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The pituitary contents of oxytocin, vasopressin and α-MSH were measured in fetal and newborn rats to assess possible changes in their release during the process of labour. In the 24 h period during which delivery is likely to occur in the Wistar rat, both the oxytocin and vasopressin content of the fetal pituitary gland increased, whereas α-MSH content remained the same. During and/or just before labour, the oxytocin content was found to decrease by 30%, indicating an enhanced fetal release of the hormone at this stage. It was concluded that the expulsion of each fetus did not provide an extra stimulus for release of oxytocin by the fetus.
In addition, if the fetus remained in the uterus after decapitation of the mother, the oxytocin content of the fetal pituitary gland decreased a further 30%. Neither vasopressin nor 30%. content was altered by the process of labour or by the fetus remaining in the uterus after decapitation of the mother. The levels of vasopressin and α-MSH were, however, 20 times higher than the oxytocin content in the fetus and the newborn, which might have obscured the demonstration of a relatively small change in levels of these two hormones.
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ABSTRACT
Proliferative activity was measured in rat anterior pituitary cells in short-term culture by calculating the labelling index (LI), based on the immunohistochemical detection of cells incorporating the thymidine analogue bromodeoxyuridine. Basal LI was reproducible in the test system. Arginine vasopressin (AVP) induced a dose-related increase in LI up to 20 ng/ml. Corticotrophin-releasing factor-41 (CRF-41) had no effect at doses up to 20 ng/ml. However, in the presence of 10 ng CRF-41/ml, AVP induced a greater increase in LI at lower doses than did AVP alone. Fibroblast growth factor also induced a significant increase in LI. In the system used, epidermal growth factor and insulin had no effect on proliferation.
Journal of Endocrinology (1990) 126, 255–259
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ABSTRACT
In order to assess the physiological importance of endogenous arginine vasopressin (AVP) in augmenting the ACTH response to corticotrophin-releasing factor (CRF), the response to CRF during hypertonic saline infusion in six Coopworth sheep was examined. A 4-h infusion of 5% (w/v) NaCl (3·8 ml/min) resulted in significantly (P < 0·01) greater rises in ACTH and cortisol, but not aldosterone, than were observed after CRF alone. Infusion of hypertonic saline without CRF resulted in a highly significant (P < 0·001) rise in plasma osmolality and AVP but no significant change in plasma ACTH, cortisol or aldosterone.
It is concluded that a marked but physiological increase in peripheral (and presumably central) levels of AVP does not result in any demonstrable change in plasma ACTH concentration. However, under these conditions, the ACTH and cortisol responses to CRF are considerably augmented.
J. Endocr. (1986) 108, 309–312
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The changes which occur in the body-weight of frogs, axolotls, and aquatic reptiles as a result of the injection of vasopressin are generally ascribed to changes in body-water [e.g. Brunn, 1921; Bělehrádek and Huxley, 1927; Heller, 1930; Steggerda, 1931; Steggerda and Essex, 1934; Rey, 1935; Steggerda, 1937; Boyd and Brown, 1938; Boyd and Whyte, 1938; and Boyd and Dingwall, 1939]. The mechanism of the change appears to differ somewhat in different species, but in amphibia it appears to be due both to the increased absorption of water through the skin [Steggerda, 1931] and to antidiuresis [e.g. Rey, 1935; Pasqualini, 1938], with the consequent storage of excess water in muscle, subcutaneous, and other tissues [Steggerda and Essex, 1934; Boyd and Brown, 1938]. In view of the simplicity of the technique necessary to follow gross changes in body-water in these animals, it was of interest to inquire whether or not sex hormones
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Department of Physiology, Charing Cross Hospital Medical School, London, W6
(Received 7 April 1977)
It has been reported (Horrobin, Burstyn, Lloyd, Durkin, Lipton & Muiruri, 1971; Buckman & Peake, 1973; Wallin & Lee, 1976) that prolactin affects salt and water metabolism. To assess any interaction of the antidiuretic hormone arginine-vasopressin (AVP) and prolactin, four experiments were performed.
The antidiuretic action of AVP was measured by the standard AVP bioassay method using the water-loaded ethanol-anaesthetized rat described by Jeffers, Livesey & Austin (1942) with the minor modifications of Forsling, Jones & Lee (1968). Male Wistar rats (150-200 g) were used with at least six preparations for each experiment. When stable antidiuretic responses to standard AVP (3rd International Standard, 1957, National Institute for Biological Standards, London) were obtained, the infusion fluid was changed to one containing the appropriate hormone for the experiment and the effect of AVP within the succeeding hour compared
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Changes in the neurohypophysial content of arginine vasopressin (AVP) and neurosecretory material in different states of hydration have been reported by many authors (see Jones & Pickering, 1969; Vilhardt, 1970). The present paper reports the effect of hydration on pituitary and plasma levels of AVP and neurophysin in the rat, and on the release of these two peptides in response to haemorrhage.
Four groups of male Wistar rats were studied over a period of 1 week. One group was maintained on an unrestricted water intake (control), another on a restricted water intake, the third on 1·8% sodium chloride solution and a fourth group was hydrated (water intake equivalent to 25% body weight/24 h). The rats used weighed 200 g and at least six animals were included in each group. After 1 week the animals were anaesthetized with sodium pentobarbitone (3 mg/100 g) and 0·8 ml blood removed for the determination
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The biological half-life of synthetic, radiochemically pure, biologically active [3H]8-arginine-vasopressin ([3H]AVP), the distribution of radioactivity among the organs and the in-vivo metabolism of the hormone were studied in the rat. The half-life calculated from the [3H]AVP radioactivities isolated from the blood was found to be 1·74 ± 0·22 (s.d.) min in the fast phase, and 16·98 ± 1·01 min in the slow phase. The half-lives of total radioactivity were longer in both phases. The radioactivity accumulated to the greatest extents in the adenohypophysis and small intestine. The radioactive substance was accumulated more by the kidney than by the liver, but the hormone underwent inactivation more quickly in the liver.
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In most species there is a release of oxytocin during the expulsive phase of labour with little or no release during the earlier stages (see Chard, 1972). However, information is lacking on the release of arginine-vasopressin (AVP) during parturition. It appears to be released in the rat (Fuchs & Saito, 1971) but not in the goat (McNeilly, Martin, Chard & Hart, 1972). The present studies demonstrate the release of both oxytocin and AVP during parturition in the horse.
Thirty-one jugular blood samples (20 ml) were collected during labour in three Welsh ponies which produced live foals, 20 samples from three mares in early pregnancy and 25 samples from three mares after elective Caesarean operation. Plasma was separated immediately at 4 °C and stored at -20 °C to obviate enzymic destruction. Oxytocin was determined by radioimmunoassay (Chard, Boyd, Forsling, McNeilly & Landon, 1970) and AVP by bioassay (Forsling, Jones & Lee,
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SUMMARY
The macrolide antibiotic valinomycin decreased short-circuit current (SCC, Na transport) across the isolated bladder of the toad. This effect was not overcome by increasing the K+ levels in the bathing medium or by the action of amphotericin B.
The effects of vasopressin on both sodium and water transfer across the toad bladder were inhibited by valinomycin and the latter inhibition is non-competitive. The action of theophylline in increasing water transfer across the bladder was also inhibited. Cyclic AMP also increased water and Na+ transfer across the bladder but its action was not reduced by the macrolide. These results suggest that valinomycin inhibits adenyl cyclase.
Aldosterone increases sodium transport across the toad bladder and this action was abolished by previous incubation of the tissue with the macrolide. Once the steroid-induced effect had been established subsequent addition of valinomycin did not alter the sodium transfer.
Valinomycin thus appears to have several sites of action on the toad bladder.
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Levels of GH in serum were assayed during the development of heterozygous (HET) control and vasopressin-deficient homozygous (HOM) Brattleboro rats. In early postnatal growth no differences in GH concentrations were present between HET and HOM rats for the rapid decline in serum levels of GH in the first week and the constant period up to day 24 of age thereafter. However, higher values were found in 55-day-old HOM rats and lower values at the age of 9 months. It is concluded that the stunted development of the body and brain of HOM rats is not GH-related, and that changes or anomalies in GH secretion appear only after neurogenesis has been completed.
