Abstract
1 The inhibitory effect of a commercial preparation of oxytocin (Syntocinon) was studied on the isolated vas deferens of the rat. 2 The inhibition of contractions to agonists and to field stimulation obtained were mimicked by appropriate dilutions of chlorbutol, a preservative present in Syntocinon. 3 Preservative-free synthetic oxytocin had no inhibitory effect on the tissue and slightly potentiated contractions evoked by field stimulation. 4 It is concluded that inhibitory effects of Syntocinon on the vas deferens are due to chlorbutol, not oxytocin.