The morphology and cell culture of the striated musculature of the rat azygos vein.

The azygos vein of the rat can be divided into three regions: The proximal cardiac region, where the wall is composed of two and sometimes three layers of cardiac muscle and a thin discontinuous layer of smooth muscle cells. Vascular casts of this region demonstrate layers of capillaries closely following the orientation of the cardiac fibres. A transitional zone, where both cardiac and smooth muscle cells interdigitate. In this zone, close associations between smooth muscle and cardiac muscle cells can be observed, however, gap junctions do not appear to be present. Beyond this transitional zone the vessel resembles a typical thin-walled vein. The cells of the media of the entire length of azygous vein have been isolated and grown in culture and two separate viable populations identified corresponding to smooth and cardiac muscle.