Intrinsic responses of rat coronary arteries in vitro: influence of testosterone, calcium, and effective transmural pressure.

Administration of testosterone to men with angina has been shown to reduce myocardial ischemia. The mechanism of this effect is not clear but could be via an influence on coronary artery tone. We therefore employed an animal model to study the intrinsic responses of coronary arteries mounted in the wire myograph and evaluated the effect of testosterone on coronary artery tone in vitro. Intrinsic responses of the vessels and response to addition of testosterone were observed. Immediately after loading, vessels relaxed, an effect that was dependent on the baseline transmural pressure of vessels and was attenuated by pretreatment with N-nitro-L-arginine methyl ester. Subsequent contraction to a peak wall tension (intrinsic tone) was abolished by removal of extracellular calcium. Addition of testosterone produced a significant dose-dependent relaxation of intrinsic tone in all groups studied. The lowest concentration at which relaxation occurred was 10-6M. We conclude that rat coronary arteries exhibit calcium-dependent intrinsic responses and develop spontaneous tone. Furthermore, addition of testosterone reduces intrinsic coronary artery tone. These findings may have important implications for men with angina and low plasma testosterone levels.