IN NORMAL DEVELOPMENT PULMONARY VEINS ARE CONNECTED TO THE SINUS VENOSUS SEGMENT IN THE LEFT ATRIUM

Background: Classic theories describe that the common pulmonary vein d evelops as an outgrowth from either the sinus venosus or atrial segmen t. Recent studies show that the pulmonary veins are connected to the s inu-atrial region before its differentiation into a sinus venosus and atrial segment. Methods: The development of the sinu-atrial region wit h regard to the developing common pulmonary vein and the growth of the atrial septum was investigated in avian embryos, using both scanning electron microscopy and immunohistochemistry. Embryos ranging between stage HH12 and HH28 were incubated with QH-1 that recognizes quail end othelial cells and precursors, HNK-1, that appears in this study to de tect the myocardium of the sinus venosus, or with HHF-35, being specif ic for muscle actins. Also vascular casts of the heart were produced b y injecting prepolymerized Mercer into the vascular system. Results: I n preseptation stages the common pulmonary vein drains into the left p art of the sinus venosus, that is clearly demarcated by the sinu-atria l fold and HNK-1 expression. During atrial septation the left part of the sinus venosus, in contrast to the right part, loses its HNK-1 anti gen from stage HH23 onwards, while at the same time the sinu-atrial fo ld in the left atrial dorsal wall flattens and disappears. From stage HH25 onwards HNK-1 expression is restricted to the right part of the s inus venosus, which contributes to the right atrium. The myocardial at rial septum never expresses the HNK-1 antigen, suggesting that the sep tum is of atrial origin. Discussion: It appeared that the sinus venosu s does not only contribute to the sinus venarum of the right atrium, b ut also to the left atrium. (C) 1995 Wiley-Liss, Inc.