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SUMMARY
The coated charcoal immunoassay method was applied to the measurement of the corticotrophin (ACTH) response to insulin hypoglycaemia, lysine-vasopressin, metyrapone and surgical stress in female piglets. The maximum ACTH responses average 392 picograms (pg.)/ml. (insulin hypoglycaemia), 111 pg./ml. (lysine-vasopressin) and exceeded 350 pg./ml. after metyrapone. The time relationships between blood sugar, 11-hydroxycorticosteroid and ACTH levels were also examined. Despite constant infusion rates, the ACTH response to lysine-vasopressin was not sustained. Previous administration of dexamethasone suppressed the response to insulin hypoglycaemia and lysine-vasopressin.
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SUMMARY
1. Rat kidney slices inactivated 8-arginine vasopressin 1·23 times as fast as 8-lysine vasopressin and 2·14 times as fast as 2-phenylalanine-8-lysine vasopressin. The rate of inactivation became dependent upon the initial concentration of these peptides when this reached 8–11 μg./ml. There was a positive correlation between the apparent first-order rate constants of these vasopressins and their pressor potency per mg. peptide.
2. 8-Arginine vasopressin was not inactivated by hyaluronidase but rat kidney slices inactivated 8-arginine vasopressin 1·25 times as fast when testicular hyaluronidase was present.
3. Slices of rat kidney taken 7 days after bilateral adrenalectomy inactivated 8-arginine vasopressin at the same rate as those taken from normal animals. Cortisol sodium succinate did not affect the rate of 8-arginine vasopressin inactivation by normal rat kidney slices, but there was no increased rate of inactivation when hyaluronidase, 8-arginine vasopressin and cortisol sodium succinate were incubated together with normal rat kidney slices.
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nucleus is comprised of two major neurosecretory components – the mPVN and pPVN subdivisions. Neurones originating from the more medially situated pPVN (where vasopressin (AVP) is co-localised in a proportion of corticotrophin-releasing factor (CRF
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ABSTRACT
Vasopressin (VP)-like immunoreactivity (IR) has been located in the testes of several species of mammal. There is evidence that most of this IR in the rat does not represent authentic arginine vasopressin (AVP) and that a second AVP-like peptide may exist. We have studied testis samples from the pig, which produces lysine vasopressin (LVP) in its pituitary, and have found both LVP- and AVP-like IR.
High-performance liquid chromatography (HPLC) of testis extracts showed two peaks of VP-IR. The first peak co-eluted with authentic LVP and was recognized only by antisera which cross-reacted with LVP. The second peak co-eluted with authentic AVP and was recognized by antisera raised against AVP. Both VP-like peptides bound to a neurophysin affinity column and the HPLC elution profiles of the bound peptides were similar to those of the authentic hormones. When the LVP-like material was oxidized with performic acid, a peak of IR running in the same position as oxidized authentic LVP on HPLC was produced. Similarly, the performic acid-oxidized AVP-like material co-eluted with oxidized authentic AVP.
The presence of both LVP- and AVP-like peptides in the pig testis may mean that more than one gene is involved. A second VP-like gene could also explain the anomalies of VP-IR in other species.
J. Endocr. (1988) 117, 441–446
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Stewart (1971) showed that mice of the Peru strain produce [8-lysine]-vasopressin rather than [8-arginine]-vasopressin which is found in other strains of mice and is the usual form of the neurohypophysial hormone in mammals other than the Suina (Ferguson & Heller, 1965). Most mammals are more sensitive to [8-arginine]-vasopressin than [8-lysine]-vasopressin as an antidiuretic hormone (Sawyer, Chan & van Dyke, 1962); but in pigs [8-lysine]-vasopressin is nearly as potent as [8-arginine]-vasopressin (Ferguson & Heller, 1965), indicating some co-adaptation of the renal receptors and the chemical structure of the hormone. It was therefore decided to assess the relative sensitivity of Peru and CBA/FaCam mice to [8-arginine]-vasopressin and [8-lysine]-vasopressin.
Although stomach-loading of conscious Peru mice will induce a rapid water diuresis (Stewart, 1968), this is inhibited by anaesthesia and operational stress. Two bioassay methods using conscious animals have therefore been developed and used on CBA/FaCam and Peru adult male mice. In one method,
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SUMMARY
Hypercalcaemia produced in rats by the intravenous injection of calcium chloride, slowed the rate of disappearance of injected vasopressin from the blood circulation. 24% of the vasopressin injected appeared in the urine of hypercalcaemic rats compared with 7 % in control animals.
Vasopressin injected intravenously into control rats was distributed in a volume equal to the blood volume but when rats had been made hypercalcaemic, the theoretical volume of distribution was three to four times greater. Antidiuresis produced by injection of large doses of vasopressin into hydrated rats was little affected by changes in the blood concentration of calcium. Calcium chloride injected intravenously into hydrated rats resulted in a temporary antidiuresis.
Experiments in vitro with Sephadex G-25 showed that both ox neurophysin and rat serum protein bind vasopressin and that calcium interferes with the binding.
It is suggested that calcium can compete directly with vasopressin for acidic binding sites on proteins; that this can cause the release of vasopressin and alter the transport and possibly the rate of inactivation, of vasopressin.
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1. A method has been described for the assay of vasopressin by intravenous injection in unanaesthetized rats.
2. The choice of parameters for the expression of antidiuretic responses has been studied in rats and rabbits.
3. It has been shown that the sensitivity of rats to injected vasopressin is independent of the water load within the range of 6–9% of the body weight.
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Division of Pharmacology and Therapeutics, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada T2N 1N4
(Received 26 February 1976)
The production of highly specific antisera to oxytocin and vasopressin for radioimmunoassay was only recently achieved (Chard, 1973). Two major difficulties encountered in the attempts at production of antisera to these hormones have been: first, that both hormones have low molecular weights (approximately 1000); and secondly, they are usually native to the animals being immunized, although [Arg8]-vasopressin (AVP) has been successfully used for the production of antisera in rabbits. The molecular weights can be augmented by covalently coupling the hormones, before immunization, to large molecular weight ligands such as thyroglobulin (Skowsky & Fisher, 1972; Chard, 1973). [8-Lysine]-vasopressin (LVP), which is found in suiformes, is closely related chemically and biologically to AVP - the vasopressin of most mammals. Lysine-vasopressin has been used successfully for the production of antisera for radioimmunoassays (Skowsky,
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SUMMARY
The effects of vasopressin analogues with selective antidiuretic activity have been tested on the isolated toad bladder.
Analogues of oxytocin and 8-Arg vasopressin lacking the terminal amino group had reduced effects on water (hydro-osmotic effect) and sodium (natriferic effect) transfer across the bladder. The natriferic effect of deamino-8-Arg vasopressin was reduced 3·5 times more than its hydro-osmotic effect.
Deamino-2-Phe, 8-Arg vasopressin had a reduced hydro-osmotic action compared with deamino-8-Arg vasopressin (6 times less) while the reduction of the natriferic effect was far more pronounced (68 times).
The selective antidiuretic, compared to pressor, potency of these analogues is discussed in relation to their selective hydro-osmotic compared to natriferic potency.
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SUMMARY
The pituitary glands of 11 rats (six females and five males, weighing 140–200g.) with hereditary hypothalamic diabetes insipidus (DI) were found to contain oxytocin but no vasopressin.
The DI rats could not always be distinguished from rats without diabetes insipidus (non-diabetes insipidus, NDI rats) by measurement of their daily urine volume.
Stimulation of the neurohypophysis by fall in arterial pressure (haemorrhage, methacholine) or by nicotine, released vasopressin in NDI rats to produce a sustained antidiuresis, but in the DI rats there was only a transient fall in urine flow which did not outlast the hypotension.
The DI rats were about twice as sensitive to vasopressin as NDI rats. As assay preparations they have the advantage that they cannot respond to vasopressin-releasing stimuli.
Prolonged administration of Pitressin tannate in oil increased maximum urinary osmolality in DI rats, but failed to increase their sensitivity to intravenously injected vasopressin.
