EFFECTS OF NOREPINEPHRINE ON THE MECHANICAL-PROPERTIES OF THE HUMAN RADIAL ARTERY IN-VITRO

Background The human redial artery has been proposed as on alternative io coronary grafts in subjects with coronary ischemic disease. Becaus e this muscular artery is known to be prone to spasm, changes in its m echanical properties in response to catecholamines are important to in vestigate. Methods We describe a new echo-tracking technique of high r esolution that allows investigation, in vitro, of the diameter and the wall thickness of arterial cylindrical segments. In addition, a class ic tissue bath experiment is used to study the vasoreactivity of arter ial rings. Mechanical properties of the radial artery are determined o ver a 0 to 200 mm Hg range of transmural pressure in the presence and absence of norepinephrine in the perfusion medium. Results With tissue bath experiments, the norepinephrine dose-response curve was characte rized by on EC50 value of 1.48 +/- 1.09 10(-6) mol/L and a maximal dev eloped tension at 10(-5) mol/L. The results obtained with pressurized segments gave similar results with an EC50 value of 8.1 +/- 2.3 10(-7) mol/L and a maximal change in diameter at 10(-5) mol/L norepinephrine . Under the influence of 10(-5) mol/L norepinephrine, the radial arter y constriction reached 22%, significantly affecting the unstressed dia meter. Compliance did not show any significant change in the overall t ransmural pressure range, whereas distensibility significantly increas ed and elastic modulus significantly decreased. Conclusion The study s hows that the capacitive properties oi the human muscular radial arter y are maintained with norepinephrine not only through decreased stiffn ess of wall material but also through reduced unstressed diameter. Thu s drugs inducing smooth muscle relaxation may be helpful in preventing radial artery spasm after coronary grafts.