Oxytocin lactation

Oxytocin, a nonapeptide hormone secreted by the pituitary gland, functions by stimulating uterine contraction and lactation during childbirth. Its sequence was determined from the following evidence ... 

Oxytocin is required for lactation. Milk is initially secreted into small sacs (alveoli) within the mammary gland. These alveoli are surrounded by smooth muscle, which contract to eject the milk. The oxytocin receptor is the key receptor that mediates this ejection of the milk. 

The posterior pituitary is innervated by direct nervous stimulation from the hypothalamus, resulting in the release of specific hormones. The hypothalamus synthesizes two hormones, oxytocin and vasopressin. These hormones are stored in and released from the posterior pituitary lobe. Oxytocin exerts two actions (1) it promotes uterine contractions during labor, and (2) it contracts the smooth muscles in the breast to stimulate the release of milk from the mammary gland during lactation. Vasopressin is an antidiuretic hormone (ADH) essential for proper fluid and electrolyte balance in the body. Specifically, vasopressin increases the permeability of the distal convoluted tubules and collecting ducts of the nephrons to water. This causes the kidney to excrete less water in the urine. Consequently, the urine becomes more concentrated as water is conserved. 

Secretion of pituitary hormones is responsive to behavior and effects of experience. Consider, for example, the phenomenon of lactation, in which the sucking stimulus to the nipple triggers the release of oxytocin,... 

Because oxytocin is a uniquely mammalian hormone with a critical role in both birth and lactation, it was an obvious candidate for involvement in maternal behavior. In fact oxytocin has been termed the hormone of mother love (Klopfer, 1971 Newton, 1973). As mentioned above, animal research offers support for this hypothesis (Pedersen, 1996). However, evidence implicating oxytocin in human behavior only recently has begun to accumulate, and direct evidence for a behavioral effect of oxytocin in humans remains to be demonstrated. 

By comparing time-resolved and steady-state fluorescence parameters, Ross et alm> have shown that in oxytocin, a lactation and uterine contraction hormone in mammals, the internal disulfide bridge quenches the fluorescence of the single tyrosine by a static mechanism. The quenching complex was attributed to an interaction between one C — tyrosine rotamer and the disulfide bond. Swadesh et al.(()<>> have studied the dithiothreitol quenching of the six tyrosine residues in ribonuclease A. They carefully examined the steady-state criteria that are useful for distinguishing pure static from pure dynamic quenching by consideration of the Smoluchowski equation(70) for the diffusion-controlled bimolecular rate constant k0,... 

Oxytocin (Pitocin, Syntocinon) causes milk release (letdown) by stimulating contraction of the myoepithelial cells of the milk ducts in lactating mammary glands this forces milk from the alveoli of the breast. Oxytocin release is stimulated by suckling and by auditory and visual stimuli, such as a baby s cry. Oxytocin is available as a nasal spray, which is used as an aid to lactation when milk ejection is impaired. 

Oxytocin Oxytocic (lactation-stimulating) 9 Chemical synthesis... 

Oxytocin is a peptide hormone secreted by the posterior pituitary that participates in labor and delivery and elicits milk ejection in lactating women. During the second half of pregnancy, uterine smooth muscle shows an increase in the expression of oxytocin receptors and becomes increasingly sensitive to the stimulant action of endogenous oxytocin. Pharmacologic concentrations of oxytocin powerfully stimulate uterine contraction. 

Without oxytocin-induced contraction, normal lactation cannot occur. At high concentrations, oxytocin has weak antidiuretic and pressor activity due to activation of vasopressin receptors. 

Vasopressin and oxytocin are peptide hormones secreted from the posterior lobe of the pituitary gland. They function primarily to raise blood pressure (vasopressin), as antidiuretic (vasopressin), and to promote contraction of uterus and lactation muscies (oxytocin). The isolation, identification, and synthesis of these hormones was accomplished by Vincent du Vigneaud, for which he was awarded the Nobel Prize in chemistry in 1955. 

Posterior lobe Antidiuretic hormone [ADH] Oxytocin T renal reabsorption of water t uterine contraction t milk ejection during lactation... 

Estrogens influence the breast tissue at puberty, during each ovulatory cycle, and during pregnancy they participate in duct formation, and, in conjugation with progesterone, oxytocin, and other hormones, prepare the breasts for lactation. 

Oxytocin is usually administered intravenously for stimulation of labor. It is also available as a nasal spray to induce lactation postpartum. It is inactive if swallowed, because it is destroyed in the stomach and intestine. Oxytocin is not bound to plasma proteins and is catabolized by the kidneys and liver, with a circulating half-life of 5 minutes. 

Oxytocin alters transmembrane ionic currents in myometrial smooth muscle cells to produce sustained uterine contraction. The sensitivity of the uterus to oxytocin increases during pregnancy. Oxytocin-induced myometrial contractions can be inhibited by 13-adrenoceptor agonists, magnesium sulfate, or inhalation anesthetics. Oxytocin also causes contraction of myoepithelial cells surrounding mammary alveoli, which leads to milk ejection. Without oxytocin-induced contraction, normal lactation cannot occur. Oxytocin has weak antidiuretic and pressor activity. 

Warfarin sodium may be adsorbed to PVC and intravenous infusion sets but may be minimized with glass containers or polyethylene-lined containers. Warfarin sodium is incompatible with solutions of adrenaline hydrochloride, amikacin sulfate, metaraminol tartrate, oxytocin, promazine hydrochloride, tetracycline hydrochloride, aminophylline, bretylium tosylate, ceftazidime, cimetidine hydrochloride, ciprofloxacin lactate, dobutamine hydrochloride, esmolol hydrochloride, gentamicin sulfate, labetalol hydrochloride, metronidazole hydrochloride, and vancomycin hydrochloride.130131... 

Oxytocin causes contraction of the uterine smooth muscles and stimulates milk ejection in the lactating glands. 

Clarke G, Lincoln DW, Merrick LP (1979) Dopaminergic control of oxytocin release in lactating rats. J Endocrinol 55 409-420. 

Crowley WR, Shyr SW, Kacsoh B, Grosvenor CE (1987) Evidence for stimulatory noradrenergic and inhibitory dopaminergic regulation of oxytocin release in the lactating rat. Endocrinology 121 14-20. 

Crowley WR, Parker SL, Armstrong WE, Grosvenor CE (1991) Excitatory and inhibitory dopaminergic regulation of oxytocin secretion in the lactating rat evidence for respective mediation by D-l abd D-2 dopamine receptor subtypes. Neuroendocrinology 53 493-502. 

Parker SL, Crowley WR (1992) Activation of central D-l dopamine receptors stimulates oxytocin release in the lactating rat evidence for involvement of the hypothalamic paraventricular and supraoptic nuclei. Neuroendocrinology 56 385—392. 

Oxytocin is secreted from the posterior pituitary and targets the uterus (stimulating uterine contraction) and mammary tissue (promoting lactation). The oxytocin receptor couples via a Gas to activate adenylyl cyclase and increase cAMR... 

The administration of systemically acting products via the nasal route began in the 1980s. The peptide oxytocin, which stimulates uterine contraction and lactation, was one of the first nasally administered peptide hormones. Meanwhile, several peptide-based nasal formulations entered the market. Currently, more attention is being paid to this delivery system due to the increasing demands of new highly potent drug formulations. In addition, patients expectations for... 

In 56 women (18-20 weeks gestation), treated at the Marie Stopes Chnic in Jodhpur, India, who underwent termination of pregnancy with 0.1% ethacridine lactate 150 ml injected into the intrauterine extra-amniotic space and in whom intravenous oxytocin was used to expedite the dehvery of the abortus, ethacridine lactate induced successful abortion in 52 cases (1). Abortion failure occurred in the other four cases because of transverse lie of fetus (n = 2), cervical dystocia (n = 1), and uterine inertia (n = 1). In 41 women the abortion occurred at 12-24 hours after induction (mean 20 hours) which was shorter than that of previous reports (29.5-38 hours). There were complications in six cases three women had cervical tears and three had incomplete expulsion. There was one case each of severe bleeding and vaginal laceration. There were no cases of sepsis. The authors concluded that ethacridine lactate performed better than other instillation abortion methods. 

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