Observations on the sinuatrial nodal artery of the rat.

The structure of the sinuatrial nodal artery has been investigated in young and old rats. The nodal artery is derived from the internal thoracic artery, runs centrally though the node and supplies it by several branches. An extensive cuff of nodal cells is seen within the adventitia of the artery and its branches adjacent to the smooth muscle cells of the media. The cuff cells vary in both shape and myofibrillar content and contain acetylcholinesterase. The cuff is extensively innervated by both adrenergic and cholinergic axons. The significance of these findings with regard to earlier morphological and physiological reports is discussed.