Prolonged action of deamino-carba analogues of oxytocin on the rat uterus in vivo

Deamino-oxytocin and some of its ‘carba’ analogues have a protracted effect on the rat uterus in vivo. Comparison of the elimination constants of the individual analogues of oxytocin and of deamino-oxytocin shows that the lower elimination rate of the analogues depends on the absence of the amino group in position 1 of the peptide chain. The individual modifications of the disulphide bridge influence the value of the elimination constants in different ways. Only the modification of hemicystine in position 6 of deamino-oxytocin resulted in an analogue with an even more prolonged action. The analogues with the most protracted action on the uterus, i.e. deamino-dicarba-oxytocin and deamino-6-carba-oxytocin, had a shorter antidiuretic action than oxytocin.