Fig. 1. Modeling of nitrous oxide (N2O) binding to tissue plasminogen activator (tPA). Nitrous oxide is predicted to bind within the primary specificity pocket S1, where the tPA inhibitor tPA Stop binds (A ). Dose-dependent inhibition by nitrous oxide of 25–75 vol% of the catalytic efficiency of humans (IC50= 32.14 ± 0.26 vol%) and murine (IC50= 35.12 ± 0.13 vol%) tPA. *P < 0.001 versus nitrous oxide of 25–75 vol% (B ). Dose-dependent inhibition by nitrous oxide of 25–75 vol% of tPA-induced brain thrombolysis in vitro in blood clots obtained from whole blood samples (IC50= 27.13 ± 1.04 vol%). **P < 0.01, *P < 0.05, #P < 0.1 versus controls treated with medical air (C ). Data are mean ± SEM. Control experiments were performed with medical air instead of nitrous oxide.