Action Potentials in the Human Mammary Gland

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Abstract
In 14 tests with 3 nursing mothers, electrodes were applied to the right breast and connected with a string galvanometer. Records were taken before and during nursing at the left breast. In 8 of these experiments Pituitrin was injected either before or after nursing. The milk let-down sensation was signaled on the record by the subjects. In every test, the 1st stimulus whether it was nursing or injection, evoked the let-down sensation, but the 2d stimulus aid not. Yet, injection after the end of nursing induced a flow of milk from the right breast. In every experiment a slow negative galvanometer deflection occurred with the let-down, usually starting a few seconds before the sensation was signaled. In some experiments the 2d stimulus was followed by an electric response, even though no let-down was felt. The recorded action potentials, amounted usually to about 1 mv; their time relations were similar to those in the submaxillary gland, and were very much slower than those recorded from smooth muscle. Latencies and other time relations are given. The evidence supports the view that the let-down is a direct result of active secretion, and not of the release of preformed milk by smooth muscle. Use of Pituitrin injection is proposed for diagnosing the causes of failure of lactation, and for aid in establishing conditional reflexes in cases of interference caused by adverse nervous factors.

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