Ultrastructural and immunohistochemical changes of the extracellular matrix during intimal cushion formation in the ductus arteriosus of the dog.

The changes of the intima during subendothelial edema formation were studied by ultrastructural and immunohistochemical methods in the ductus arteriosus (DA) of the dog. Subendothelial edema formation is the first stage in the development of intimal cushions in the DA. Development of intimal cushions is a physiological process preceding normal spontaneous closure after birth. The material consisted of normal canine DA and DA from a strain of dogs with hereditary persistence of the DA (PDA). In the normal DA intimal thickening starts with separation of the endothelial cells from the internal elastic lamina by a widened subendothelial region (SR). Initially this SR is, at the ultrastructural level, composed of granular and amorphous material. Collagen fibrils and elastin are not detected. During the formation of the SR a shedding of the basal lamina underneath the endothelial cells is observed. In the PDA the endothelial cells remain attached to the internal elastic lamina. The topography of the extracellular matrix components collagen type I, III, IV, fibronectin and laminin were studied immunohistochemically. These are important factors in the adherence of the endothelial cells to the underlying intimal layers. Laminin and collagen type I are diffusely present before but absent after detachment of the endothelial cells. Collagen type III, barely detectable before detachment, becomes visible underneath the detached cells. No changes are observed in the distribution of collagen type IV and fibronectin. Comparison of the normal DA with the various types of the PDA strain and controls allowed the conclusion that the observed changes in the extracellular matrix components were confined to those parts of the vessel wall that showed development of intimal thickening. The observed alterations both at the ultrastructural and immunohistochemical level do not explain the initiation of the process of endothelial cell detachment, which have been shown in a previous study to be related to an increase in hyaluronic acid.

Smooth muscle cell proliferation in the ductus arteriosus and the descending aorta, and effects of enalapril on SMC proliferation in perinatal rats.

This study was carried out to determine the proliferation profile of the smooth muscle cells (SMC) in the media of the ductus arteriosus (DA) and the descending aorta (Ao), and to examine the effects of the angiotensin-converting enzyme inhibitor enalapril on the proliferation of these cells in perinatal rats. The proliferating cell nuclear antigen (PCNA) index of the DA peaked in 19-day-old fetuses at 75%, and the index significantly declined in 20-day-old fetuses. The PCNA index of the Ao showed a similar profile until pups reached 1 day of age; however, the index of the Ao then increased in 3-day-old pups. The PCNA indices of the DA and Ao decreased significantly after maternal oral treatment with enalapril (10 mg/kg for 7 days), with a more marked decline in the DA than in the Ao. The PCNA indices of these vessels in 20-day-old fetuses were not altered by maternal treatment with enalapril. These results indicate that the SMC proliferation rate in the DA was similar to that in the Ao until pups reached the age of 1 day, and that the inhibitory effect of enalapril on the SMC proliferation was age-dependent and more prominent in the DA than in the Ao.