HETEROGENEITY OF SMOOTH-MUSCLE CELLS IN EMBRYONIC HUMAN AORTA

Cellular composition of aortas from 5- to 12-week and 18- to 28-week-o ld human embryos were investigated using immunocytochemistry, scanning and transmission electron microscopy, The aorta of the 5- to 12-week- old embryos consisted of three sublayers differing in cellular composi tion, The inner sublayer adjacent to the endothelium contained round a nd ovoid cells with synthetic phenotype, In the intermediate sublayer, spindle-like cells ultrastructurally similar to smooth muscle cells w ere found, Cells of the outer sublayer resembled fibroblasts or poorly differentiated mesenchymal cells, There were not definite morphologic al borders between sublayers. In the 18- to 28-week-old embryo aorta t he intima was separated from media by internal elastic lamina, Intimal and innermost medial cells had predominately stellate shape and synth etic phenotype, The outer part of media contained spindle-like cells t hat had well developed contractile structures, Both the 5- to 12-week- old and the 18- to 28-week-old embryo aortic cells were positively sta ined for alpha-actin and myosin and negatively stained for macrophage antigens, Thus, the majority of embryo aortic cells appeared smooth mu scle cells, however there was a regional difference in shape and synth etic state of these cells.