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

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Abstract
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 F2α(PGF2α), prostaglandin E2(PGE2), noradrenaline (NA) and serotonin (5‐HT) all caused concentration‐related contractions. In vascular preparations, the maximum contractant or relaxant effect,EmaxorImax, and the drug concentrations causing half maximum responses, EC50or ICS0were determined. In intramyometrial arteries no significant differences betweenEmaxor EC50values were found for NA, 5‐HT and PGF2α. TheImaxvalues (relaxation of vessels contracted by vasopressin) ranged prostacyclin (PGI2) > PGF2α= PGE2, and the IC50values PGF2α= PGE2= PGI2(PGF2α< PGI2). Thus, PGF2αshowed dual effects. Only PGI2relaxed placental vessels contracted by PGF2α. In chorionic arteries,Emaxvalues ranged PGE2= PGF2α> 5‐HT > NA, and IC50values 5‐HT < NA = PGF2α= PGE2. In stem villous arteries,Emaxranged PGE2= PGF2α> 5‐HT = NA, and EC505‐HT = NA = PGE2= PGF2α. In chorionic veins the order ofEmaxvalues was PGF2α= PGE2> 5‐HT > NA, and that of the EC50values 5‐HT < NA = PGF2α= 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.