Smooth muscle effects of lidocaine, prilocaine, bupivacaine and etiodocaine on the human umbilical artery.

The smooth muscle effects on human umbilical arteries of four different local anaesthetic agents - lidocaine, etidocaine, prilocaine and bupivacaine - were studied. Lidocaine and etidocaine relaxed the arteries, etidocaine more profoundly than lidocaine. Prilocaine in the concentration range 10-1,000 micrograms/ml caused pronounced contractions. Bupivacaine consistently evoked a contractile response in the concentration range 5-25 micrograms/ml, but at lower and higher concentrations the response to this drug was inconsistent. The concentrations of lidocaine were determined in six human umbilical arteries following maternal epidural block with this agent and were found to be 0.1 - 1.7 micrograms/g tissue. The contractile actions of prilocaine and bupivacaine on the human umbilical arteries are undesirable and might be hazardous if high concentrations are attained, e.g. during paracervical block.