Isometric pressure myography enables measurement of maximal vascular vasoconstriction and authentic EC 50

Both isometric wire and isobaric pressure myography have limitations. Wire myography distorts the vessel, may damage the endothelium, and limits intraluminal perfusion. On the other hand, occlusion of the vessel lumen may preclude measurement of maximal responses in the pressure myograph. We developed a system whereby the response of pressurized vessels could be measured under isometric conditions. We used the video dimension analyzer and servo controller of a classical pressure myograph (Living Systems Instrumentation) to maintain mesenteric and tail artery segments at a constant diameter by changing the intraluminal pressure. Concentration‐response curves for phenylephrine showed a classical sigmoidal form (pressure vs concentration), from which we were able to determine maximal response and EC 50 . The EC 50 for the mesenteric arteries was significantly lower by isometric pressure myography (4.5±0.7x10 −7 M, n=5) than by wire myography (Kent Scientific) (20.4±2.0x10 −6 M, n=7). On the isometric pressure myograph system, there was a rightward shift of the curve in the presence of prazosin. We propose that isometric pressure myography, which may be readily achieved with minimal modification of existing equipment, offers significant advantages over classical isobaric pressure myography. It allows for estimation of a true maximal constrictive response, and calculation of an authentic EC 50 . CIHR