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Transversal and longitudinal aortic bulb strips show isometric contractions in response to the vasotocin action. The extreme sensitivity of the preparations correspond to a final hormone concentration of 8.25 X 10(-16) M.
The effect of naredrenaline and acetylcholine on the blood arginine vasotocin (AVT) level in hens as well as the effect of reserpine and atropine on the release of this hormone following the intravenous injection of hypertonic NaCl solution were investigated. It was dound that noradrenaline causes a decrease in blood AVT level in contrast to acetylcholine. Reserpine itself caused a rise in the blood AVT level; the effect was also found after administration of hypertonic solution. Atropine had no effect on the blood AVT level, but inhibited the AVT release following the adminstration of hypertonic Nacl solution.
Arginine vasotocin (AVT), a neuropeptide, appears to influence mating and aggressive behaviours of males classically thought to be controlled by testosterone. We examined the effects of AVT on the calling behaviour and competitive ability of the grey treefrog Hyla versicolor under natural field conditions. AVT increased the probability that males produced advertisement calls from a resident's calling site. Most intriguing, AVT increased an intruder male's ability to acquire calling sites from resident males without physical aggression in staged encounters. This is particularly significant because resident males typically win encounters over intruders. This is the first study demonstrating that AVT manipulations in a natural population can directly influence the outcome of male-male competition for a resource and reverse the resident-male advantage. Copyright 1998 The Association for the Study of Animal Behaviour.
We investigated the effects of different doses (0, 2.5, 25 and 250 µg) of the neuropeptide arginine vasotocin (AVT) on the calling characteristics of the grey treefrog in a chorus in its natural habitat. AVT changed some call characteristics known to influence social behaviour in grey treefrogs. It increased call duration and number of pulses in a call, but not dominant frequency, call rate or pulse effort. Saline injections and handling did not produce significant changes in any of the call characteristics. In addition, individual animals injected with AVT only rarely produced call characteristics that were outside of the range found in the preinjection measurements, suggesting that AVT does not cause abnormal calling behaviour. Other researchers have demonstrated that longer calls with more pulses are produced by males when chorus densities increase, and females display a strong preference for longer calls with more pulses. This suggests that the changes induced by AVT injections may have functional consequences in social interactions. We previously demonstrated that AVT-injected males (25 µg AVT) displaced resident males from calling sites through changes in calling behaviour under natural field conditions. Our results indicate that changes in call duration and pulse number could contribute to the unmanipulated resident male's behaviour towards the AVT-injected intruder, perhaps because the calls are more attractive to females or because the calls are perceived as more aggressive. Copyright 2000 The Association for the Study of Animal Behaviour.
Recent morphological, physiological, and molecular studies that shed light on the functional significance of the neurohypophysial peptide arginine vasotocin (AVT) in the reptilian kidney are reviewed. Several structural features of the reptilian nephron are highlighted, including the presence of an incipient juxta-glomerular apparatus, aglomerular nephrons, and the thin, very short intermediate segment (IS) joining proximal and distal convoluted tubules. Although the V(2)-like AVT receptor and its gene have yet to be sequenced in any reptile, AVT receptors have been located in both the IS and the branched collecting duct system in the agamid lizard Ctenophorus ornatus. These findings suggest that AVT may have a dual effect in the reptilian kidney, first diluting the urinary fluid in the thin-intermediate segment, prior to its entering the collecting duct system, and then facilitating water reabsorption along an osmotic gradient as the urine passes through the final segments of the nephron. The IS may thus prove to be the evolutionary homologue of the thin-ascending limb of the loop of Henle in the mammalian kidney.
Although the neuropeptide arginine vasotocin (AVT) is found in several auditory and vocalization regions of the bullfrog (Rana catesbeiana) brain, its functions in these areas are unknown. We examined the effects of AVT injection on two auditory-evoked reproductive behaviors: advertisement calling in male bullfrogs and call phonotaxis in female bullfrogs. AVT (500 micrograms; intraperitoneal) significantly increased advertisement call frequency and decreased calling latency in male bullfrogs, compared to saline injection. This dose of AVT also significantly decreased the time required for female bullfrogs to reach a call source as well as the latency of females to leave the starting position during call playback. In both males and females, these effects were significant at 0.5 hr and persisted until at least 2 hr after injection. AVT thus facilitated display of two sexually-dimorphic reproductive behaviors in bullfrogs. These effects may be due to direct effects of AVT on auditory processing regions in the bullfrog brain.
A microassay was developed to measure the binding of the labelled monoiodinated analogue [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid), 2-O-methyltyrosine, 4-threonine, 8-ornithine, 9-125I-tyrosylamide]vasotocin [125I-d(CH2)5[Tyr (Me)2, Thr4, Tyr-NH(2)9]OVT] to isolated nephron segments microdissected from collagenase-treated rat kidneys. When determined using 1.7 nM labelled ligand at 4 degrees C, specific binding sites (expressed at 10(-18) mol 125I-d(CH2)5[Tyr (Me)2, Thr4, Tyr-NH(2)9]OVT bound/mm tubule length) were found in medullary thick ascending limbs (MTAL), 1.67 +/- 0.49; cortical thick ascending limbs, 2.20 +/- 0.80; cortical collecting ducts, 2.39 +/- 0.86; outer medullary collecting ducts (OMCD), 2.54 +/- 0.53 and inner medullary collecting ducts, 5.33 +/- 0.40, whereas no specific binding could be detected in glomeruli and proximal tubules. Specific 125I-d(CH2)5[Tyr (Me)2, Thr4, Tyr-NH(2)9]OVT binding to OMCD was saturable with incubation time and reversible after elimination of free labelled ligand (the association and dissociation rate constants at 4 degrees C were 1.06 x 10(7) M-1 min-1 and 1.95 x 10(-2) min-1 respectively). The stereospecificity of MTAL and OMCD binding sites was assessed in competitive experiments revealing the following recognition pattern for a series of eight vasopressin analogues:dDAVP greater than AVP greater than d(CH2)5-[Tyr (Me)2, Thr4, Tyr-NH(2)9]OVT = AVT = OT greater than d(CH2)5[Tyr(Me)2]AVP = [Thr4, Gly7]OT greater than [Phe2, Orn8]VT, whereas pharmacological concentrations of insulin and glucagon did not impair radioligand binding. These results indicate that the detected labelled binding sites might correspond mainly to physiological V2 vasopressin receptors.
Arginine-vasotocine (AVT) injected into male adult lizards, Podarcis s. sicula Raf., inhibits the last phases of spermatogenesis and the endocrine activity of gonads. In female lizards the substance induces an early interruption of egg deposition.
Radioimmunoassays and high pressure liquid chromatography have been used to demonstrate the presence of an arginine-vasotocin-like peptide (AVT) in the anterior ganglia of Aplysia. Previously, AVT, using similar methods, was found to be present only in vertebrates. AVT when perfused over the abdominal ganglion (10(-6)-10(-12)M) was found to increase the bursting activity of R15, to decrease the bursting activity of L3-L6 and to increase the CNS's suppressive influence over the gill withdrawal reflex evoked by siphon stimulation. The AVT present in the nervous system of Aplysia may mediate long-term suppression of gill reflex behaviors induced by factors such as satiation and, as well, regulate the activity of certain neurosecretory neurons.
Putative receptors for arginine vasotocin (AVT) in the brain of the newt (Taricha granulosa) were measured using quantitative autoradiography with tritium-labelled vasopressin. Specific binding sites were observed in the olfactory bulb, medial (hippocampal) pallium, dorsal pallium, amygdala para lateralis and tegmental region of the medulla oblongata. In both male and female newts, concentrations of binding sites in the amygdala, but not in the other four areas, were significantly lower in gonadectomized animals than in sham-operated controls. The equilibrium dissociation constants (KdS) were not altered by gonadectomy. Since long-tem castration abolishes the effect of AVT injection on sexual behaviors, these results support the hypothesis that gonadal steroids maintain sexual behaviors in this amphibian by maintaining AVT receptors in the amygdala.
The effect of an intracerebroventricular (i.c.v.) injection of the oxytocin antagonist, d(CH2)5Tyr(Me)-Orn8-vasotocin, on the copulatory behaviour of vigorous male rats in the presence of females in estrus was studied. The peptide (2.5, 25 and 50 ng, 15 min before mating tests) decreased the number of mounts and intromissions, and abolished ejaculation almost completely at all doses tested. The peptide failed to significantly influence motor activity at the doses used. The results support the hypothesis that central oxytocin plays a physiological role in the expression of copulatory behaviour.
The distribution and characteristics of putative arginine vasotocin (AVT) receptors in the urodele amphibian kidney were investigated using in vitro quantitative autoradiography. Specific binding sites for [3H]arginine vasopressin (AVP) in the kidney of the rough-skinned newt (Taricha granulosa) were located over the glomeruli. Scatchard analysis showed that, in the range of concentrations tested (0.2 to 22 nM), [3H]AVP bound to a single class of receptors with a dissociation constant of 1.4 nM and a binding site concentration of 36.5 fmol/mg protein. Binding displacement studies showed that both AVT and AVP were potent ligands for newt kidney receptors. Two specific antagonist peptides with anti-vasopressor (V1) activity, but not anti-antidiuretic (V2) activity, in rat tissues were tested as well. Both antagonists effectively displaced [3H]AVP from receptor sites in newt kidney slices, indicating that the binding sites in this amphibian resemble the V1 subtype of mammals in ligand specificity. Localization of AVT receptors over kidney glomeruli and ligand specificity of these sites is consistent with the hypothesis that AVT may cause antidiuresis in urodele amphibians at least in part via a glomerular vasoconstricting action.
The effect of the intracerebroventricular (ICV) injection of the oxytocin antagonist d(CH2)5Tyr(Me)-Orn8-vasotocin on the stimulation of copulatory behavior induced by the dopamine (DA) agonist apomorphine was studied in male rats. Apomorphine (80 micrograms/kg SC) given 5 min before mating tests decreased intromission frequency and ejaculation latency in experienced male rats. Such effects were abolished and reversed by pretreatment with 50 and 1000 ng of the oxytocin antagonist given ICV 5 min before apomorphine. The peptide per se markedly increased intromission and ejaculation latency and abolished ejaculation in control rats. The results suggest that brain oxytocin is implicated in the expression of sexual behavior, and apomorphine might improve male copulatory behavior by releasing oxytocin in brain.
The effect of the prostaglandin blocker indomethacin on arginine vasotocin-induced birth was examined. Gravid female, oviparous (Sceloporus undulatus ) and viviparous (Sceloporus jarrovi ) lizards were pretreated with saline or indomethacin, a potent blocker of PG synthesis. Pretreatment was followed by an intraperitoneal injection of AVT. Pretreatment with indomethacin significantly delayed the onset of AVT-induced oviposition in S. undulatus , whereas it had no effect on latency to birth in S. jarrovi . Female S. jarrovi treated with indomethacin, however, gave birth to only part of the total litter, whereas control females gave birth to complete litters. In viviparous females, an interaction of embryonic age with pretreatment was evident; females having more developed embryos decreased birth latency significantly and increased the percentage of parturition when compared with females that had embryos at earlier stages of development. Our data suggest that although exogenous AVT can stimulate oviposition or parturition, these events occur more rapidly and completely when prostaglandin synthesis is not inhibited.
The effects of microiontophoretically applied oxytocin on the firing rates of neurones in the rat caudal brainstem have been examined. Of the sample of 156 units recorded the firing rates of 33.3% were reduced and those of 21.2% were raised by microiontophoretically applied oxytocin, whilst the remainder were unaffected. The distribution of units facilitated by oxytocin tended to overlap with the distribution of oxytocin demonstrated immunocytochemically, whereas many units inhibited by oxytocin were in regions where no oxytocin was observed. Overall the excitatory but not the inhibitory effects of oxytocin could be blocked by oxytocin and vasotocin analogues with antagonist properties.
Extremely small amounts (10(-4) pg) of the pineal nonapeptide arginine vasotocin (AVT), injected into the pineal recess of freely moving cats, decreased the levels of 5-hydroxyindole acetic acid (5-HIAA) in the raphe dorsalis nucleus and induced slow wave sleep. In cats with lesions in the lateral habenula, 10(-4) pg AVT injected into the pineal recess, failed to decrease raphe dorsalis 5-HIAA levels and to induce slow wave sleep. The GABA antagonist picrotoxin (1 ng) injected into the pineal recess 15 min before the administration of AVT (10(-4) pg), completely prevented AVT from decreasing raphe dorsalis 5-HIAA levels and from inducing slow wave sleep. A highly significant correlation could be established between the decrease of raphe dorsalis 5-HIAA levels and the induction of slow wave sleep. No changes in raphe dorsalis 5-HIAA levels could be detected in cats injected with 10(-4) pg AVT into the lateral or into the fourth ventricle. Neither arginine vasopressin nor oxytocin (10(-4) pg) injected into the pineal recess, could alter raphe dorsalis 5-HIAA levels. It is concluded that AVT induces slow-wave sleep in cats by activating an inhibitory GABAergic lateral habenula-raphe dorsalis pathway.
1. The cardiac effects of arginine vasotocin (AVT) on isolated atria were examined in three anuran and one urodele species. 2. AVT produced dose-related positive chronotropic and inotropic responses. 3. The responsiveness of the atrial tissue varied among species. 4. Both the basal atrial rate (AR) and tension (T) were attenuated in the presence of phentolamine and propranolol, alpha- and beta-adrenergic antagonists. Isoproterenol, a beta-adrenergic agonist, increased both AR and T, an effect which would be inhibited by propranolol. 5. The effects of AVT on both AR and T were not inhibited by alpha- and beta-adrenergic blockers, nor by verapamil and imidazole with the dosages used in the present study. 6. On the contrary, the effects of AVT on AR, but not T, was enhanced in the presence of both alpha- and beta-adrenergic blockers. 7. The mechanism of action of AVT on the amphibian atrium remains unknown.
The neurohypophysial hormone arginine vasotocin (AVT) stimulates adrenocorticotropin hormone (ACTH) secretion from the avian anterior pituitary gland resulting in increased adrenal secretion of corticosterone in response to stress. Here, we report molecular cloning and functional characterization of a gene encoding an AVT receptor subtype, designated the VT2 receptor, that may mediate the stimulatory effect of AVT on ACTH secretion in birds. The open reading frame predicts a 425 amino acid polypeptide that includes seven segments of 19 to 24 hydrophobic amino acids, typical of guanine nucleotide-protein coupled receptors. Phylogenetic analysis revealed that the VT2 receptor shares highest identity with the mammalian V1b-vasopressin receptor subtype. Expressed VT2 receptors in COS7 cells mediate AVT-induced phosphatidylinositol turnover and Ca(2+) mobilization. In the domestic chicken, expression of VT2 receptor gene transcripts is limited to the pituitary gland. Based on similarities in sequence, site of expression and coupled signal transduction pathways, we conclude that the VT2 receptor is the avian homolog of the mammalian V1b-vasopressin receptor, and therefore may play an important role in the avian stress response.