A Transient Fall in Pressure Precedes the Characteristic Intramammary Pressure Rise Following Mechanical Stimulation of the Mammary Gland. ∗

Summary

Mechanical stimulation of the mammary glands of lactating rats, and in the one rabbit tested results in an initial reduction in intramammary pressure prior to a rise in pressure of longer duration. The reduction in pressure is particularly marked when mechanical stimulation is applied during an existing rise in intramammary pressure due to a previous oxytocin or mechanical stimulation. Summation of responses did not occur when either two consecutive mechanical stimuli or an oxytocin plus a mechanical stimulus were applied; in fact the normal intramammary pressure response to oxytocin was reduced following repeated mechanical stimulation. Neither denervation nor intraductal filling of the mammary gland with lignocaine affected the response pattern.