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The mean rate of excretion of neurophysins in the urine of 16 patients with kidney disease but without tubular dysfunction was 0·48 ± 0·14 (s.e.m.) ng/min, whereas the rate in 16 patients with tubular dysfunction was 3·64 ± 1·56 ng/min (significantly different; 2P < 0·01). In the whole group of 32 patients there was a relationship (r = 0·57) between the rate of excretion of neurophysins in the urine and the clearance of lysozyme. The increased rate of urinary excretion of neurophysins observed in some patients with kidney disease therefore appears to be related to a disorder of renal tubular function. It is shown that the raised levels of neurophysins observed in the serum of some patients with kidney disease are not attributable to a decrease in the urinary clearance of neurophysins.
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SUMMARY
An almost specific release of neurophysin II with only minor release of neurophysin I was found during venous or arterial haemorrhage in five cows. Our data confirm the results of experiments in vitro in which vasopressin has been found to be associated with neurophysin II within neurosecretory granules.
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SUMMARY
Using continuous blood sampling a specific release of neurophysin I without a significant release of neurophysin II was found during hand-milking and suckling in seven out of eight cows. Hand-milking appeared to be a slightly more powerful stimulus than suckling.
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*Howard Florey Institute of Experimental Physiology and Medicine, Melbourne, Victoria, Australia and † Radioimmunoassay Laboratory, University of Liège, B-4000 Liège, Belgium
(Received 8 July 1976)
The nonapeptide, arginine-vasotocin (AVT, mol. wt 1050) present in the pineal gland of mammals, including man (Milcu, Pavel & Neacsu, 1963; Pavel, 1973; Legros, Louis, Demoulin & Franchimont, 1976) has been shown to reduce gonadotrophin secretion in vivo (Pavel & Petrescu, 1966; Cheesman & Fariss, 1970; Vaughan, Vaughan & Reiter, 1975). When injected into the third ventricle in doses of 0·5 μu. (1 pg), AVT has been shown to inhibit compensatory ovarian hypertrophy in the mouse (Pavel, Petrescu & Vicoleanu, 1973). However, when used in pharmacological doses (2–50 μg) AVT did not inhibit pregnant mare serum-human chorionic gonadotrophin-induced ovulation response in the mouse (Cheesman & Forsham, 1974). Comparable doses were also found to be ineffective in altering the secretion of gonadotrophins from rat anterior hemipituitary
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University of Liège, Department of Internal Medicine, Radioimmunoassay Laboratory, Boulevard Piercot 23, B-4000 Liège, Belgium
(Received 20 October 1975)
The human foetal pineal contains (Pavel, Dumitru, Klepsh & Dorcescu, 1973 b) and synthesizes (Pavel, Dorcescu, Petrescu-Holban & Ghinea, 1973 a) arginine-vasotocin (AVT) which could be the physiological antigonadotrophic factor (Pavel et al. 1973 b). Neurophysins, the carriers of vasopressin (ADH) and oxytocin along the hypothalamo-neurohypophysial tract have been isolated from bovine pineal glands (Reinharz, Czernichow & Vallotton, 1974) and identified in one human pineal tumour (Legros, Louis, Grotschel-Stewart & Franchimont, 1975). In the latter study we showed that AVT was present in 'free form' unbound to neurophysins. Here we confirm the presence of immunoreactive neurophysins and AVT in the normal foetal pineal.
Five glands were removed as rapidly as possible after therapeutic abortion, immediately put in cold acetone and later homogenized in 1ml NaCl (0·9%) by ultrasonication. After centrifugation (4,200g,
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Neurophysin is considered to act as a carrier protein for oxytocin and arginine vasopressin (AVP) in the neurohypophysis, and recent evidence has suggested that neurophysin is released into the blood together with the neurohypophysial hormones in response to various stimuli (Cheng & Friesen, 1970). Neurophysin, extracted from bovine pituitary posterior lobes, consists of two major components designated neurophysin I and II (Hollenberg & Hope, 1968) both of which bind oxytocin and AVP in vitro, although neurophysin II appears to be located specifically in neurosecretory granules containing AVP (Dean, Hope & Kazie, 1968).
We now report results relating to the release of neurophysin, oxytocin and vasopressin into the blood in response to hand-milking, mating and haemorrhage in the goat. Consecutive serial blood samples (approximately 25 ml each) were taken from an indwelling jugular cannula during hand-milking in one goat and during mating in four oestrous female goats (McNeilly & Folley, 1970).
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SUMMARY
Bovine neurophysin I and neurophysin II (bNpI and bNpII) have been assayed by radioimmunoassay in the jugular venous blood of cows during parturition.
In general, low bNpI levels were detected on the day before labour began and during the first stage of labour. Neurophysin I was present in appreciable quantities in blood taken during the second stage of labour and in most cows the concentrations rose to a maximum during the expulsive stage. After delivery, the concentration of bNpI in the blood diminished. This pattern of release is similar to that reported for oxytocin at parturition in cows.
As with bNpI, maximum levels of bNpII occurred during the expulsive stage of labour in some animals. In others, bNpII concentrations were very low or absent. Low concentrations of bNpII were found at the other stages of labour. Examination of the results from individual animals indicated that the release of the two neurophysins can be independent.
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The kinetics of 131I-labelled insulin distribution in heart, liver, kidneys and urinary bladder of rabbits were studied in vivo by gamma-camera techniques combined with plasma measurements (glucose concentrations and chromatographic separation of insulin and its degradation products). The distribution space of radioiodinated insulin differed from the vascular bed delineated by radioiodinated serum albumin. During a 20-min gamma-camera recording, radioactive degradation products only appeared in the plasma after 10–12 min. Previous administration of a 10 000-fold excess of unlabelled insulin and 5 ml glucose (20%) did not modify the evolution of 131I-labelled insulin cardiac invasion and the subsequent linear decrease of radioactivity. Conversely, wash-out of radioactivity from the liver and kidney was accelerated after preadministration of this excess of unlabelled hormone, binding in these organs accounting for this acceleration. Urinary bladder filling was imaged later than cardiac, hepatic or renal labelling and was only accelerated by polyuria induced by glucose injection, independent of preadministration of unlabelled hormone.
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Oxytocin and bovine neurophysin I (bNpI) were estimated by radioimmunoassay in jugular vein plasma which was collected continuously from 18 bulls. No release of peptides was observed during successive matings with a cow in oestrus or during successive mountings on a cow with ejaculations into an artificial vagina. Stimulation with an electro-ejaculator or, to a smaller extent, massage of the seminal vesicles and ampullae per rectum caused an increase of oxytocin accompanied by a release of bNpI. It is speculated that the release of these peptides is due to stimulation of afferent pelvic nerves in the rectal wall. Basal molar ratios of bNpI/oxytocin in the plasma were highly variable, often showing a large excess of either bNpI or oxytocin. After the onset of peptide release induced by stimulation, molar ratios approached 1:1. This might indicate that hormone release is by exocytosis. Basal bNpI does not provide a good reflection of the oxytocin level.
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Neurohypophysial hormones are thought to be involved in alterations in fluid balance during pregnancy and delivery. In the course of normal pregnancy intravascular volume is increased whereas sodium restriction is thought to reduce plasma volume and cardiac output. In the present study, we measured the effect of long-term severe sodium restriction on vasopressin (AVP) and oxytocin (OT) levels during normal pregnancy and after delivery.
Fifty-nine healthy nulliparous women were randomized either for a low sodium diet (20 mmol sodium daily) or for a normal diet from week 12 of pregnancy onwards. Circulating plasma levels and urinary excretion of AVP and OT, their neurophysins (Np-AVP and Np-OT) and AVP bound to platelets were determined at regular intervals during pregnancy and after delivery. After completion of the study, women on a sodium-restricted diet were compared with control women on a normal diet using repeated measurement ANOVA with adjustment for potentially confounding variables.
After randomization, a reduction in urinary sodium excretion of, on average, 40–82% was found. In general, no effect of sodium restriction could be demonstrated on the various parameters (0·53<P<0·98) with the exception of a significantly lower 24-h urinary AVP excretion by non-smokers with sodium restriction compared with non-smokers having a normal diet (P=0·018) For all parameters, clear changes were found in the course of pregnancy and puerperium (P<0·0001 to P<0·005). Platelet-bound AVP decreased and Np-OT increased during pregnancy. After birth, free plasma AVP, plateletbound AVP, OT, osmolality, sodium and potassium increased, while Np-AVP and Np-OT decreased.
Although elevated Np-AVP and Np-OT levels during pregnancy seem to indicate increased release of neurohypophysial hormones, pregnancy up to 36 weeks of gestation is accompanied by low circulating AVP and OT levels.
Long-term severe sodium restriction diminishes urinary AVP excretion in (non-smoking) pregnant women, without changing circulating levels of AVP and OT, despite the known reduction in circulating volume. The reduced circulating (platelet-bound) AVP levels during pregnancy, whether or not in combination with severe sodium restriction, support the absence of significant non-osmotic stimulation of AVP during pregnancy.
Journal of Endocrinology (1997) 152, 345–354
