LOCALIZATION OF TISSUE-PLASMINOGEN ACTIVATOR IN THE ENDOTHELIUM OF A LIMITED NUMBER OF VESSELS

The immunolocalization of tissue plasminogen activator (tPA) was asses sed in vessels of various sizes from baboons. Femoral artery and vein, carotid artery, aorta, and sections from basal ganglia and cerebral c ortex were stained for tPA and CD31, an endothelial cell-specific surf ace antigen. In each case, the endothelium of the large vessel stained positively for anti-CD31 but not for tPA. However, vascular structure s in the adventitia corresponding to the vasa vasorum were found to be associated with tPA antigen In situ hybridization of femoral artery w ith S-35-labeled cRNA probes defected tPA mRNA in the vasa vasorum but not the large vessel endothelium Analysis of the microvasculature of the basal ganglia and cerebral cortex showed limited immunohistochemic al staining for tPA; only 3% of the vessels measuring 4 to 100 mu were positive. Even so, tPA was mostly distributed within a narrow range o f vessel size; 90% of the positive vessels were classified as precapil lary arterioles and postcapillary venules (7.5 to 30.0 mu), whereas on ly 3% of the capillaries were positive, despite accounting for 40% of all vessels. Thus, tPA-containing endothelium are distributed mainly a ll smaller vessels, excluding the capillaries.