STUDIES OF AUTACOID RESPONSIVENESS AND ENDOTHELIUM DEPENDENCY IN HUMAN UMBILICAL ARTERIES

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.