Differences in development of coronary arteries and veins

The differentiation of the coronary vasculature was studied to establish in particular the formation of the coronary venous system. Antibody markers were used to demonstrate endothelial, smooth muscle, and fibroblastic cells in serial sections of embryonic quail hearts. The anti-beta myosin heavy chain and the neuronal marker HNK-1 were added to our incubation protocol. In HH32, the coronary vascular network has developed into a circulatory system with connections to the sinus venosus, the aorta and the right atrium. The connections between the aorta and the right atrium allow for direct arteriovenous shunting. Subsequently, differentiation into coronary arteries and veins occurs with an interposed capillary network. The smooth muscle cells of the coronary arterial media derive from the subepicardial layer, whereas the subepicardially located cardiac veins recrute atrial myocardium, as these cells express the beta-myosin heavy chain antigen. Ganglia are located in the subepicardium close to the vessels, while nerve fibres tend to colocalize with the formed vessel channels. A new finding is presented in which the subepicardial coronary veins have a media that consists of myocardial cells. The close positional relationship of neural tissue and coronary vessels that penetrate the heart wall is explained as inductive for vessel wall differentiation, but not for invasion into the heart.