levels. Contractile studies demonstrated that testosterone or dihydrotestosterone (a nonaromatizable metabolite) relaxed these arteries by an endothelium-independent mechanism involving potassium efflux. Direct evidence from patch-clamp studies confirmed that testosterone opened K+ channels in single coronary myocytes, and further analysis identified this protein as the large-conductance, calcium- and voltage-activated potassium (BKCa) channel. Moreover, inhibiting BKCa channel activity significantly attenuated testosterone-induced coronary relaxation. These findings indicate that testosterone relaxes porcine coronary arteries predominantly by opening BKCa channels in coronary myocytes, and this response may be associated with accumulation of cGMP. This novel mechanism may provide a better understanding of testosterone-induced vasorelaxation reported in recent experimental and early clinical studies.
steroid; vascular; ion channel; vasodilation; androgen
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