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nant, an intravenous drip of synthetic oxytocin is a powerful elixir. The drug most commonly used to induce labor in the U.S., oxytocin is also a natural hormone made in the hypothalamus and released into the bloodstream by the posterior pituitary gland. During labor, oxytocin stimulates the uterine muscle to contract. A long-pregnant woman's uterus responds so strongly and readily to both the natural and synthetic versions because she has more oxytocin receptors at childbirth than at any other time in her life. By the time she gives birth, oxytocin receptors in her uterus have climbed to 300-fold their normal levels. Oxytocin was discovered in 1909 when Sir Henry H. Dale found that an extract from the human posterior pituitary gland contracted the uterus of a pregnant cat. (The hormone is found unchanged in every mammalian species.) Dale named the unknown substance oxytocin, using the Greek words for "quick" and "birth." As early as 1911, physicians began using the pituitary extract to stimulate childbirth contractions. Dale subsequently found that the same extract facilitates the release of mother's milk. Oxytocin contracts the smooth-muscle cells surrounding the mammary glands to move milk into the nipple—called milk "let-down." About 50 years later, the biochemist Vincent du Vigneaud took up the potent pituitary substance. Throughout his career, du
OXYTOCIN Name: Oxytocin CAS Registry: 50-56-6 Other names: Pitocin, Syntocinon, Uteracon Did you know that Swiss researchers have recently reported that doses of oxytocin significantly increased the level of trust that people placed in strangers who were handling their money?
Vigneaud studied how structure relates to function in biologically important compounds, and he set out to define oxytocin's structure. By 1953, he had identified the nine amino acids, set them in the right order and handedness, and discovered the biologically important disulfide bond between two cysteines that creates a ring in the peptide hormone. To be sure he had it 94
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nursing. For example, during orgasm, oxytocin levels sharply peak in both men and women. (Oxytocin may facilitate the transport of sperm, some researchers suggest.) right, du Vigneaud synthesized the com- Animal studies also show that simply after pleasant warmth or rhythmic touch, oxypound—the first synthesis of any peptide tocin levelsrise.Oxytocin injections in anhormone. His work resulted in a Nobel imals can, among other things, decrease Prize in Chemistryfordu Vigneaud in 1955. blood pressure, encourage urination, and Synthetic oxytocin, also called Pitocin speed wound healing. Release of oxytocin or Syntocinon, is now regularly prescribed 0 in the brain reduces anxto induce as well as augiety, increases the pain ment labor. The Journal of threshold, and reduces theAmerican MedicalAssodepression in animal ciation estimated in 1998 models. that 16% of labors are induced in the U.S., and an Oxytocin researcher additional 16% of labors Kerstin Uvnàs Moberg, that start spontaneously professor of physiology are augmented with inat the Swedish Univerducing drugs. Oxytocin is sity of Agricultural Scialso administered just afences, suggests t h a t ter birth to prevent postoxytocin is the leading partum hemorrhage if hormone in a physiologthe uterus does not conical system that calms tinue to contract and stop the body and promotes bleeding. Less common- LOVING Oxytocin helps social bonding. Moberg ly, a nasal spray of oxy- mothers and babies bond writes in her book "The tocin is sometimes given Oxytocin Factor" that to mothers who have trouble with milk oxytocin has the opposite effect of "fightlet-down in the first few days of nursing. or-flight" hormones vasopressin and adrenaline, which increase stress, danger-readiFor many years, researchers saw oxyness, and wariness of strangers. Oxytocin, tocin primarily as a pregnancy hormone she says, helps the body relax and encourbecause of its starring roles in childbirth ages romantic, family, and pair bonding. and nursing. Scientists are now, however, Her hypothesis is supported by studies revealing many subtle, lifetime effects of that show social bonds are made when oxyoxytocin in both men and women. Oxytocin levels are high. Female rats that retocin, it turns out, functions much more ceive an injection of oxytocin begin to disbroadly than scientists had realized. play maternal behavior toward nearby rat Researchers began to suspect a broadpups whether the females have had offer role for oxytocin when they saw that the spring or not and whether the pups are same receptor that reaches such high contheirs or not. If a female vole standing next centrations in the laboring uterus is found to a male vole receives an injection of oxyin other tissues in both men and women, tocin, she will later show a preference for including the brain, heart, and reproducthat male vole over others. In humans, oxytive tract. Some researchers suspect, in adtocin plasma levels were higher and blood dition, that there are one or more as-yetpressure was lower in premenopausal unidentified oxytocin receptors. Oxytocin plays a large, and largely un- women who said they got more hugs from a spouse or partner. explored, role in the brain. Oxytocin is not Such pleasant effects from one small only a hormone that circulates in the bloodpeptide has stimulated research into crestream, it is also a neurotransmitter that ating an oxytocin pill. An intravenous drip travels along nerve cells in the brain and for labor induction works fine—but for elsewhere. The cells that make oxytocin in other indications, patients prefer somethe hypothalamus and send it to the pituthing that can be swallowed. The stomach, itary gland also send oxytocin to different regions of the brain. Moreover, cells of the however, breaks down peptides. Even once in the blood, oxytocin is inactivated withhypothalamus are not the only cells that make oxytocin. The ovaries, testicles, heart, in minutes by the enzyme oxytocinase. Getting an oxytocin drug into the brain is and blood vessel walls have all been shown an even greater challenge. For the time beto produce their own oxytocin. ing, we'll have to make do with more freBlood and brain levels of oxytocin rise quent hugS.-LOUISA DALTON in instances outside of pregnancy and WWW.CEN-0NLINE.ORG
