Oxytocin functions

Oxytocin and Vasopressin Receptors. The actions of oxytocin and vasopressin are mediated through their interactions with receptors. Different receptor types as well as different second messenger responses help explain their diverse activities in spite of the hormones stmctural similarities. Thus oxytocin has at least one separate receptor and vasopressin has been shown to have two principal receptor types, and V2. Subclasses of these receptors have been demonstrated, and species differences further compHcate experimental analysis. It is apparent that both oxytocin and receptors function through the GP/1 phosphoHpase C complex (75), while the V2 receptors activate cycHc AMP (76). 

Vasopressin and Oxytocin. Arginine -vasopressin (AVP, vasopressia also known as antidiuretic hormone, ADH) (342) is a nonapeptide amide that functions both as a neuroregulator and a hormone (84,85). Oxytocia (OT) (343) is a nonapeptide amide related to AVP. 

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 ... 

Gimpl G, Fahrenholz F (2001) The oxytocin receptor system structure, function, and regulation. Physiol Rev 81 629-683... 

Ephedra (sea grape, ma-huang, yellow horse) ephedra sinica Relieves colds, improves respiratory function, headaches, diuretic effects 3heart rate, psychosis l hedra should only be used after consulting with the physician. Many restrictions apply and the herb can cause serious reactions. Do not use with cardiac glycosides, monoamine oxidase inhibitor halothane, guanethidine, (MAOIs) or oxytocin. Do not use with 3. John s wort or in weight loss formulas. 

Vasopressin is closely related to oxytocin and both peptides are cyclic in that they contain a disulphide bridge. Although much is known about the peripheral actions of the peptides the extent of our current knowledge of their possible CNS function is that vasopressin appears to act as a cognitive enhancer and has positive effects on learning processes in animals. Vasopressin acts on three receptors, Via and b and a V2 receptor. 

A benzodiazepine template was also reported by researchers at GlaxoSmithKline [85]. The lead molecule GW405212, (40), was identified from a 1,296-member library of 1,4-benzodiazepines prepared on Tentagel beads and screened initially in pools of 30 against CHO cells expressing the human oxytocin receptor. It is a highly potent inhibitor of oxytocin binding with a K of 8nM [86]. However, all attempts to improve the pharmacokinetic properties of this molecule were unsuccessful. It appears that the functionality responsible for the oxytocin activity is distributed around the periphery... 

Luteolysis The structural and functional degradation of the corpus luteum that occurs at the end of the luteal phase in the absence of pregnancy caused by the hormones prostaglandin-2(X and oxytocin. Communication between the corpus luteum and uterine endometrium is necessary for luteolysis. 

Grazzini E, Guillon G, Mouillac B, Zingg HH. Inhibition of oxytocin receptor function by direct binding of progesterone. Nature 1998 392 509-512. 

Ryanodine receptors can be blocked by exposing the cells to 10 /iM ruthenium red. Under these conditions, oxytocin exposure still elicits Ca2+ waves, and the observed wave speeds are the same as waves measured in the absence of ruthenium red (Young Zhang 2001). Thus, similarly to InsP3 receptors, functional ryanodine receptors are not rate limiting in the mechanism of Ca2+ wave propagation. 

The effects of both oxytocin and vasopressin are particularly responsive to reproductive steroids (Tables 7 and 8). Oxytocin and vasopressin are best known as neurohypophyseal peptides, released by the posterior pituitary. However, both peptides also are released within the nervous system. Receptors for oxytocin and vasopressin are distributed in areas of the CNS that have been implicated in reproduction, emotion and autonomic functions. 

Oxytocin is important in parasympathetic function (Uvnas-Moberg, 1996), and particularly the control of subdiaphragmatic vagal activity (Porges, 1996). Specific brainstem nuclei... 

Oxytocin, a peptide which initiates uterine contractions during labour is identical in structure to ADH except at position 8 where a leucine residue replaces arginine. The close structural similarity but radically different biological functions, illustrate how specific some hormone receptors are in recognising only their own signal . 

Brussaard AB, Herbison AE (2000) Long-term plasticity of postsynaptic GABAA-receptor function in the adult brain insights from the oxytocin neurone. Trends Neurosci 23 190-195... 

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... 

Legros JJ (2001) Inhibitory effects of oxytocin on corticotrope function in humans are vasopressin and oxytocin ying-yang neurohormones Psychoneuroendocrinology 26 649-655... 

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