Inhibitory effect of O-alkylated analogues of oxytocin and vasopressin on human and rat myometrial activity.

Analogues of oxytocin and vasopressin modified through O-alkylation (methyl, ethyl and butyl) at position 2 of the peptide chain were synthesized and tested for effects on the rat uterus in vivo and on isolated rat and human myometrial preparations. None of the analogues showed any appreciable oxytocic activity. When tested together with oxytocin or vasopressin the analogues inhibited the uterine response to the hormones in a dose-dependent and reversible way. Ethyl-analogues were more powerful antagonists than methyl-analogues but further prolongation of the alkyl-chain (butyl) diminished the antagonistic properties of the compounds. The effect of antagonistic potency of deamination at position 1 of the analogues varied among the analogues and depended on the test system used. The possible clinical value of the antagonists is discussed.