Oxytocin Oxytocin

Structural Formula Ball-arid-Stick Model Space-filling Model

^ = Carbon = Hydrogen = Oxygen ^ = Nitrogen = Sulfur

Year of discovery: 1952; Year of introduction: 1950s; Drug category: Neuropeptide hormone; Main uses: Induction of labor; Other brand names: Pitocin; Related drugs: Dinoprostone (Cervidil, Prostin E2), Misoprostol (Cytotec).

Oxytocin is a natural peptide hormone that stimulates uterine contraction and induces labor. It is intravenously administered to facilitate the progression of labor or to reduce bleeding after expulsion of the placenta. The infusion of oxytocin is adjusted to control the intensity and frequency of uterine contraction.1

Oxytocin is produced mainly in the hypothalamus and stored in the pituitary gland, but it is also synthesized in the ovaries, endometrium and placenta. The powerful contractile action of pituitary extracts on uterine smooth muscle first was recognized in the early 1900s. Oxytocin was isolated in 1928 at Parke Davis and Company along with a structurally closely related peptide hormone, vasopressin, which is a pressor and antidiuretic. The structures of these hormones were determined by Vincent du Vigneaud at Cornell University in 1953. He showed that each consists of nine amino acids and that they differ only in the amino acids in position 3 and 8. Six of the amino acid units are contained in a disulfide ring, du Vigneaud was awarded the Nobel Prize in Chemistry in 1955 for this work.

During childbirth, oxytocin secretion is stimulated by dilation of the cervix and vagina. During the last stage of pregnancy, uterine responsiveness to oxytocin is elevated because of increased expression of oxytocin receptors, which is stimulated by estrogen. Oxytocin also increases local prostaglandin production, which further stimulates uterine contraction. Oxytocin acts by binding to specific G protein-coupled receptors which initiate the physiological process leading to uterine contraction. Oxytocin is also implicated in milk ejection during breastfeeding.

In addition to these effects, oxytocin plays a role in social behavior. Animal studies have revealed that it enhances maternal behavior and reduces stress.2

The induction of labor can also be stimulated by prostaglandins, natural substances synthesized from fatty acids, that are involved in many physiological processes (see page 40). In addition to causing uterine contraction, prostaglandins assist in ripening of the cervix. Currently, only PGE2 (dinoprostone) is approved for the induction of labor (Cervidil, Forest Laboratories; Prostin E2, Pfizer), but PGF2ct (dinoprost), another natural prostaglandin used earlier, is also effective. Dinoprostone is administered locally. Misoprostol, an orally active synthetic PGE, derivative (see page 92), is also efficacious for induction of labor, but it is used in the US mainly for the prevention of NSAID-induced gastric ulcer.

Dinoprost Dinoprostone (Prostin E2™)

1. Reproduction 2006, 131. 989-998; 2. Nat. Neurosci. 2004. 7, 1048-1054; Refs. p. 105

Dinoprost Dinoprostone (Prostin E2™)

1. Reproduction 2006, 131. 989-998; 2. Nat. Neurosci. 2004. 7, 1048-1054; Refs. p. 105

Structural Formula

Structural Formula

= Hydrogen

Pregnancy And Childbirth

Pregnancy And Childbirth

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