Oxytocin secretion

Bruhn TO, Sutton SW, Plotsky PM, Vale WW (1986) Central administration of corticotropinreleasing factor modulates oxytocin secretion in the rat. Endocrinology 119 1558-1563... 

Joigensen H, Riis M, Knigge U, Kjaer A, Warbeig J. Serotonin receptors involved in vasopressin and oxytocin secretion. J Neuroendocrinol 2003 15 242-249. 

The function of oxytocin is to cause uterine contraction and the release of milk from the mammary glands. As with prolactin, suckling, via the neural pathways, induces oxytocin secretion by the neurohypophysis. Blood oxytocin levels increase greatly just before parturition. Oxytocin is used as a drug to induce labor in pregnant women at term. 

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. 

Cunningham ET, Sawchenko PE (1991) Reflex control of magnocellular vasopressin and oxytocin secretion. 

Stricker EM, Verbalis JG. Central inhibitory control of sodium appetite in rats correlation with pituitary oxytocin secretion. Behav Neurosci 1987 101 560-567. 

Voss, AK., Be Fortune, J.E. (1993). Estradiol-17-b has a biphasic effect on oxytocin secretion by bovine granulose cells. Biol. Reprod., 48, 1404—1409. 

Stimuli for oxytocin secretion include sensory stimuli arising from dilation of the cervix and... 

Kadowaki, K., Kishimoto, J., Leng, G., and Emson, P. C. (1994). Up-regulation of nitric oxide synthase (NOS) gene expression together with NOS activity in the rat hypothalmo-hypophysial system after chronic salt loading—Arginine vasopressin and oxytocin secretion. Endocrinology (Baltimore) 134, 1011-1017. 

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 ... 

Outside the uterus, oxytocin has long been known to be essential for milk secretion. In recent years, however, there has also been a growing body of evidence that oxytocin plays a role in the brain in modulation of maternal, sexual and social behaviour. 

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 hypothalamic releasing factors regulate release of the anterior pituitary trophic hormones. As summarized in Figure 52-1, the releasing factors are produced in various neuronal groups within the hypothalamus and are transported to the median eminence for release into the portal circulation to the anterior pituitary. Neurons in the hypothalamus also produce the hormones oxytocin and vasopressin, which are released by the posterior pituitary into the blood. Therefore, it is not surprising that behavior and experience, which influence the hypothalamus, sometimes alter the secretion of these hypothalamic releasing factors and hormones. 

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,... 

Posterior pituitary Two hormones, vasopressin and oxytocin, are synthesised in the hypothalamus and then transported through nerve axons to the posterior pituitary, where they are stored until released. Vasopressin acts on the kidney to conserve water. Its secretion is stimulated by thirst and a decrease in blood pressure. Secretion of oxytocin initiates uterine contraction for parturition. It also stimulates milk ejection from the mammary glands. 

Pituitary Posterior part secretes hormones produced by the hypothalamus, e.g., antidiuretic hormone, oxytocin... 

Altemus M, Cizza G, Gold P (1992) Chronic fluoxetine treatment reduces hypothalamic vasopressin secretion in vitro. Brain Res 593 311-313 Appenrodt E, Schnabel R, Schwarzberg H (1998) Vasopressin administration modulates anxiety-related behavior in rats. Physiol Behav 64 543-547 Arborelius L, Owens MJ, PlotskyPM, Nemeroff CB (1999) The role of corticotropin-releasing factor in depression and anxiety disorders. J Endocrinol 160 1-12 Argiolas A, Gessa GL (1991) Central functions of oxytocin. Neurosci Biobehav Rev 15 217-231... 

Oxytocin (OT) is a nonapeptide in which six amino acids form a ring closed by a disulfide bridge, while the ring itself forms an antiparallel pleated sheet. The tail portion of the peptide, composed of Pro-Leu-Gly-NHj, is also rigidly held in a folded conformation. Oxytocin causes the powerful contraction of some smooth muscles and plays a vital role in milk ejection (not to be confused with milk secretion, which is regulated by prolactin). It also has uterotonic action, contracting the muscles of the uterus, and is therefore used clinically to induce childbirth. 

The anterior lobe secretes various trophic hormones, the posterior lobe is responsible for the secretion of oxytocin and antidiuretic hormone (vasopressin) and middle lobe secretes melanocyte-stimulating hormone (MSH) which may affect the synthesis of melanin. 

The posterior lobe secretes two hormone namely oxytocin and antidiuretic hormone (ADH or vasopressin). 

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. 

Many small peptides exert their effects at very low concentrations. For example, a number of vertebrate hormones (Chapter 23) are small peptides. These include oxytocin (nine amino acid residues), which is secreted by the posterior pituitary and stimulates uterine contractions bradykinin (nine residues), which inhibits inflammation of tissues and thyrotropin-releasing factor (three residues), which is formed in the hypothalamus and stimulates the release of another hormone, thyrotropin, from the anterior pituitary gland. Some extremely toxic mushroom poisons, such as amanitin, are also small peptides, as are many antibiotics. 

OXYTOCIN. A polypeptide hormone which is secreted by the posterior lobe of the pituitary gland of mammals and other vertebrates. Oxytocin exerts a stimulating effect upon the muscles of the breast (milk-ejection) and those of the uterus of mammals. It is sometimes used medically to stimulate labor in cases of difficult childbirth and to time the onset of labor. 

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