Vasoactive actions of local anaesthetics on human isolated umbilical veins and arteries

1. An in vitro study, using helical preparations of human umbilical arteries and veins obtained from healthy women at term pregnancy, was designed to determine: (a) whether three local anaesthetics commonly utilized in obstetric anaesthesia (bupivacaine, 2-chloroprocaine, and lignocaine) can induce contraction or relaxation of resting umbilical vessels; (b) whether these agents can induce contraction or relaxation of umbilical vessels which have been previously induced to contract by a known activator, potassium chloride (KCl); and (c) the relative potency of these agents as compared to KCl. 2. The results indicate that: (a) these local anaesthetics are vasoactive on human umbilical vascular smooth muscle; (b) bupivacaine induces contraction in over 90% of the resting vessels examined, while 2-chloroprocaine consistently causes relaxation and lignocaine causes a small degree of contraction in 40% of vessels examined; (c) bupivacaine causes further contraction (or potentiation) of KCl-contracted muscle in 50% of the vessels studied, while 2-chloroprocaine and lignocaine both induce relaxation of these contracted vessels.