Subcellular effects of experimental oligohydramnios on the developing rat limb.

In the rat, the development of the limb bud can be impaired by amniotic puncture. Selective haemorrhages are observed within 1 hour of the treatment. An ultrastructural analysis was undertaken to uncover the cytological changes associated with these haemorrhages. The earliest effect of oligohydramnios is the appearance of a periendothelial oedema which separates the mesodermal cellular processes from the endothelial basal lamina. The loosening of the latter and the distortion of the endothelial cells occur almost simultaneously. Subsequent damage of the mesodermal cells ensues, the ectoderm and the preskeletal condensations remaining unaffected. Only general damage of the embryo affecting all tissues will lead to the complete necrosis of the limb bud and even to foetal death. The great variability of skeletal defects observed in amniocentesis syndrome can be accounted for by the higher resistance of the differentiating cells to a decrease in blood supply.