Contraction of lactating rat mammary gland in response to direct mechanical stimulation

¹ Department of Physiology and Biophysics, University of Tennessee, Memphis, Tennessee

Experiments were performed to determine whether the mammary gland myoepithelium of the lactating rat responds to direct mechanical stimulation. Rat pups on postpartum day 14 obtained 8.6 and 12.2% of the total extractable milk in the mammary glands in 31–41 min from anesthetized spinal cord-sectioned and sham-operated mothers, respectively. The mammary glands of both groups responded with a rise in intramammary pressure following mechanical stimulation of the skin overlying the cannulated mammary gland. The responses occurred after a latent period of 1–2 sec, attained an amplitude of 1–13 cm H₂O, and lasted 8–18 sec. Summation of the responses did not occur. Temporary fatigue of the response could be induced with repetitive stimuli. Stimulation of mammary glands contralateral to or adjacent to the cannulated gland never produced a response in the cannulated gland. The exposed mammary gland responded to lightly applied mechanical stimulation with alveolar contractions confined to the area of stimulus contact. Each rat responded to intravenous oxytocin (25 mU) with a 10–29 cm H₂O intramammary pressure rise of 4–31 min duration.

Key Words: mammary gland myoepithelium • spinal cord section • lactating • lactation • intramammary gland • pressure • milk ejection • milk • rat • contraction of myoepithelium

Submitted on June 1, 1964

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