Actions of oxytocin and a long-acting carba oxytocin analog on the porcine myometrium in vitro and in vivo.

The contractile actions of oxytocin and its analog 1-desamino-1-monocarba-[2-Tyr(OMe)]-oxytocin were compared on in vitro (experiment 1) and in vivo (experiment 2) preparations of porcine uterine horns. In both experiments, sows in estrus were selected for maximal sensitivity. Despite the loss of peak amplitude associated with the substitution at sequence position 2 of O-methyltyrosine for tyrosine, the two remaining alterations (N-terminal desamination and replacement of the 1-6 S-S bridge by CH2S) prolonged the action of single-dose presentations. Thus, instead of having a response lasting minutes when the parent hormone is given, an IV dose of about 5 micrograms of the analog/kg of body weight in the intact anesthetized sow resulted in a response lasting two hours.