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C. Sernia, R. T. Gemmell, and W. G. Thomas

ABSTRACT

There is inconclusive evidence that oxytocin acts directly on the corpus luteum and affects steroidogenesis. Since any such action would probably be mediated by oxytocin receptors, these should be present in luteal tissue. In this study, homogenates of corpora lutea from both pregnant and non-pregnant ewes were examined for oxytocin receptors by radio-receptor assay. Specific oxytocin binding was not observed in luteal tissue during the oestrous cycle. However specific binding was found in the corpora lutea of pregnant ewes; appearing at a fetal head length of approximately 0·65 cm (about 30 days of pregnancy) and persisting to a head size of 11 cm, the largest size examined in this study. The affinity (K d) of the receptor was calculated as 2·9 ± 0·3 nmol/l (s.e.m.; n = 9), a value similar to that obtained for the uterus. The receptor number ranged from a low of 8·7± 3·2 fmol/mg protein (n = 6) at a head size of <0·65 cm, to a maximum of 40·1 ± 6·5 fmol/mg protein (n = 25) at a head size of 2·5–3·75 cm. These values were lower than our estimate of 588 ± 39 fmol/mg protein (n = 5) for the uterus. It is concluded that a direct action of oxytocin on the corpus luteum is possible but only after the first month of pregnancy and not in the corpus luteum of the oestrous cycle.

Journal of Endocrinology (1989) 121, 117–123

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SANDRA M. EGAN and A. LIVINGSTON

SUMMARY

Tissue uptake of oxytocin by rat mammary gland, uterus, heart and skeletal muscle was demonstrated by incubation of these tissues with 3H-labelled oxytocin. Chromatography of tissue extracts showed that some breakdown of oxytocin had occurred after only 30 s. However, in all cases there was no breakdown of oxytocin in the corresponding incubation medium. This indicated that the breakdown of oxytocin occurred within the tissues.

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R J Windle, J M Judah, and M L Forsling

Abstract

The effect of three oxytocin receptor antagonists on the renal actions of oxytocin and vasopressin was investigated in conscious male rats infused with hypotonic saline. Infusion of oxytocin at 100 pg/min produced plasma concentrations of 12·7 ± 3·3 pmol/l and led to significant increases in sodium excretion, urine flow and glomerular filtration rate (GFR). The increase in sodium excretion of 42 ± 9% during oxytocin infusion was significantly decreased by all three antagonists to 15 ± 5% (10 ng [mercapto-proprionic acid1,d-Tyr(Et)2, Thr4,Orn8]-oxytocin/min), 13 ± 5% (5 ng desGly9[d-Trp2,Thr4,Orn8]-dC6oxytocin/min) and 4 ± 5% (1 ng d(CH2)5[Tyr(Me)2,Thr4,Orn8,Tyr(NH2)9]-vasotocin/min). Similarly, the increase in urine production of 22 ± 5% associated with oxytocin infusion was significantly decreased to 4 ± 3% (5 ng desGly9[d-Trp2,d-Thr4,Orn8]-dC6oxytocin/min) and 1 ± 4% (1 ng d(CH2)5[Tyr(Me)2,Thr4,Orn8,Tyr(NH2)9]-vasotocin/min). All three antagonists blocked the oxytocin-induced increase in GFR when infused at 10 ng/min. Infusion of vasopressin at 160 pg/min produced plasma concentrations of 10·1 ± 2·1 pmol/l and this led to a significant increase in sodium excretion and a significant decrease in urine flow rate. None of the antagonists had any effect on the natriuretic or antidiuretic actions of vasopressin suggesting that different receptors are involved in these renal actions of the two peptides.

Journal of Endocrinology (1997) 152, 257–264

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N. R. H. BOYD, D. B. JACKSON, STELLA HOLLINGSWORTH, MARY L. FORSLING, and T. CHARD

SUMMARY

A method is described for the extraction and concentration of oxytocin from urine, satisfactory for the radioimmunoassay of this peptide. The recovery of added oxytocin was 64·8 ± 12·6 (s.d.)% from urine samples with an osmolality less than 770 mosm./kg, and 44·9 ± 13·5% for urine samples of greater osmolality. Infusions of oxytocin at a rate of 1 mu./min into male and female volunteers showed a direct relationship between the volume of urine and the total amount of oxytocin excreted during any 1-h period. Extracts of normal male urine contained an immunoreactive material which behaved identically with synthetic oxytocin in two systems of chromatography.

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J J Evans

Introduction

The idea that oxytocin can control luteinizing hormone (LH) is not new, and has always been intriguingly controversial. This paper will discuss some of the reasons for the confusion and consider the emerging evidence that indicates an important role in regulating gonadotrophins for oxytocin. Both prior and subsequent to the definition of the classical hypothalamic-releasing factors the possibility that the hormones from the posterior lobe of the pituitary gland had roles as additional regulators in anterior pituitary gland hormone secretion was also investigated (Martini & Morpurgo 1955, Benson & Folley 1957, McCann 1957). The anatomical proximity of the two lobes of the pituitary gland and the reports of evidence for direct portal communication between them (Baertschi 1980) pointed to the potential for interactions. In addition, nerve fibres from the hypothalamus were observed to terminate on the hypophysial portal vessels (Silverman 1976, Zimmerman & Antunes 1976). For at least four

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D. F. SWAAB and C. W. POOL

Netherlands Central Institute for Brain Research, Ijdijk 28, Amsterdam0, The Netherlands

(Received 6 November 1974)

INTRODUCTION

Although immunohistochemistry is considered to provide a specific and sensitive tool for the localization of hypothalamic hormones (Zimmerman, Hsu, Ferin & Koslowski, 1974), attempts to localize vasopressin and oxytocin by immunofluorescence have raised questions about the specificity of this technique. Homozygous Brattleboro rats were used in our experiments as a control for vasopressin immunofluorescence since their hypothalamo-neurohypophysial system (HNS) does not contain any measurable amount of this hormone (Valtin, Sawyer & Sokol, 1965). Despite this, bright fluorescence was observed in the HNS of these animals, not only using antibodies against oxytocin, but also with all tested antibodies raised against lysine- or arginine-vasopressin. In addition, immunofluorescence was observed beyond the HNS of Wistar and heterozygous Brattleboro rats, i.e. in the suprachiasmatic nucleus.

Because of these findings and the fact that the commonly used

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F. Moos, M. J. Freund-Mercier, Y. Guerné, J. M. Guerné, M. E. Stoeckel, and Ph. Richard

ABSTRACT

The release of endogenous oxytocin and vasopressin by rat paraventricular and supraoptic nuclei in vitro during a 10-min period, 30 min after beginning the incubation, was measured radioimmunologically. Mean basal hormone release per 10 min and per pair of nuclei was: 128·4 ± 12·4 (s.e.m.) pg vasopressin (n = 15) and 39·0 ± 3·0 pg oxytocin (n = 66) for supraoptic nuclei from male rats; 273·9 ± 42·6 pg vasopressin (n = 11) and 34·2 ± 3·5 pg oxytocin (n = 15) for supraoptic nuclei from lactating rats; 70·0 ± 8·6 pg vasopressin (n = 52) and 21·8 ± 1·3 pg oxytocin (n = 68) for paraventricular nuclei from male rats; 59·1 ± 8·6 pg vasopressin (n = 10) and 27·0 ± 4·6 pg oxytocin (n = 16) for paraventricular nuclei from lactating rats.

In male and lactating rats, both nuclei contained and released more vasopressin than oxytocin. For oxytocin alone, the paraventricular nucleus of male rats contained and released significantly less hormone than the supraoptic nucleus. This difference was not apparent in lactating rats. For vasopressin alone, the paraventricular nucleus contained and released significantly less hormone than the supraoptic nucleus in both male and lactating rats. When the hormone released was calculated as a percentage of the total tissue content the release was about 0·9% for oxytocin from both nuclei in male and lactating rats and also for vasopressin in lactating rats, but was only about 0·5% for vasopressin from both nuclei in male rats.

The influence of oxytocin and analogues of oxytocin (including one antagonist) upon the release of oxytocin and vasopressin was studied. Adding oxytocin to the incubation medium (0·4–4 nmol/l solution) induced a dose-dependent rise in oxytocin release from both nuclei of male or lactating rats. A 4 nmol/l solution of isotocin had a similar effect to a 0·4 nmol/l solution of oxytocin, but arginine-vasopressin never affected basal release of oxytocin. In no case was vasopressin release modified.

An oxytocin antagonist (1 μmol/l solution) significantly reduced basal oxytocin release and blocked the stimulatory effect normally induced by exogenous oxytocin, as did gallopamil hydrochloride (D600, 10 μmol/l solution), a Ca2+ channel blocker, or incubation in a Ca2+-free medium.

These findings are discussed in relation to the literature on the central effects of neurohypophysial peptides. It may be concluded that the regulatory role of endogenous oxytocin in the hypothalamus on the milk-ejection reflex could result from its local release in the extracellular spaces of magnocellular nuclei.

J. Endocr. (1984) 102, 63–72

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E Houdeau, A Lévy, and S Mhaouty-Kodja

role in the regulation of uterine contractility. Indeed, contractant factors like oxytocin (OT), prostaglandins or norepinephrine utilize PLC-coupled receptors (OT receptors (OTR), prostaglandin F2α receptors (FP) and α1-adrenergic receptors (AR

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F S Khan-Dawood, J Yang, K Anwer, and M Y Dawood

Abstract

Oxytocin has been identified in both non-human primate and human corpora lutea of the menstrual cycle by RIA, immunocytochemistry and HPLC. Evidence for the transcription of the oxytocin gene in this tissue using PCR is available. Oxytocin receptors have been characterized by biochemical procedures. However, there is some debate as to whether the oxytocin identified in these tissues is biologically active and has a role in luteal function. In this study we have demonstrated that oxytocin isolated by gel chromatography of tissue extracts from the baboon and the human corpus luteum is biologically active as determined in a rat uterine bioassay. Since both oxytocin and its receptors are present in these tissues, it is suggested that oxytocin in the human and non-human primate corpora lutea has a functional role.

Journal of Endocrinology (1995) 147, 525–532

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T. CHARD

The first radioimmunoassay was described by Yalow & Berson in 1960, since when the technique has been widely used in physiological and patho-physiological studies of the protein hormones. The success in this field has led to a number of attempts to develop similar assays for the small peptide hormones (molecular weight less than 3000). However, these compounds present certain difficulties which have considerably retarded progress. The purpose of the present review is to discuss the problems of the radioimmunoassay of the neurohypophysial peptides, with particular reference to oxytocin and vasopressin.

The problems of the radioimmunoassay of small peptide hormones

There are two major problems. (1) Being of low molecular weight (about 1000) they are poor immunogens. As a result, the preparation of high-affinity antisera is considerably more exacting than in the case of larger molecules. (2) Their levels in the circulation are, in molar terms, considerably lower than those of