Fibrinolytic activity without fibrinogenolysis during long-distance racing in horses

Fourteen horses were studied during a 157-km endurance ride. Two humans who ran the 157 km were also evaluated at the finish. Fibrin monomer samples were examined by two-dimensional gel electrophoresis and sodium dodecyl sulfate polyacrylamide gel electrophoresis. Two major species of horse Beta-chain with higher molecular weights and different isoelectric mobilities than human beta-chain were observed. Horse alpha-chains had higher molecular weights than human alpha-chains but similar alpha-chain heterogeneities. Mean euglobulin lysis time (ELT) in the horses was accelerated to similar levels throughout the ride (52% of control at 44 km, P less than 0.01), but mean plasma clot lysis time (PCLT) decreased progressively during the ride (30% of control at finish, P less than 0.005). Similar values for ELTs and PCLTs were noted in the runners and horses at the finish. Although fibrinolytic activity was accelerated for an extended period by the strenuous activity of this long-distance race, no evidence of increased carboxyl terminal degradation of the A alpha-chain was observed. This study suggests that prolonged physiological stimulation of the fibrinolytic enzyme (plasmin) system is not responsible for fibrinogen A alpha-chain heterogeneities observed in horses and humans. It further demonstrates the usefulness of horses as models for the study of exercise-induced fibrinolysis.