PubMed · 38575
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H Wurm. 1979-06-30. [Vasoactive lipids (author's transl)].. https://pubmed.ncbi.nlm.nih.gov/38575/
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1. The human fetal extracorporeal circulation is normally a vasodilated, low pressure system. 2. As this vasculature lacks innervation, autacoids have been postulated as being of great importance in controlling its tone. 3. This has now been confirmed by pharmacological in vitro techniques, particularly utilizing perfusion of the isolated umbilical cord and placental lobule. 4. The fetal umbilical-placental vessels are sensitive to a wide range of vasoconstrictor autacoids, some of which can cause intense vasospasm. 5. Thromboxane A2 receptors have been identified in both umbilical vein and placental villous vessels. 6. Prostacyclin and endothelial cell-derived relaxing factor (or nitric oxide) may be largely responsible for the low vascular resistance normally found in the fetal extracorporeal circulation. 7. Immediately after birth it is likely that stimuli such as cooling, stretching and handling of the umbilical cord cause release of eicosanoids and other autacoids from the vessels, leading to their complete closure.
The effect of serotonin, prostaglandin E2 (PGE2) and PGF2 alpha on the smooth muscle tension in perfused human umbilical arteries was investigated before and after removal of the endothelium. Denudation was performed mechanically using a nylon filament loop, and the efficiency of the procedure was checked by electron microscopy. In non-denuded vessels the autacoids elicited biphasic pressure responses, all starting with a vasodilatation and followed by a strong vasoconstriction. After denudation no dilatatory responses were evoked, whereas the constrictory responses appeared to be unchanged. Pre-treatment of the vessels with methylene blue did not affect the autacoid responses. Generally the perfusion pressure decreased after the de-endothelialization, in some preparations to levels of about 50% of the initial perfusion pressure. In about one-third of the preparations exposure to methylene blue led to a definite pressure increase. The results indicate that endothelium-derived factors are involved in the autacoid responses and also in the maintenance of basic vascular tonus in the umbilical circulation.
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