[Innervation of cardiac muscle tissue in rat pulmonary veins].

The pulmonary vein (PV) of 16 adult male Wistar rat was studied using synaptophysin immunohistochemistry and staining with toluidine blue and hematoxylin. Its intrapulmonary trunk wall was found to have a unique structure. The middle tunic contained cross-striated muscle tissue that was identical to the cardiac muscle tissue in posterior wall of the myocardial atrium. The thickness of the muscular tunic increased with the increase of vein diameter. The thickest layer of cardiac muscle fibers was located in the orifice of the main trunk, and the thinnest - in the lateral veins (50-100 microm in diameter), carrying the arterial blood from the respiratory portion of pulmonary lobe. Along their whole length, cardiac muscle fibers are densely innervated. Efferent synaptophysin-positive endings of the terminal plexus were found to be tightly associated with cardiac muscle fibers, capillaries of the media in the area of PV orifice and vasa vasorum of the adventitia.