Testosterone Modulation of Myogenic Tone in Rat Isolated Mesenteric Resistance Microvessels
Myogenic tone is the reflexive constriction of a blood vessel when the intraluminal pressure increases and is an important control mechanism in the mesenteric microvasculature. A previous study demonstrated that testosterone modulates myogenic tone in response to changes in intravascular pressures, albeit in larger vessels. However, information concerning testosterone's effect on myogenic tone in micro vessels is lacking. This study aimed to determine the modulation effects of testosterone on myogenic tone in the mesenteric resistance microvessels. Tertiary branches of the mesenteric artery were isolated from male Sprague Dawley rats and pressurized in an arteriograph chamber (Living Systems Instrumentation, St. Albans, Vermont). Mesenteric resistance arteries exhibited a decrease in diameter at 60, 75, 90, and 105 mmHg when placed in HEPES buffered physiological solution with calcium (1.8 mM). The vessels exhibited a significantly larger diameter at the same pressures when placed in HEPES calcium-free solution and EGTA (2 mM) demonstrating the calcium dependence of myogenic tone development in these vessels. In another series of experiments, the mesenteric resistance arteries were pressurized to a stationary pressure of 75 mmHg at which they developed myogenic tone. The vessels with tone were then exposed to different concentrations of testosterone ( 1 nM, 10 nM, and 1 [!M) and the vessel's diameter was measured and recorded at five minute increments. The vessels exhibited an increase in diameter at a nanomolar concentration of testosterone suggesting that testosterone has a vasodilation effect on myogenic tone in the mesenteric microvessels at physiological concentrations. To our knowledge, this is the first in vitro study to demonstrate a vasodilation of myogenic tone in response to testosterone in a systemic microvessel.