Hypoxia: a stimulus for tissue plasminogen activator release in humans?

Six healthy male volunteers between the ages of 22 and 33 years inspired normoxic (20.9% O2) and hypoxic (10% O2) gas mixtures continuously for 15 min on separate days while resting supine. The order of testing was counterbalanced. Heart rates (b.min-1), minute ventilation (L.min-1), transcutaneous PO2 (mm Hg) and euglobulin lysis times (min) were determined at the onset and at regular intervals. Heart rates and minute ventilation increased significantly with most of the change occurring by min 5. Transcutaneous PO2 declined exponentially but stabilized by min 10. Euglobulin lysis time response was highly variable with individual changes from 2-38% observed. Further, the group appeared to fall into two classes that could be described as responders versus non-responders. The variability of these data suggest that hypoxia may not be a direct cause of tissue plasminogen activator release into the circulation but that susceptible individuals may exhibit a substantial fibrinolytic response to hypoxia. Those factors that explain the variability require further elucidation.