Morphine suppresses the oxytocin response
in breast-feeding women

Lindow SW, Hendricks MS, Nugent FA,
Dunne TT, van der Spuy ZM.
Department of Obstetrics and Gynaecology,
Medical School, University of Cape Town,
Observatory, South Africa.
Gynecol Obstet Invest 1999;48(1):33-7


The activity of opiate-mediated regulatory mechanisms of oxytocin secretion during breast-feeding was studied by the administration of either morphine, naloxone or placebo to women prior to the commencement of breast-feeding. Seventeen healthy women in the first week after delivery who had established lactation were randomized to receive either intravenous morphine 5 mg (n = 6), naloxone 2.4 mg (n = 6) or a placebo, sterile water (n = 5), which was given prior to commencement of breast-feeding. Oxytocin levels were measured by radioimmunoassay prior to initiation of breast-feeding and then at 2-min intervals until the feed was complete. Breast-feeding produced a significant rise in oxytocin levels in the control and naloxone groups but no significant rise in the patients given morphine. There was a significant reduction in oxytocin response following morphine administration when compared to placebo but not between naloxone and placebo. In conclusion, oxytocin secretion to breast-feeding is inhibited by exogenous morphine when compared to a control group but the administration of naloxone did not produce a significant difference from control.
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