Evidence for Adrenergic and Cholinergic Components in Milk Let-Down Reflex in Lactating Rat.

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Abstract
The amount of milk obtained by litters of lactating rats treated with various ergot alkaloids, Dibenamine (N-(2-chloroethyl) dibenzylamine) or atroplne, was compared with control values previously obtained. All ergot drugs tested significantly blocked the let-down response. Methylergonovine (Methergine) was the most potent inhibitor, followed by the dihydro-ergotoxine complex (Hydergine) and dihydroergotamine (DHE 45) in that order. Results indicate action on central nervous system is probably responsible for some, or perhaps all, milk let-down inhibitory action of ergot drugs. This observation was based primarily on results with Methergine, a non-sympatholytic compound. Dibenamine evoked symptoms of central excitation which persisted for 30-45 minutes after injection though milk let-down was not inhibited in those animals who nursed during this period. Milk let-down, however, was significantly inhibited when the drug was injected 2 hours before nursing, after which time adrenergic blockade has occurred. Atropine induced a highly significant blockade of the let-down response when injected 150-220 minutes before nursing, but failed to block the response when administered 15-60 minutes before nursing. Oxytocin administered after any of these drugs restored normal milk let-down, indicating blockade was central rather than peripheral. It is postulated both adrenergic and cholinergic components are present in the neurohumoral arc responsible for discharge of oxytocin from the posterior pituitary gland.