Amplification of hormone receptors by neonatal oxytocin and vasopressin treatment.

: Newborn rats were treated once with 2 Units of vasopressin (VP) or oxytocin, respectively. At the age of 2 months and 1 year, respectively, the reactivity of isolated aortic strips to vasopressin and noradrenaline was tested. In young adults animals vasopressin pretreatment enhanced whilst oxytocin pretreatment decreased the responsiveness of aortic strips to VP. In elder specimens both types of pretreatment resulted in an increased late sensitivity to VP. The norepinephrine-sensitivity was higher in the young adults pretreated with oxytocin, whilst in the elder ones vasopressin-retreatment gave the same late effect. It could be established that the hormone excess produced in the neonatal age led to the "amplification" of hormone receptors and this alteration provided to be permanent. A compound which is similar to but not identical with the hormone--in our case, oxytocin--would elicit an alteration of a less unindirectional and permanent type; late sensitivity changes in both directions may occur.