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Effect of estradiol-17 beta (E2) and progesterone (P4) on serum arginine vasotocin (AVT) concentration was examined. Serum AVT concentration was lower in nonlaying hens than in laying hens. A single intramuscular injection of E2 or P4 into nonlaying hens caused an increase in serum AVT concentration, suggesting that estrogen and P4 may stimulate the release of AVT from the neurohypophysis.
Arginine vasotocin (AVT), an avian neurohypophysial hormone, is released during osmotic stimulation and oviposition. In the present study, the role of opioid peptides on AVT release was studied by examining the effects of an opioid agonist and antagonist on osmotic- and oviposition-induced secretion of AVT. The administration of hypertonic saline (1.5 M NaCl) induced an increase in the plasma levels of AVT. The simultaneous administration of morphine, an opioid receptor agonist, inhibited the osmotically induced increase in plasma levels of AVT in a dose-dependent manner. On the other hand, the co-administration of morphine with naloxone, an opioid receptor antagonist, attenuated the inhibitory effect of morphine. Moreover, injection of naloxone alone enhanced the osmotically induced increase in plasma levels of AVT. However, the administration of morphine did not inhibit the oviposition-induced increase in plasma levels of AVT. These results suggest that osmotic-induced release of AVT may be under opioid regulation, while oviposition-induced release of AVT may be controlled by a different mechanism. J. Exp. Zool. 286:481-486, 2000.
We developed a radioactive ligand for tumors expressing oxytocin receptors (OTRs) by linking the chelating agent 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid (DOTA) to Lys(8)-vasotocin (LVT), an analogue of oxytocin with high affinity for OTRs. The new reagent (DOTA-LVT) retained high affinity for human OTRs, as proved by in vitro affinity binding to cells endogenously expressing OTRs, such as MCF7 breast carcinoma and MOG-U-V-W glioblastoma cells lines, as well as to transiently transfected COS7 cells. In in vivo experiments, DOTA-LVT carrying (111)In showed specific binding activity to OTR-positive TS/A mouse mammary tumors. The present study opens new perspectives for imaging and, possibly, therapy of OTR-positive human tumors such as breast and endometrial carcinomas, neuroblastomas, and glioblastomas.
The electrical activity of magnocellular neurosecretory cells (NSCs) is correlated with the release rates of neurohypophysial hormones. NSCs may control their secretory activity in a cooperative manner by changing their electrical activity in response to changes in the internal milieu. In the present study, we applied confocal Ca(2+) imaging to a sagittally hemisected rainbow trout brain to simultaneously monitor the neuronal activity of a number of NSCs. We found that NSCs in vitro showed synchronized pulsatile elevations of intracellular Ca(2+) levels at regular intervals. Double immunostaining of vasotocin (VT) and isotocin (IT) after the confocal imaging clarified that each of the VT and IT neuronal populations showed a distinct pattern of periodic Ca(2+) pulses. Simultaneous cell-attached patch recordings ensured that individual Ca(2+) pulses were associated with a phasic burst firing. Depolarizing stimuli by increasing the extracellular K(+) concentration from 5 to 7-9 mm reversibly shortened the interpulse intervals in both VT and IT neurons. Interpulse intervals but not durations of pulses were shortened by hypo-osmotic stimuli and prolonged by hyperosmotic stimuli, consistent with the osmoregulatory function of teleost NSCs. We therefore hypothesize that NSCs use intervals of synchronized periodic burst discharges to fit the levels of secretory activity to physiological requirements.
Covering more than 30 years of studying the pineal peptide hormones physiology, this study largely discusses the main personal research as well as international literature indirectly or directly supporting the idea that the nonapeptide hormone arginine-vasotocin (AVT) is a pineal hormone in mammals. After a short review of the problem, the data are structured in two chapters: one including all the indirect arguments, i.e. those results demonstrating that the ly synthetic exogenous AVT mimics all the effects attributed to the pineal gland itself or to its releasing hormone the indole melatonin, or are contrary to those reported after pinealectomy, and a second chapter that includes all the data directly demonstrating that AVT is contained, synthetized and released from the pineal gland of mammals. Special emphasis was placed on the personal results regarding the AVT effects, the mechanisms of action, the release and interference with some of the basic functions of the brain such as sleep, behaviour, attention or maturation.
1. The threshold level of exogenous arginine vasotocin (AVT) for increasing the cutaneous water permeability in Bufo bufo was several times higher than has been measured in dehydrated frogs and toads. 2. The beta-agonist isoproterenol was without effect on water balance in hydrated toads but increased the response to large doses of AVT by 25-50%. 3. Implantation of cortisol pellets in water-acclimated toads enhanced the cutaneous water permeability by a factor of 2-3. 4. It is concluded that understanding of water balance in terrestrial anurans may depend upon the unravelling of mechanisms that integrate cutaneous water transport and diuresis.
We have cloned and determined the nucleotide sequences of cDNAs encoding precursors of neurohypophysial hormones, vasotocin (VT) and isotocin (IT), from the hypothalamus of masu salmon, Oncorhynchus masou. The deduced amino acid sequences of masu salmon VT and IT precursors (proVT-I and proIT-I) are highly homologous to those of chum salmon proVT-I and proIT-I, respectively. The VT and IT precursors are composed of a signal peptide, hormone and neurophysin (NP), the middle portion of which is highly conserved among vertebrates. Both the NPs extend about 30 amino acids at the C-terminal. The extended C-terminals have a leucin-rich segment in the carboxyl-terminal, as copeptin of vasopressin precursor. Southern bot analysis showed the presence of two types of proVT genes (proVT-I and proVT-II) and proIT genes (proIT-I and proIT-II) in an individual masu salmon, as in a chum salmon. Southern blot analysis with proVT probes further suggested that at least two different types of proVT-I genes exist in a single masu salmon. Northern blot analysis indicated that proVT-I and proIT-I genes are expressed in the hypothalamus, whereas proVT-II and proIT-II genes are not expressed. Evolutionary distance between proVT-I and proIT-I genes was statistically estimated based on synonymous nucleotide substitution in the coding region of the cDNAs. The magnitude of distance between masu salmon proVT-I and proIT-I genes suggested that the highly conserved central portion of NPs resulted from a gene conversion event. Between masu salmon and chum salmon, evolutionary distance for proVT-I genes is about 6-fold larger than that for proIT-I genes.
Extrasynaptic effects of vasopressin, oxytocin, vasotocin on the membrane electrosensitive ionic channels were studied in model experiments using isolated somata from the CNS of mollusc Lymnaea stagnalis. The neuropeptide in concentrations of 1.10(-16)-1.10(-6) mol/l either blocked or induced biphasic dose-dependent effect on amplitudes of the membrane ionic currents.
By means of the peroxidase-antiperoxidase technique a comparative immunocytochemical study of the distribution of the vasotocin- and vasopressin-reacting system in the chicken and rat hypothalamus was carried out. In both species it is possible to distinguish, on the basis of their topographical location, three different comparable populations: The first one is situated very close to the pial surface and the optic chiasma (L1 and L2 groups in the chicken and the supraoptic nucleus in the rat). The second one is located near to the third ventricle and corresponds to the suprachiasmatic nucleus of both species and the periventricular groups of the chicken (P1, P2, and P3 groups) and the periventricular subdivision of the paraventricular nucleus of the rat. The third one is situated between the two previous populations and consists of small clusters of reacting neurons (L3 and L5 groups in the chicken and the nucleus circularis and fornicalis in the rat) and to a large cluster of reacting neurons (L4 group in the chicken and the magnocellular part of the paraventricular nucleus in rat). In the median eminence of the chicken the immunoreactive axons were located in the internal zone and the anterior part of the external zone. However in the rat, the reaction was exclusively located in the internal zone.
Using morphometric technique, it has been shown that single and especially three successive injections of a hypothalamic nonapeptide neurohormone, arginin-vasotocin (5.10(-9) M/kg of body weight) affect functional activity of the thyroid gland in sexually mature male frogs which had been subjected to hypophysectomy 10 or 60 days before neurohormonal treatment. These data presumably confirm a hypothesis about the direct para-adenohypophysial influence of the hypothalamic nonapeptide neurohormone on the peripheral endocrine glands, particularly, the thyroid one.
The pineal nonapeptide hormone arginine vasotocin (AVT) is synthesized by the ependymal cells of the pineal recess and subcommissural organ and stored in so far undefined cells of the pineal gland proper. AVT is first released into the cerebrospinal fluid (CSF) and reaches the blood only secondarily after its absorption from CSF. It displays a diurnal rhythm in the pineal and CSF, suggesting its release into the CSF during the night in the dark. Melatonin represents its releasing hormone. AVT exerts both its endocrine and non-endocrine effects by a unique mechanism involving the activation of serotonin neurotransmission in the brain with resultant inhibition of release of hypothalamic releasing and inhibiting hormones and induction of sleep. It produces both its endocrine effects and sleep at concentrations equivalent to only several hundreds of molecules, being thus by far the most active hormone so far known. Midbrain raphe nuclei or some structures intimately correlated with these cell bodies, most contain the extremely sensitive and specific AVT receptors in the mammalian brain. In contrast with its natural analogues arginine vasopressin and oxytocin which are mainly blood hormones, AVT is a CSF hormone whose major if not the sole site of action is the brain itself.
Arginine vasotocin (AVT) or placebo were subcutaneously administered to 4 men at 22.00 and 01.00 h, along four nights, and polygraphic recordings were performed between 22.00 and 02.00 h during sleep. AVT significantly increased only the amount of rapid eye movement (REM) sleep (p less than 0.05), but did not influence the latency of the first REM sleep period. This effect of AVT was not dose dependent in the range between 2 and 12 microgram AVT. AVT or placebo were also intravenously injected or perfused to 10 normal adult subjects, at different times of the day, under clinical control. Doses between 2 microgram perfused 4 h and 12 microgram perfused 30 min, did not produce clinical signs of sleep. It is suggested that AVT is not a blood factor for inducing of slow waves sleep (SWS) or REM sleep in humans.
The lumbar cerebrospinal fluid (CSF) collected from 6 narcoleptic patients (three males and three females) aged between 31 and 47 years, as well as from 2 patients having Pickwickian syndromes with hypersomnia attacks (two males), aged 43-51 years, contained relatively high amounts of arginine vasotocin (AVT) only if the CSF was removed after a REM sleep period. The release was not induced by darkness since the same release of AVT occurred when the CSF was removed after a REM sleep period during daylight hours. No detectable AVT levels have been found in the CSF samples of four narcoleptics collected after a NREM period of sleep, either during night or daylight hours. The present results suggest a possible alteration of the rhythmical release of AVT both in narcolepsy and in narcoleptic syndromes.
Lumbar cerebrospinal fluid (CSF) of seven healthy male volunteers contains detectable levels of arginine vasotocin (AVT) when CSF was removed after awakening from rapid eye movement (REM) sleep. No detectable levels of AVT were found in the CSF of the same subjects when CSF WAS removed after awakening from non rapid eye movement (NREM) sleep. The amount of AVT detected in CSF after REM sleep was significantly higher if the subjects experienced vivid and emotive dreams. The present results provide the first evidence for a REM sleep dependent release of AVT into CSF of man.
The interrelationship between prostaglandins (PG) and vasotocin (AVT) in the oviposition of the domestic hen was investigated. Single or combined injections of indomethacin (IND), an inhibitor of PG synthesis, and AVT gave delay or induction of oviposition. Injection (i.m.) of IND (5 mg/kg) 5 h before oviposition resulted in 15.1 h (+/- 0.93) delay of oviposition. Injection (i.v.) of AVT (0.1 microgram/kg) 2.5 h before oviposition caused premature oviposition within a few minutes (3.1 +/- 0.2). Combined injection of IND and AVT at 5 h and 2.5 h, respectively, before oviposition caused the delay of oviposition (15.8 h +/- 0.8). The results indicate that IND blocked the induction of oviposition by AVT.
The antidiuretic activity of an arginine vasotocin (AVT) solution (10 microU/ml) was studied in comparison with an arginine vasopressin (AVP) solution (10 microU/ml) after their incubation for 1 h at 37 degrees C with the supernatants (S) or the pellets (P) of the habenular nuclei (HN) or frontal cortex (FC) fragments homogenized in saline solution, removed from adult or newborn rats. Both SHN and SFC from adults inactivated about 5 microU/ml AVT and 10 microU/ml AVP, PHN and not PFC inactivated only about 7 microU/ml. In newborns the phenomena were in the same direction, but the specific inactivation of AVT by the PHN was of about twice greater than in adults. The results are interpreted as suggesting that, in contrast to an unspecific inactivation from S, probably of an enzymatic nature, the PHN specifically bind AVT and that this activity is greater in newborn than in adult rats.
Standard electroencephalographic (EEG) anomalies were correlated with the intensity of the acute intranasally administered arginine vasotocin (AVT) effects on the REM sleep of 27 healthy prepubertal children (aged between 4 and 13 years). In comparison with saline controls, AVT greatly enhanced REM sleep parameters in subjects with alpha rhythm anomalies, theta waves or with low-voltage EEG as well as in those without hyperpnea-induced EEG anomalies, than in those without (and respectively with) these anomalies. No statistical significant correlation could be established between the intensity of AVT effects on sleep and age, sex, appearance of incidental delta waves or of paroxysmal activities. It is concluded that standard EEG might predict the intensity of the hypnogenic effects of AVT in prepubertal children. The present results support the hypothesis that AVT could be involved in the maturation of the electrical activity of the brain.
In order to investigate a possible involvement of the GABA-ergic neurotransmission in the effects of arginine vasotocin (AVT) hormone on human sleep, we administered in 20 healthy prepubertal boys (aged 7-12 years), by an intra-nasal route, AVT (1 microgram) alone or 10 minutes after an intra-nasal dose of valproic acid (VA) (1, 10 and 50 micrograms). Whether the dose of 50 micrograms VA alone produced a quasi-total insomnia for all recording time (3h), the doses of 1 and 10 micrograms VA were without any apparent effect on sleep parameters. However, whatever be the dose of VA, it produced a total suppression of the hypnogenic effects of AVT. The results suggest not only a possible involvement of the GABA-ergic mechanisms in mediating the hypnogenic properties of AVT in man, but also that VA could be used in the treatment of excessive sleep syndromes, especially of narcolepsy.