Constriction of Human Umbillcal Arteries

Experiments on perfused segments or isolated rings of human umbilical artery showed that the magnitude of their contraction in response to bradykinin, epinephrine, or serotonin depended on the Po 2 of the perfusing or bathing solution. Constriction to bradykinin varied directly with the O 2 tension and was greatest when the Po 2 was approximately that of umbilical arterial blood during the transition from the fetal to the neonatal period. Catecholamine beta-receptors were not demonstrated (not present or not functional) in the umbilical artery, since there was no vascular response to either isoproterenol or to propranolol. Alpha-receptors were not required for O 2 or bradykinin constriction since these agents constricted the umbilical artery after enough phentolamine had been given to block constriction by norepinephrine. Because of the interaction between O 2 and vasoconstrictor agents the O 2 environment of umbilical vessels must be rigidly controlled in experiments measuring vascular reactivity. Sensitization by O 2 to the effects of chemical substances endogenous to the fetus or mother may play an important role in circulatory adjustments essential for neonatal life.