Abstract
Following conclusion is obtained from the results and the discussion.
Morphological studies on rat embryos and jounglings by electron microscopy clarified that the obliteration process of the ductus arteriosus begins at the intrauterine life and the process is complicated phenomenon which is composed of interruption of elastic layers between muscle layers, appearance of mucoid substance in the intimal cells, dis-arrangement of the cells, and degeneration and proliferation of smooth muscle cells in the ductus arteriosus. During this process, it is not ascertained that damage of vasa vasorum and nerve-reflex mechanism play principal roles.
Furthermore, from the study on the cell-kinetics employing H3-thymidine in the ductus arteriosus during the obliteration, the hypertrophy of intimal cells at the obliteration (marked cell proliferation in the intimal layers of the ductus) has not been confirmed.
From these evidences, it is reasonable to consider that the obliteration of ductus arteriosus is due rather to the migration of cells into the vascular lumen, and not to the proliferation of the intimal cells. This finding supports the result of previous paper by Mato and Aikawa.
