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Lucia Gajdosechova, Katarina Krskova, Ana Belen Segarra, Andrea Spolcova, Maciej Suski, Rafal Olszanecki, and Stefan Zorad

Introduction The neuropeptide oxytocin is a hormone with a wide range of central and peripheral effects. Besides its well-known role in labour and lactation ( Gimpl & Fahrenholz 2001 ), oxytocin is released in response to various stress stimuli

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Gareth Leng, Rafael Pineda, Nancy Sabatier, and Mike Ludwig

stimulation of the neural stalk in lactating rabbits resulted in a sharp rise in intramammary pressure, and they inferred that this was the consequence of oxytocin secreted from the posterior pituitary. They noted that the response to stimulation depended

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Mone Zaidi, Maria I New, Harry C Blair, Alberta Zallone, Ramkumarie Baliram, Terry F Davies, Christopher Cardozo, James Iqbal, Li Sun, Clifford J Rosen, and Tony Yuen

Argiolas A Collu M Gessa GL Melis MR Serra G 1988 The oxytocin antagonist d(CH2)5Tyr(Me)-Orn8-vasotocin inhibits male copulatory behaviour in rats . European Journal of Pharmacology 149 389 – 392 . ( https://doi.org/10

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Tatiane Vilhena-Franco, André Souza Mecawi, Lucila Leico Kagohara Elias, and José Antunes-Rodrigues

experimental model extensively used to study these responses. WD increases osmolality and decreases plasma volume, inducing the release of hormones that act to maintain homeostasis, such as vasopressin (AVP) and oxytocin (OT), and the activation of the renin

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Eriko Furube, Tetsuya Mannari, Shoko Morita, Kazunori Nishikawa, Ayaka Yoshida, Masanobu Itoh, and Seiji Miyata

arginine vasopressin (AVP) and oxytocin (OXT) into the blood circulation from their axonal terminals ( Miyata & Hatton 2002 ). Similarly, they release a variety of neuropeptides into the blood circulation at the median eminence (ME) to control secretion of

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M. Y. DAWOOD, K. S. RAGHAVAN, and C. POCIASK

The evaluation of a radioimmunoassay of oxytocin is described. The method involved careful collection and transportation of blood at 4 °C, acidification of the plasma, extraction with Fuller's earth and radioimmunoassay using antisera raised in rabbits immunized against oxytocin conjugated to bovine serum albumin and 125I-labelled oxytocin. The antisera showed insignificant cross-reaction with a variety of small peptides including vasopressin and vasotocin. The limit of detection of the assay was 2·5 pg with intra-assay and interassay coefficients of variation of 7–15% and 12–18% respectively. Seventy-seven per cent (88 out of 116) of the pregnant women tested had detectable maternal plasma oxytocin. Serial samples of maternal plasma showed a significant increase in oxytocin from the first to the second stage of labour and a significant decrease in the third stage. Oxytocin concentrations in the umbilical arterial plasma were significantly higher in patients in labour. The significance of these findings is discussed.

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EWA BRZEZIŃSKA-ŚLEBODZIŃSKA

SUMMARY

The oxytocin-inactivating activity (OIA) of liver, kidney, uterus, pancreas, spleen and duodenum homogenates of hens was studied. The first-order constant of oxytocin inactivation was higher in the liver and pancreas than in the uterus and kidney or in the duodenum and spleen. Using synthetic analogues of oxytocin (deamino-oxytocin, deamino-carba1-oxytocin and carba1-oxytocin the mechanism of enzymic inactivation of oxytocin by hen tissue was investigated.

Enzymic hydrolysis by the CH2-terminal cleavage was most marked in duodenum (about 86% OIA) and kidney (54·8% OIA). Reduction of the disulphide bridge was most marked in the uterus (about 80% OIA) and pancreas (about 73% OIA). Splitting by non-specific aminopeptidases after reduction of the disulphide bridge occurred mainly in the liver (72% OIA) and in the spleen (44% OIA).

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H. D. Nicholson, S. E. F. Guldenaar, G. J. Boer, and B. T. Pickering

ABSTRACT

The long-term effects of oxytocin administration on the testis were studied using intratesticular implants. Adult male rats had an Accurel device containing 20 μg oxytocin (releasing approximately 200 ng/day) implanted into the parenchyma of each testis; control animals received empty devices. The animals were killed at weekly intervals for 4 weeks. Some animals were perfused and the testes processed for light and electron microscopy. Blood was collected from the remaining animals for the measurement of testosterone, dihydrotestosterone, LH, FSH and oxytocin; epididymal sperm counts were measured and the testes were extracted and radioimmunoassayed for testosterone, dihydrotestosterone and oxytocin.

Long-term administration of oxytocin resulted in a significant reduction in testicular and plasma testosterone levels throughout the 4-week period examined and, after 14 days of treatment, lipid droplets were seen in the Leydig cells of treated but not control animals. Concentrations of dihydrotestosterone in the plasma and testes of the oxytocin-treated animals, however, were significantly elevated after 7 and 14 days and at no time fell below control values. Plasma FSH levels were also lower in the oxytocin-treated animals. Intratesticular oxytocin treatment did not affect LH or oxytocin concentrations in the plasma, epididymal sperm counts or the number of Leydig cells in the testis. Empty Accurel devices had no effect on testicular morphology.

This study provides the first evidence that oxytocin in vivo can modify steroidogenesis in the testis.

Journal of Endocrinology (1991) 130, 231–238

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R. G. Dyer

Every physiology student is taught that oxytocin is released from the neurohypophysis and acts on the myoepithelial cells to effect milk ejection and on the myometrium to elicit uterine contractions. Milk ejection requires the bolus release of oxytocin, by the (approximately) synchronous discharge of the magnocellular oxytocin containing neurones in the hypothalamus, and this is initiated reflexly by the suckling stimulus applied to the nipple. During parturition also, oxytocin can be released as part of a neuroendocrine reflex when the fetus stimulates sensory nerve endings during its passage through the cervix. The reflex release of oxytocin at this time greatly aids the rapid completion of the delivery process.

All of the foregoing has been known for years and some of it for decades. During this time little progress was made in identifying any clearly defined physiological role for oxytocin during the earlier stages of parturition. Indeed maturational processes in the

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Hiroki Otsubo, Susumu Hyodo, Hirofumi Hashimoto, Makoto Kawasaki, Hitoshi Suzuki, Takeshi Saito, Toyoaki Ohbuchi, Toru Yokoyama, Hiroaki Fujihara, Tetsuro Matsumoto, Yoshio Takei, and Yoichi Ueta

vasopressin (AVP; Yokoi et al . 1996 ). Central administration of AM activated oxytocin (OXT)-secreting neurones in the supraoptic (SON) and the paraventricular nuclei (PVN; Serino et al . 1999 , Ueta et al . 2000 ), and markedly increased plasma OXT