Use of ultrasound for noninvasive study of blood vessel responsiveness.

To provide a noninvasive means for studying individual macroscopic blood vessels, an ultrasound scanner was modified to provide a recording of blood vessel diameter. The instrument has A- and B-modes of signal display. The B-mode is used to position the probe and the A-mode to measure vessel diameter. The A-mode has two electronic gates for tracking the echo from each of two structures, i.e., near and far wall of vessel. The front gate was modified to pick up the falling rather than rising edge of a peak generated by the vessel wall. An analog signal proportional to the distance between gates was derived for recording with a strip-chart recorder. Probe holders were constructed to optimize positioning and holding of probe. Stability was excellent (reading varied 0.05 mm over 1 h). Axial resolution was between 0.3 and 0.73 mm. Discrepancy of measurements of plastic tubing made by ocular and ultrasound varied from 1.1 to 4.6%. Discrepancy with lightly fixed vessels was 2.7-8.2%. Ex vivo measurements on vessels with viable smooth muscle were more variable, perhaps because of actual change during measurements. Changes in vessel diameter induced by change in hydrostatic pressure and exposure to histamine were recorded.

Expression of factor V on human umbilical vein endothelial cells is modulated by cell injury.

Since human endothelial cells synthesize Factor V but do not secrete it into the medium, we studied the effects of cell injury on the availability of Factor V at the surface of these cells. Human umbilical vein endothelial cells (HUVEC), grown to confluency and incubated with human 125I Factor Va, specifically bound 5000 to 7000 molecules per cell. In the absence of added Va, no antigen was detected on adherent HUVEC with either labeled anti-V(Va) monoclonal or polyclonal IgG. However, exogenous Va, not V, prebound to these cells allows binding of labeled 125I anti-V(Va). Immunodectectibility of bovine Factor V contributed by fetal calf serum in the concentration used in cultures is less than 0.1% of that detected in human plasma. HUVEC, suspended by scraping from dishes, specifically bound 4000 molecules/cell of 125/I monoclonal IgG against V(Va). Although undisturbed cells excluded trypan blue, dye uptake by many of the suspended HUVEC indicated cell injury. Quantitation of injury by 51Cr release after scraping followed by multiple passages through an 18 g needle showed that 51Cr release increased with number of manipulations up to 60% and was observed almost immediately after manipulation. We suggest that little Factor V(Va) is present on the surface of intact adherent HUVEC. However, mechanical injury to HUVEC released or exposed endogenous Factor V(Va), resulting in expression of V that might mediate Factor Xa binding as well as activation of protein C by thrombin. Thus, injured, but not intact, HUVEC could participate in both promoting and limiting blood coagulation.