Relaxant and contractile effects of some amines and prostanoids in myometrial and vascular smooth muscle within the human uteroplacental unit.

Tissue specimens of human myometrium and placenta were obtained at caesarean section and normal vaginal deliveries. Strips of myometrial tissue, and segments of intramyometrial arteries, chorionic plate arteries and veins, and stem villous arteries were dissected. The preparations were mounted in organ baths, and isometric tension was recorded. In myometrial preparations, prostaglandin F2 alpha (PGF2 alpha), prostaglandin E2 (PGE2), noradrenaline (NA) and serotonin (5-HT) all caused concentration-related contractions. In vascular preparations, the maximum contractant or relaxant effect, Emax or Imax, and the drug concentrations causing half maximum responses, EC50 or IC50 were determined. In intramyometrial arteries no significant differences between Emax or EC50 values were found for NA, 5-HT and PGF2 alpha. The Imax values (relaxation of vessels contracted by vasopressin) ranged prostacyclin (PGI2) greater than PGF2 alpha = PGE2, and the IC50 values PGF2 alpha = PGE2 = PGI2 (PGF2 alpha less than PGI2). Thus, PGF2 alpha showed dual effects. Only PGI2 relaxed placental vessels contracted by PGF2 alpha. In chorionic arteries, Emax values ranged PGE2 = PGF2 alpha greater than 5-HT greater than NA, and IC50 values 5-HT less than NA = PGF2 alpha = PGE2. In stem villous arteries, Emax ranged PGE2 = PGF2 alpha greater than 5-HT = NA, and EC50 5-HT = NA = PGE2 = PGF2 alpha. In chorionic veins the order of Emax values was PGF2 alpha = PGE2 greater than 5-HT greater than NA, and that of the EC50 values 5-HT less than NA = PGF2 alpha = PGE2. Smooth muscle tissues from the human uteroplacental unit show individual responses to prostanoids and amines, probably reflecting individual mechanisms for control of contractile activity and blood flow.