The actions of angiotensin II (A II), bradykinin, and 5-hydroxytryptamine (5-HT) were compared in vitro in vascular segments obtained from three regions of the human umbilicoplacental vascular tree at term. The three regions selected were the umbilical cord arteries, the chorionic-plate arteries, and the villous stem arterioles supplying the individual chorionic villi. Helically cut strips from the vessel segments from each region were suspended together in a physiologic slat solution (pH 7.4) and gassed with 95% O2: 5% Co2 at 37°C. Well defined contractile responses to bradykinin and 5-hydroxytryptamine were observed in all arterial strips. Angiotensin II, on the other hand, had little or not effect on umbilical arteries, a sluggish although real contractile effect on chorionic plate arteries, and a well-defined contractile response in the arterioles (25 to 100μ inside diameter) supplying chorionic villi. Dose-response data indicate that 5-HT is the most potent of the agents studied followed by BK and A II in both the umbilical and chorionic plate arteries. In the arterioles supplying the villous, however, A II is the most potent followed in turn by BK and then 5-HT. Comparison of the relative peak responses for each drug between the three regions studied indicates a rising sensitivity to A II from the larger arteries of the cord and chorionic plate to the arterioles supplying the individual villi. These findings suggest a marked sensitivity to angiotensin II of the resistance vessels of the human placental vasculature and further tend to support the theory that circulating fetal angiotensin II may contribute to the maintenance of placental vascular tone in humans.
