Estimation of Amount of Oxytocin Released as Result of Nursing Stimuli in Lactating Rat.

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Abstract
The amount of oxytocin required for normal milk letdown in lactating rats was estimated. This was determined by injecting various doses of oxytocin intravenously into anesthetized mothers while young were actively sucking and comparing weight of milk obtained by young expressed as percent litter body weight with normal values. Nem-butal (3 mg/100 g) blocked milk let-down reflex and prevented removal of milk by the young. 0.5 USP/kg oxytocin restored normal milk withdrawal; .02 USPAg did not. Much greater yields were obtained with 01 USP/kg. Milk flow commenced with all doses after latent period of 5-10 seconds and lasted 4-5 minutes. It is concluded that normal 14-day postpartum lactating rats vary in amount of release of oxytocin following nursing stimuli from less than 0.02 to 0.1 USP/kg.