The development of the coronary vessels and their differentiation into arteries and veins in the embryonic quail heart

Research concerning the em- bryologic development of the coronary plexus has enriched our understanding of anomalous coronary vessel patterning. However, the differen- tiation of the coronary vessel plexus into arteries, veins, and a capillary network is still incomplete. Immunohistochemical techniques have been used for whole mounts and serial sections of quail embryo hearts to demonstrate endothelium, vas- cular smooth muscle cells, and fibroblasts. From HH35 onward, the lumen of the coronary plexus was visualized by injecting India ink into the aorta. In HH17, branches from the sinus venosus plexus expand into the proepicardial organ to reach the dorsal side of the atrioventricular sul- cus. From HH25 onward, vessel formation pro- ceeds toward the ventral side and the apex of the heart. After lumenized connections of the coro- nary vessels with the aorta and right atrium are established, a media composed of smooth muscle cells and an adventitia composed of procollagen- producingfibroblasts are formed around the coro- nary arteries. In the early stage, bloodflow through the coronary plexus is possible, although connections with the aorta have yet to be estab- lished. After the coronary plexus and the aorta and right atrium are interconnected, coronary vessel differentiation proceeds by media and ad- ventitia formation around the proximal coronary arteries. At the same time, the remodeling of the vascular plexus is manifested by disappearance of arteriovenous anastomoses, leaving only capil- laries to connect the arterial and venous system. Dev. Dyn. 208:338-348, 1997. r 1997 Wiley-Liss, Inc.