Oxytocin differences

The primary structures of the pituitary hormones vasopressin and oxytocin differ by Just two amino acids, ... 

Ergometrine and oxytocin differ in their actions on the uterus. In moderate doses oxytocin produces slow generalised contractions with full relaxation in between ergometrine produces faster contractions superimposed on a tonic contraction. High doses of both substances produce sustained tonic contraction. It will be seen, therefore, that oxytocin is more suited to induction of labour and ergometrine to the prevention and treatment of postpartum haemorrhage, the incidence of which is reduced by its routine prophylactic use (generally i.m.). 

AVP), except in the pig which has a Lys residue (iysine vasopressin). Oxytocin differs from vasopressin in having leucine at position 8 and isoleucine at position 3. Vasopressin and oxytocin analogues with some degree of receptor subtype selectivity that have been synthesized have ANTIDIURETIC or vasoconstrictor or OXYTOCIC (uterine-contracting) activity. See VASOPRESSIN RECEPTOR AGONISTS VASOPRESSIN RECEPTOR ANTAGONISTS. 

Bradykinin, vasopressin, and oxytocin are peptide hormones. They are all nonapeptides. Bradykinin inhibits the inflammation of tissues. Vasopressin controls blood pressure by regulating the contraction of smooth muscle. It is also an antidiuretic. Oxytocin induces labor in pregnant women and stimulates milk production in nursing mothers. Vasopressin and oxytocin both have an intrachain disulfide bond, and their C-terminal amino acids contain amide rather than carboxyl groups. Notice that the C-terminal amide group is indicated by writing NH2 after the name of the C-terminal amino acid. In spite of their very different physiological effects, vasopressin and oxytocin differ only by two amino acids. 

Figure 9.2 The structures of vasopressin and oxytocin. Differences are in amino acid residues 3 and 8. The normal carboxylate groups of the C-terminal residues (Gly) have been replaced by amide groups.

Oxytocin, which is produced in the pituitary gland, causes the contraction of smooth muscle, including the uterus. It is used clinically to induce labor or to increase the strength of uterine contractions. Vasopressin, another pituitary hormone, regulates the secretion of water by the kidneys and affects blood pressure. The structures of vasopressin and oxytocin differ by only two amino acids. They are cyclic peptides that are hnked by a disulfide bond between two cysteine residues. 

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). 

Oxytocin also exerts its major effects on two different target tissues. This hormone stimulates ... 

Similarly, though plasma protein binding data were not ostensibly used in the identification of an oxytocin antagonist suitable for advancement to the clinic, such data were used to explain the differences between in vivo and in vitro potency [46]. 

Nissen, E., Uvnas-Moberg, K., Svensson, K., Stock, S, Widstrom, A. M., and Winberg, J. 1996. Different patterns of oxytocin, prolactin but not cortisol release during breast feeding in women delivered by caesarean section or by the vaginal route. Early Human Development, in press. 

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 . 

Lakowicz et al.(]7] VB) examined the intensity and anisotropy decays of the tyrosine fluorescence of oxytocin at pH 7 and 25 °C. They found that the fluorescence decay was best fit by a triple exponential having time constants of 80, 359, and 927 ps with respective amplitudes of 0.29, 0.27, and 0.43. It is difficult to compare these results with those of Ross et al,(68) because of the differences in pH (3 vs. 7) and temperature (5° vs. 25 °C). For example, whereas at pH 3 the amino terminus of oxytocin is fully protonated, at pH 7 it is partially ionized, and since the tyrosine is adjacent to the amino terminal residue, the state of ionization could affect the tyrosine emission. The anisotropy decay at 25 °C was well fit by a double exponential with rotational correlation times of 454 and 29 ps. Following the assumptions described previously for the anisotropy decay of enkephalin, the longer correlation time was ascribed to the overall rotational motion of oxytocin, and the shorter correlation time was ascribed to torsional motion of the tyrosine side chain. 

Fig. 3A, B Neuropeptide effects on anxiety-related behavioiu. A The oxytocin receptor antagonist (black bars) administered intracerebroventricularly (i.c.v.) increased indices of anxiety-related behaviour in pregnant rats as measured on the elevated plus maze. Entries into the closed arms indicate unchanged locomotor activity. B Prolactin is an anxiolytic neuropeptide in female rats as revealed by i.c.v. administration of synthetic prolactin (grey and black bars represent two different doses) and by antisense targeting of the prolactin receptor (R). Vehicle (white bars) vs mixed bases (grey bars) and antisense oligodeoxynu-cleotide (black bars). p<0.05 vs vehicle (white bars). (Adapted from Nemnann et al. 2000) and Torner et al. 2001)...

Unlike AVP, oxytocin does not seem to be involved in trait anxiety, as its expression and release in the PVN did not differ between HAB and LAB rats (Wigger et al. 2004). 

Antidiuretic hormone (ADH) and oxytocin are synthesized in the supraoptic and paraventricular nuclei in the brain and are transported in secretory granules through axons to the posterior lobe. These hormones are cyclic peptides of eight amino acids. Each is synthesized as a larger precursor, which is processed into the hormone plus a protein that binds the hormone, called neuro-physin. ADH and oxytocin have different amino acids at positions 3 and 8. 

A. General description Oxytocin is a nonapeptide (molecular weight 1.0 kDa) that differs by two amino acids from vasopressin it is stored and released from the posterior pituitary gland. Commercially available oxytocin is prepared synthetically. 

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