Endothelial-derived relaxing factor released by endothelial cells of human umbilical vessels and its impairment in pregnancy-induced hypertension. The principal objective of this study was to determine and compare the capability of human umbilical vessels of normal and pregnancy-induced hypertensive parturients to produce and to release the endothelial-derived relaxing factor. A bolus of bradykinin injected in the perfusion system of human umbilical vessels induces a release of a relaxant factor, detectable by bioassay, that is pharmacologically similar to the endothelial-derived relaxing factor. Human umbilical cords were collected from normal and pregnancy-induced hypertensive parturients. In the latter group the release of endothelial-derived relaxing factor is extremely reduced. In fact, in umbilical vessels collected from normal parturients, bradykinin at a dose of 20 pmol produces a release of endothelial-derived relaxing factor equivalent to a relaxation induced by 59.9 +/- 11.0 and 30.8 +/- 11.4 pmol of glyceryl trinitrate for the artery and vein, respectively. The same dose of bradykinin in umbilical vessels, collected from pregnancy-induced hypertensive parturients, produces a release equivalent to 6.6 +/- 2.2 and 5.7 +/- 3.5 pmol of glyceryl trinitrate equivalent for the artery and vein, respectively. Neither an increasing bolus of exogenous bradykinin or an infusion of superoxide dismutase or L-arginine was able to restore the production of endothelial-derived relaxing factor to normal levels. Our results indicate a probable alteration of endothelial cell numbers or an alteration of the enzymatic pathway, probably due to cytotoxic endogenous factors produced in pregnancy. 