Diagnostic ultrasound activates pure prekallikrein.

Diagnostic ultrasound activates the contact phase of human coagulation. This has been seen in human blood or plasma or with purified factor 12. The present work aimed to quantify a possibly triggering action of ultrasound on purified prekallikrein, the second of the two main triggers of the intrinsic hemostasis cascade. Either 2.7 μg/ml human prekallikrein or for control 1 μg/ml kallikrein in 26% glycerol - 0.54% NaCl-10.6 mmol/l Na3 citrate pH 7.4, in emptied polypropylene coagulation monovettes (Sarstedt) were exposed to diagnostic ultrasound (Siemens Acouson Antares, 5 MHz, 0.6 TIB, 0.6 TIS) for 0-5 min at room temperature (RT). Fifty microliter samples were withdrawn in duplicate and placed into an U-wells high quality microtiter plate (Brand 781600). Then 10 μl 2 mmol/l chromogenic substrate HD-CHG-Ala-Arg-pNA in 0.45% NaCl were added, and the increase in absorbance with time (ΔA405 nm /t at 37°C) was determined by a microtiterplate photometer with a 1 mA resolution (PHOmo; anthos). Exposure to diagnostic ultrasound biphasically increased the chromogenic activity of a prekallikrein solution in 26% glycerol. About 3-4 min ultrasound at 23 °C generated about 0.02 μg/ml kallikrein, that means that about 1% of pure prekallikrein in glycerol was converted into kallikrein. Thus, diagnostic ultrasound activates purified human prekallikrein to kallikrein. The ultrasound energy seems to fold the latent proenzyme prekallikrein into the active enzyme kallikrein. This contributes to explain the triggering action of ultrasound on the contact system of plasmatic human coagulation. Conversion of only 1% of prekallikrein into kallikrein is absolutely sufficient to start the intrinsic coagulation cascade. The clinical consequence of this action of ultrasound on intrinsic coagulation is that patients at risk for thrombosis, for example, patients with insufficiencies of hepatocytes, AT-3, C1-ina, or fibrinolysis should be protected by low-molecular-weight-heparin prior to the exposure of ultrasound, especially upon its prolonged exposure.