Abstract

The entry of ³H-norepinephrine and its accumulation and distribution through the depth of the isolated rabbit thoracic aorta wall was studied with an isotope frozen-section technique. If both surfaces of the vessel were exposed, tritium accumulated at the adventitio-medial junction and the inner layers of the media during the time course of contraction, to concentrations greater than could be accounted for by the extracellular space. If the intimal surface only was exposed, ³H concentration was highest near the intima and in the center of the artery. ³H entering through the adventitia rapidly filled part of the extracellular space of this tunica and collected in the junctional area. The balance of the adventitial extracellular space filled more slowly. ³H was distributed through the media in somewhat the same manner as that entering through the intima, but at a lower level and in the opposite direction. The junctional accumulation was in part cocaine-sensitive. The pattern of ³H entry through the media suggests a dense but generally homogeneous tissue; that through the adventitia, a tissue perforated by channels which allow rapid access and exit of material to and from the adventitio-medial junction, the site of the terminal sympathetic plexus.