STUDIES ON THE HORMONAL CONTROL OF THE MILK-EJECTION ACTIVITY IN LACTATING RABBITS

A study was made of the effect of synthetic oxytocin (Syntocinon Sandoz) and synthetic lysine-vasopressin (Vasopressin Sandoz) on the milk-ejecting activity of the lactating mammary gland of the rabbit. Both drugs were given by intravenous infusion except in some cases where oxytocin was injected intravenously in single doses.

Depending on the sensitivity of the mammary gland and the amount of oxytocin administered, infusion of this hormone gave a prolonged tonic increase in the milk pressure or a rhythmic series of pressure increases. Both these reactions could be counteracted appreciably by giving vasopressin simultaneously in doses of the order of 1:4 to 1:1 in relation to the dose of oxytocin. After withdrawal of vasopressin the original effect of the oxytocin in the milk-gland pressure was slowly resumed. Doses of vasopressin with ratios of 1:1000 – 1:5 or saline had little or no effect at all.

Intravenous administration of adrenaline also caused transient suppression of the effect of the oxytocin infusion. There was no evidence to indicate that vasopressin potentiated this effect.

These findings are discussed in relation to the clinical findings of disturbance in the milk let-down during different stress situations. Both vasopressin and adrenaline might be released during stress.