Prenatal development of coronary arteries in the rat: morphologic patterns

The aim of this work was to address spatiotemporal and morphologic patterns of coronary artery development in rats, based on immunohistochemical and ultrastructural studies of hearts at different stages of prenatal development. Griffonia simplicifolia I lectin and alpha-smooth muscle antibody were used to demonstrate endothelial cells and/or their precursors and smooth muscle cells, respectively. Ultrastructural examination was performed on ED14-16 hearts to study the morphology of the developing coronary arteries in different regions of the truncus arteriosus and adjacent myocardium. On ED14 endothelial-like cells present within the mesenchyme surrounding the outflow tract penetrated the aortic wall and the truncoconal proximal myocardium. On ED15 these penetrating cells formed vascular clusters, which were the first signs of presumptive vascular channels. Development of the coronary artery proceeded by coalescence of discontinous vascular clusters, formation of the lumen (vascular channels) and establishing a connection of the proximal part with the aorta. The second layer of cells around vascular channels (embryonic media) consisted of mesenchymal cells that were attracted to the immature vessel and were first seen on ED15. At this time no lumenized connection of the coronary artery with the aorta has been seen. After the lumenized connection of the coronary artery with the aorta had been established perivascular cells of the media started to differentiate into vascular smooth muscle, as was shown by alpha-smooth muscle actin-staining. Further development and differentiation of the media and adventitia proceeded distally (towards the apex).