[Occlusion of the ductus arteriosus in the rabbit. A light and electron microscopic study]

The development of changes appearing with the closure of ductus arteriosus was followed in mature rabbit foetuses with the help of light and electron microscopy. In the foetuses, in which there was no spontaneous respiration of atmospheric air before fixation the ductus remained opened. In smooth muscle cells of the media there were enlarged cisternae of the endoplasmic reticulum being partially decayed. The foetuses that respired for about one minute had the ductus contracted to various degree and the endothelial cells were expelled into the lumen. In the foetuses respiring for 10 minutes the ductus were more contracted. The endothelium was considerably waved and the agglomeration of smooth muscle cells appeared. In the endothelial and musclar cells the endoplasmic reticulum was richer, and in a lot of places considerably disturbed. The ductus of foetuses respiring for 15 minutes had the lumen completely closed. The smooth muscle cells had a significantly changed their internal structure. The possibility of the direct transformation of the endoplasmic reticulum of the smooth muscular cells into inclusion bodies during the ductus arteriosus closure is discussed.