ANATOMY AND DEVELOPMENT OF THE SINOATRIAL VALVES IN THE DOGFISH (SCYLIORHINUS-CANICULA)

Background: We describe the adult anatomy and the development of the c ardiac sinoatrial valves in the dogfish (Scyliorhinus canicula). Metho ds: We use scanning electron microscopy, histological and histochemica l techniques in 39 hearts from embryos and adult specimens. Results: T he sinoatrial valvular set of the adult dogfish is composed of two tra nsverse valves laterally attached to the sinoatrial junction at their bases, Both valves are composed of two muscular layers, the sinusal an d the atrial, whose histological features are similar to the cardiac w all which they face. Collagen bundles, elastic fibers and fibroblasts ape present between the muscular layers, The extracellular matrix betw een the valvular layers also contains sulphated and non-sulphated glyc osaminoglycans. The sinoatrial valves develop from two lateral infoldi ngs of the cardiac wall, The left fold is deeper than the right, causi ng a shift of the sinoatrial communication to the right, The epicardiu m progressively covers the outer sinoatrial groove and the space betwe en the folds becomes populated by mesenchymal cells, The posterior atr ioventricular endocardial cushion is in contact with the base of the l eft fold until the embryo has about 40 mm TL. Conclusions: The sinoatr ial valves, in the dogfish, develop from lateral infoldings of the car diac wall, This origin results in histological and histochemical diffe rences between the two muscular layers which constitute the valves of the adult, The comparison of the sinoatrial valve morphogenesis betwee n the dogfish and some higher vertebrates suggests that the right sino atrial valve, but not the left, is homologous throughout the vertebrat e phylogeny. (C) 1997 Wiley-Liss, Inc.