Information Please: Oxytocin - The Hormone Of Love

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Last July, at La Leche League International's Physicians' Seminar in Anaheim, California, Dr. Niles Newton, Professor of Behavioral Sciences at Northwestern University in Chicago, spoke on "Oxytocin: Hormone of Orgasm, Birth, Breastfeeding, and Bonding." In the past, oxytocin has been ignored by researchers because its small molecular size made it difficult to study and because until recently scientists have given more attention to the hormones associated with fear, aggression, and stress. In the past few years, however, new studies have uncovered some amazing, previously unknown facts about oxytocin, which Dr. Newton calls "the hormone of love," and its effects on human behavior and family relationships.

Manufactured and released by the pituitary gland, oxytocin is crucial to labor, delivery, and successful breastfeeding. It acts upon the uterus and the milk-producing cells in the breast, but a significant amount remains in the central nervous system. A woman's oxytocin level is one factor that influences when labor begins. In fact, pitocin, a synthetic form of oxytocin, is sometimes used to stimulate labor artificially.

Dr. Newton believes that a mother's response to her baby is rooted in biology. The oxytocin released by breastfeeding is one reason a nursing mother is physically different from the mother who does not nurse her baby. But oxytocin does more than stimulate a mother's let-down or milk-ejection reflex (the tingling sensation sometimes felt by mothers when the milk-producing cells release milk into the milk ducts). Oxytocin also triggers nurturing behavior, which is "an essential ingredient in the success of reproduction," according to Dr. Newton. Animal studies confirm this. Since animals do not have a sense of duty or feelings of obligation toward their young, some physical mechanism must exist to trigger the maternal behavior necessary to ensure the survival of the young.

Dr. Newton reported on a study done at the University of North Carolina involving female rats who had never given birth. Oxytocin was injected into the brains of these rats and their behavior toward strange newborn rats was evaluated. The more oxytocin injected, the more maternal behaviors, such as nest building, were exhibited, and this effect was observed almost immediately after the oxytocin injection. In another study, when mother rats were injected with an anti-oxytocin hormone just after delivery, they showed no interest in their newborns.

In addition to helping bring mothers and babies closer, oxytocin may also strengthen the bond between men and women and help maintain family stability. Dr. Newton believes that oxytocin may be the "biological foundation upon which patterns of family life are built." Long considered to be a "female hormone," recent research has indicated that men have oxytocin levels as high as non-pregnant, non-lactating women, fueling Dr. Newton's speculation that oxytocin may trigger affectionate behavior and love in men as well as women. Both men and women release oxytocin with orgasm. Married couples, after lovemaking, and nursing mothers, after breastfeeding, all reported lower levels of anxiety and depression than a group of mothers surveyed after a bottle-feeding. Even eating triggers oxytocin release, which is another reason to share family mealtimes.

Current research also highlights oxytocin's role in breastfeeding. For example, one study indicates that the secretion of oxytocin is a conditioned response, meaning that a mother's body may produce oxytocin in response to familiar sights, sounds, or activities, not just from the direct stimulation of breastfeeding. In a small sample of nursing mothers, all showed an increase in oxytocin before the baby was put to breast. This will not surprise mothers who feel their milk let down when their babies cry. In fact, half of the women in the study experienced this. An increase in oxytocin levels was also measured in 30% of the mothers when their babies became restless and in 20% of the women as they were preparing to nurse. However, levels of prolactin -- the other hormone produced by nursing -- did not increase until the baby actually sucked at the breast.

In another study cited by Dr. Newton, mothers who were exclusively breastfeeding their infants had higher levels of oxytocin during feedings than mothers who were breastfeeding and giving formula supplements. Oxytocin levels during feedings rose from two to twenty-four weeks postpartum in the exclusively breastfeeding mothers, while the supplementing mothers experienced no rise.

There are many components working together to create a loving bond between mother and baby. Among these are eye contact, physical contact, and a pleasing smell. Breastfeeding contributes to all of these, intensifying feelings of motherliness and love.

REFERENCES

Johnston, J. M. and Amico, J. A prospective longitudinal study of the release of oxytocin and prolactin in response to infant sucking in long term lactation. J Clin Endocrinol 1986; 62:5.

McNeilly, A. S., Robinson I. C., Houston M. J., and Howie, P. W. Release of oxytocin and prolactin in response to suckling. Br Med J 1983; 286:257-59.

Newton, M. and Newton, N. The let-down reflex in human lactation. J Pediatr 1948; 33:693-704.

Newton, N. The role of the oxytocin reflexes in three interpersonal reproductive acts; coitus, birth and breastfeeding. In Clinical Psychoneuroendocrinology in Reproduction: Proceedings of the Serono Symposia 22, eds. L, Carenza, P. Pancheri, and L. Zichella. New York: Academic Press. 1978.

Pedersen, C. A., Ascher, J. A., Monroe Y., and Prange, A. J. Oxytocin induces maternal behavior in virgin female rats. Science 1982; 216:645-50.

Van Leengoed, E., Kerker, E., and Swanson, H. H. Inhibition of postpartum maternal behavior in the rat by injecting oxytocin antagonist into the cerebral ventricles. J Endocrinol 1986; 112:275-82.

Note: Would you like your doctor to know more about breastfeeding? Then invite him or her to attend La Leche League International's 18th Annual Physicians Seminar on July 11-13 in Boston. This year's theme is: "Breastfeeding: Awareness to Action." Send for a copy of the registration materials and deliver them in person!

La Leche League International, Inc.

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By Randee Romano

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