Effect of oxytocin on myoepithelium of the breast

¹ Reproductive Physiology Laboratory, Department of Obstetrics and Gynecology, New York Medical College, Flower and Fifth Avenue Hospitals, New York City

A laboratory study was made of the response of the myoepithelium of the postpartum human breast to synthetic oxytocin, comparing the effects of intranasal and intravenous administration. A clinical study was also undertaken to assess the effects of intranasal oxytocin on breast engorgement. Intramammary pressure was obtained directly through a polyethylene catheter placed in the mammary duct and connected to a pressure transducer and Poly-Viso recorder. A myoepithelial response was elicited by a threshold dose of 2 mU of oxytocin intravenously. Intranasal spray produced responses similar in amplitude to intravenous doses when applied in amounts 200 times the intravenous dose. The response pattern of intranasal spray was that of a series of contractions, whereas intravenous doses produced single contractions. The lag time from administration to response was 100 sec with intranasal oxytocin vs. 20 sec with intravenous doses. Clinically, a twice-a-day application of intranasal spray oxytocin appeared to accelerate the normal physiologic process of involution in nonnursing mothers.