Formation of the coronary vasculature: a brief review.

Myocardial vascularization is initiated after endothelial cell precursors from the region of the liver or septum transversarium migrate to the newly formed epicardium. Blood island-like structures appear and form vascular channels along the epicardium and into the myocardium. Prior to this time myocardial cells receive nutrition directly from the ventricular lumen, a process which is facilitated by the highly trabecular arrangement of the ventricles. A venous system is formed prior to any evidence of arteries or arterioles. The formation of a vascular plexus in the region of the outflow tract is followed by penetration of these microvessels into the wall of the aorta. These ingrowing vessels merge, acquire a muscular coat and form the left and then the right coronary vessels. These events occur during a short period of time, e.g., 2 weeks in humans, 4 days in rats. Maturation of the arterial tree occurs primarily after birth. Our knowledge of the regulation of coronary vascularization during development is very limited. Accordingly, future studies need to focus on the role of growth factors, chemotactic factors, extracellular matrix molecules, and mechanical events.