Constriction of human umbilical artery induced by local anesthetics

In order to study the direct effects of local anesthetics on the umbilical artery, an in vitro perfusion technique, utilizing 3-cm segments of human umbilical artery obtained within 15 min of delivery, has been developed. Basal perfusion pressure (tonus) and the frequency of phasic contractions were determined in 37 arterial segments perfused for 240-min periods with Tyrode's solution containing lidocaine in concentrations of 2.0, 8.0 or 16 microgram/ml of bupivacaine in concentrations of 0.25 or 9.8 microgram/ml. A control group consisting of 11 arterial segments was perfused only with Tyrode's solution. The lowest concentration of each anesthetic approximated that reportedly present in the umbilical arteries following administration of epidural anesthesia during labor. Both lidocaine and bupivacaine induced dose-related increases of up to 100% in tonus above the control levels of approximately 60 mm Hg, statistically significant (p less than 0.05) except for 2 microgram/ml lidocaine. At the same molar concentration, bupivacaine was more effective than lidocaine (p less than 0.05). Both anesthetics also increased the frequency of phasic contractions. These data suggest that these agents may exert their effects on the fetus, at least in part, through a direct constricting action on the umbilical artery.