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.