Permeability of the post-ischemic rat aorta

The time course of the vascular permeability disorder following upon acute hypoxia and the fate of plasma substances entering the vessel wall in consequence of increased permeability were studied on the rat abdominal aorta rendered hypoxic for one hour by double ligature and recirculated for periods ranging from one hour to 30 days. The distribution and quantity of mural plasma inhibition were determined histochemically by means of a colloidal iron tracer and Prussian blue reaction and by photometric analysis, respectively. Plasma imbibition reached its maximum after recirculation for 24 to 48 hours and fell to an almost normal level after 10 days. Administration of the colloidal iron tracer on the second day of recirculation, when the permeability disorder was at its peak, showed plasma imbibition in every layer of the vessel wall. At seven days it was restricted to the outer third of the media and the adventitia. The endothelium is acting as the main barrier to mural plasma imbibition and in the case of a permeability disorder only the elastic lamellae constitute a temporary mechanical obstacle to the ingression of plasma.