Estriol reduces the reactivity of the human umbilical artery to mechanical stimuli

The effect of estriol on the reactivity of the human umbilical artery to mechanical stimulation was studied using an in vitro perfusion method. The mechanical stimuli were produced by force applied to the outer surface of the vessel through a system consisting of a lever with equal length arms which was activated by small weights of known mass placed on one of the arms. The contractions of the preparations were proportional to the weights applied. When a 0.5-gram stimulus was applied, the mean contractile response of seven preparations was 46.7 +/- 2.72 mm Hg (mean +/- SEM). The addition of 10 micrograms/ml estriol to the nutrient fluid (Tyrode) caused a (mean 6.8 +/- 1.32 mm Hg) reduction of the response to the mechanical stimuli. We suggest that estrogens, and estriol in particular, play an important role in the modulation of the reactivity of the human umbilical artery during pregnancy in the presence of the mechanical stimulation caused by intrauterine fetal movements.