Failure to kindle seizures after repeated intracerebral administration of arginine vasopressin

In an attempt to kindle seizures with arginine-vasopressin (AVP), we injected AVP into the amygdala or hippocampus of rats. Although behavioral and electrographic alterations were sometimes observed, seizures failed to develop, even in rats that had previously been kindled with electrical stimulation. This and previous failures to kindle seizures by intraventricular injections of AVP call into question the possibility of AVP kindling.     

Neurohypophyseal hormones protect against pentylenetetrazole-induced seizures in zebrafish: Role of oxytocin-like and V1a-like receptor

Oxytocin (OT) and arginine-vasopressin (AVP) are involved in the physiological response to different stressors like the occurrence of seizures which is regarded as a severe stress factor. Zebrafish (Danio rerio) is recently featured as a model of epilepsy but the role of neurohypophyseal hormones on this teleost is still unknown. We attempted to determine whether non-mammalian homologues like isotocin (IT) and vasotocin (AVT) affected pentylenetetrazole (PTZ)-induced seizures in adult zebrafish in comparison with OT/AVP. The mechanism was studied using the most selective OT and AVP receptor antagonists. Zebrafish were injected i.m. with increasing doses (0.1-40ng/kg) of the neuropeptides 10min before PTZ exposure. DesGly-NH2-d(CH2)5-[D-Tyr2,Thr4]OVT (desglyDTyrOVT) for OT receptor and SR49059 for V1a subtype receptor, were injected together with each agonist 20min before PTZ exposure. All the peptides significantly decreased the number of seizures, increased the mean latency time to the first seizure and decreased lethality. This protective effect led to a dose-response curve following a U-shaped form. IT was approximately 40 times more active than OT while AVT was 20 times more potent than AVP in reducing the number of seizures. DesglyDTyrOVT was more effective in antagonizing OT/IT, while SR49059 mainly blocked AVP/AVT-induced protection against PTZ-induced seizures. The present findings provide direct evidence of an important involvement of IT/OT and AVP/AVT as anticonvulsant agents against PTZ-induced seizures with a receptor-mediated mechanism in zebrafish. These data reinforce zebrafish as an emerging experimental model to study and identify new antiepileptic drugs.     

Thermoregulatory, behavioral and seizure modulatory effects of AVP in the gerbil

Recent reports suggest that arginine vasopressin (AVP) may be an endogenous antipyretic peptide and a mediator of febrile convulsions [10,12]. The spontaneously seizing Mongolian gerbil was used to investigate the thermoregulatory, behavioral and seizure modulatory effects of AVP. Injection of AVP (1.0 and 5.0 μg IV and 0.01–1.0 mg/kg SC) caused dose-related falls in body temperature. Stereotypic scratching, terminated by a body shake, was observed after AVP (1.0–5.0 μg IV). However, such behavior was not observed after subcutaneous injection of AVP. AVP did not potentiate seizure induction in the gerbils but rather reduced the seizure incidence. The data demonstrate that AVP can reduce body temperature and cause specific behaviors, but it does not appear to play a role in the pathogenesis of seizures in the seizure sensitive strain of Mongolian gerbil.     

Metabolism and synthesis of arginine vasopressin in conscious newborn sheep

Arginine vasopressin (AVP) is an important regulator of cardiovascular homeostasis in the fetus, but its role after birth is unclear. Although infused AVP increases mean arterial pressure (MAP) during the 1st mo after birth, pressor responses are unchanged, suggesting that vascular responsiveness is also unchanged. Alternatively, this could reflect increases in AVP metabolic clearance rate (MCR(AVP)). However, newborn AVP metabolism and synthesis are poorly studied. Therefore, we examined the pressor responses to infused AVP and the pattern of circulating AVP, AVP production rate (PR(AVP)), and MCR(AVP) in conscious newborn sheep (n = 5) at 9-38 days after birth. Basal MAP rose and heart rate (HR) fell during the study period (P < or = 0.02), while circulating AVP was unchanged (P > 0.1), averaging 3.01 +/- 0.86 pg/ml. Infused AVP elicited steady-state responses at 10-40 min, increasing plasma AVP and MAP and decreasing HR (P < 0.001). Although pressor responses were unchanged between 9 and 38 days, the rise in MAP correlated with increases in plasma AVP (R = 0.47, P = 0.02, n = 24). MCR(AVP) was unchanged throughout the 1st mo (P > 0.2), averaging 205 +/- 17 ml.kg(-1).min(-1), and was associated with an elevated PR(AVP), 973 +/- 267 pg.kg(-1).min(-1), which also was unchanged (P > 0.1). After birth, MCR(AVP) and PR(AVP) are elevated, probably accounting for the stable plasma AVP levels. The former is also likely to account for the stable pressor responses to infused AVP during the 1st mo. The reason for the elevated PR(AVP) is unclear but may relate to increases in vascular volume associated with postnatal growth.     

Arginine vasopressin as a central neurotransmitter

Anatomical and electrophysiological studies have revealed a widespread innervation of the brain by arginine vasopressin (AVP)-containing fibers. There is evidence that these central AVP pathways may be activated simultaneously with endocrine pathways. Stimulation of hypothalamic nuclei that contain AVP cell bodies causes changes in electrical activity of neurons in areas receiving AVP projections; in these same regions, release of immunoreactive AVP can be detected in response to appropriate stimuli or hypothalamic stimulation. These parts of the brain have also been shown to contain AVP receptors, and application of AVP to cells in these areas alters spontaneous activity or modifies the responses to other transmitters. AVP appears to act as a neurotransmitter involved in the central control of the cardiovascular, renal, and thermoregulatory systems. AVP may act centrally to coordinate autonomic and endocrine responses to homeostatic perturbations.     

Central vasopressin in the modulation of catecholamine release in conscious rats

Neurons containing arginine vasopressin (AVP) have been shown to project from the paraventricular nucleus of the hypothalamus to the nucleus tractus solitarius (NTS) in the medulla. We investigated whether AVP acts in brain stem regions to influence sympathoadrenal outflow. Cannulae were implanted into the fourth ventricle of rats 7 days prior to the experiment. The effects of intracerebroventricular (icv) injections of AVP, the vehicle, and AVP antagonist, d(CH2)5Tyr(Me)AVP, on mean arterial pressure (MAP) and plasma noradrenaline (NA) and adrenaline (A) levels were determined in conscious unrestrained rats. Injections of AVP (icv, 23 and 73 ng/kg) but not the vehicle increased MAP and plasma NA and A levels. In contrast, iv injection of AVP increased MAP but decreased plasma concentrations of A and NA. The pressor response to icv injection of AVP was abolished by prior icv injection of AVP antagonist. Injection of AVP antagonist (icv, 0.5 and 1.5 microgram/kg) had no effect on MAP or plasma NA or A levels. These results show that centrally injected AVP activates sympathoadrenal outflow, possibly via an inhibition of baroreceptor reflexes. Since centrally administered AVP antagonist did not influence MAP or plasma NA or A levels, it appears that endogenously released AVP does not have a tonic influence on central cardiovascular reflex system in conscious, unrestrained rats.     

Vasopressin gene expression in the normal and Brattleboro rat: a histological analysis in semi-thin sections with biotinylated oligonucleotide probes

We analyzed expression of the vasopressin (AVP) gene in semi-thin sections in normal and Brattleboro rats by using in situ hybridization and immunohistochemistry. AVP mRNA was detected as follows: vibratome sections of rat hypothalamus were hybridized with a biotinylated oligonucleotide probe, embedded in Araldite, and cut into semi-thin sections which were reacted with streptavidin-alkaline phosphatase and the appropriate substrate. Adjacent serial sections were treated by immunohistochemistry to detect AVP or oxytocin immunoreactivity. In normal rat, AVP mRNA can be detected in magnocellular neurons of the supraoptic and paraventricular nuclei and in parvocellular neurons of the suprachiasmatic nucleus. AVP mRNA was present throughout the cytoplasm of the cell bodies, their processes, and in punctate structures in the vicinity of the AVP cell bodies. Most neurons containing AVP mRNA also contain AVP immunoreactivity, but the staining intensity was not consistently correlated for each reaction. A few neurons contained AVP mRNA without detectable AVP immunoreactivity. In the Brattleboro rat, staining intensity of the reaction was lower than in normal rat and the AVP mRNA was restricted mostly to the periphery of the cytoplasm. In this strain, the neurons containing the AVP mRNA did not contain AVP or oxytocin immunoreactivity. These results demonstrate that neuropeptide mRNA can be detected in semi-thin sections with a biotinylated oligonucleotide probe, and that AVP gene deletion provokes modification of the intracellular localization of the AVP mRNA.     

Identification and characterization of arginine vasopressin-like substances in the rat testis

We have previously demonstrated the suppression of Leydig cell steroidogenesis by arginine vasopressin (AVP) in vitro. Since the circulating level of AVP is too low to mediate a testicular action of this peptide, we have conducted studies to identify testicular AVP-like substances. The supernatant of homogenized, acid-extracted rat testes was found to contain AVP immunoreactivity which showed parallelism with synthetic AVP in a specific radioimmunoassay for AVP. Chromatography of this extract on a Sephadex G-25 column produced three peaks of AVP immunoreactivity. The largest peak eluted close to the column void volume, a second smaller peak eluted at the total column volume, while a third peak co-eluted with synthetic AVP. Following acetone precipitation, ether extraction, and octadecylsilica (C18) adsorption chromatography of the acid extract, the third peak of AVP immunoreactivity (about 600 pg/testis) was fully retained by C18 chromatography and showed parallelism with synthetic AVP in both radioimmuno- and radioreceptor assays. This substance also co-migrated with synthetic AVP on both Sephadex G-25 and reverse-phase thin layer chromatography (RPTLC). The second peak was only partially retained by C18 adsorption chromatography, dilution curves were not parallel with synthetic AVP in radioimmuno- or radioreceptor assay, and this material failed to co-migrate with synthetic AVP on Sephadex G-25 and RPTLC. The first peak of apparent AVP immunoreactivity was associated with an enzyme(s) that degraded labeled AVP. This enzymatic activity, as well as the immunoreactivity, could be eliminated by heating the extract to 90 degrees C. These results demonstrate, by a number of independent criteria, that rat testes contain a substance which behaves like authentic AVP. Due to its high concentration, the AVP-like peptide may be synthesized or concentrated by testis cells. In addition, testis tissue contains enzymatic activity which degrades AVP and could represent a site of regulation of AVP action. Coupled with the previously demonstrated testis action of AVP, these results suggest a paracrine or autocrine role of the neurohypophysial hormone at the testis level.     

Actin can act as a cofactor for a viral proteinase in the cleavage of the cytoskeleton

Cytoskeletal proteins are exploited by many viruses during infection. We report a novel finding that actin can act as a cofactor for the adenovirus proteinase (AVP) in the degradation of cytoskeletal proteins. Transfection studies in HeLa cells revealed AVP localized with cytokeratin 18, and this was followed by destruction of the cytokeratin network. For AVP to cleave cytokeratin 18, a cellular cofactor was shown to be required, consistent with AVP being synthesized as an inactive proteinase. Actin was considered a cellular cofactor for AVP, because the C terminus of actin is homologous to a viral cofactor for AVP. AVP was shown to bind to the C terminus of actin, and in doing so AVP exhibited full enzymatic activity. In vitro, actin was a cofactor in the cleavage of cytokeratin 18 by AVP. The proteinase alone could not cleave cytokeratin 18, but in the presence of actin, AVP cleaved cytokeratin 18. Indeed, actin itself was shown to be a cofactor and a substrate for its own destruction in that it was cleaved by AVP in vitro. Cleavage of cytoskeletal proteins weakens the structure of the cell, and therefore, actin as a cofactor may play a role in cell lysis and release of nascent virions.     

Neonatal exposure to vasopressin decreases vasopressin binding sites in the adult kidney

Previous experiments showed that rats injected with vasopressin (AVP) during the first seven days after birth were less sensitive as adults to the antidiuretic effects of AVP than were control rats. In the present experiment, binding sites for AVP were measured in the kidneys of similarly treated adult rats. Neonatal exposure to AVP significantly decreased the number of binding sites in the adults, but did not affect the binding affinity of the sites. It is concluded that neonatal exposure to AVP which produces a long-lasting decrease in responsiveness of the kidney to AVP is correlated with a reduction in the number of AVP binding sites in the tissue.     

Effect of intranasal arginine vasopressin on human headache

Arginine vasopressin (AVP), a nonapeptide hormone of posterior pituitary, reaches the central nervous system from systemic blood circulation with a difficulty because of the blood–brain barrier (BBB). The interest has been expressed in the use of the nasal route for delivery of AVP to the brain directly, exploiting the olfactory pathway. Our previous study has demonstrated that AVP in the brain rather than the spinal cord and blood circulation plays an important role in rat pain modulation. For understanding the role of AVP on pain modulation in human, the communication tried to investigate the effect of intranasal AVP on human headache. The results showed that (1) AVP concentration in both plasma and cerebrospinal fluid (CSF) increased significantly in headache patients, who related with the headache level; (2) there was a positive relationship between plasma and CSF AVP concentration in headache patients; and (3) intranasal AVP could relieve the human headache in a dose-dependent manner. The data suggested that intranasal AVP, which was delivered to the brain through olfactory region, could treat human headache and AVP might be a potential drug of pain relief by intranasal administration.     

Analysis of the vasopressin system and water regulation in genetically polydipsic mice

Polydipsic mice, STR/N, which show extreme polydipsia and polyuria, were discovered in 1958. In the STR/N, urine outputs are much higher than in control mice. The possibility of an abnormal regulation of the arginine vasopressin (AVP) system, or an abnormality in the renal susceptibility to AVP, should be considered. In this study we investigated the AVP system and water regulation in STR/N. We sequenced the AVP and the AVP V(2)-receptor genes of the STR/N by direct sequencing. No mutation was found in either of them. AVP gene expression examined by in situ hybridization and plasma sodium in 8-wk-old STR/N was significantly lower than in control mice, whereas it was significantly higher at 20 wk. Renal sensitivity to injected AVP was attenuated in 20-wk-old STR/N. The suppression of AVP synthesis due to excessive water retention in 8-wk-old STR/N suggests that polydipsia may be the primary cause in this strain. The 20-wk-old STR/N became dehydrated with the acceleration of AVP synthesis, which might have resulted from secondary desensitization to AVP.     

Arginine vasopressin inhibits apoptosis of rat glomerular mesangial cells via V1a receptors

Arginine vasopressin (AVP) promotes proliferation of glomerular mesangial cells. We examined whether AVP modulates an apoptosis of cultured rat glomerular mesangial cells at 3-17th passages. The agarose gel electrophoresis demonstrated that AVP attenuated a ladder formation stimulated by the serum deprivation. The quantitation of oligonucleosomes by ELISA also showed that AVP suppressed the serum deprivation-induced apoptosis. Such an antiapoptotic effect of AVP was dose-dependent. An AVP V1a receptor antagonist, d(CH2)5Tyr(Me)AVP, abolished the antiapoptotic effect of AVP. The inhibitory effect of AVP on the apoptosis was reduced by staurosporine and mimicked by phorbol-12-myristate-13-acetate. These results suggest that AVP inhibits serum deprivation-induced apoptosis of glomerular mesangial cells via V1a receptor-protein kinase C pathway.     

Central arginine vasopressin and endogenous antipyresis.

Arginine vasopressin (AVP) is a centrally synthesized nonapeptide that exerts classical endocrine effects as well as a host of centrally mediated actions. A strong case can be argued in support of a neurotransmitter-neuromodulator role for AVP. Acting within the central nervous system (CNS), AVP has been demonstrated to be involved in the modulation of febrile body temperature. Because AVP acts to reduce pyrogen-induced fevers, but not normal body temperature, its actions are deemed to be antipyretic. However, to demonstrate an endogenous antipyretic function, AVP must be shown to be active during conditions where fever is naturally suppressed. This review will focus on five such conditions where the absence of pyrogen-induced fever can be linked to the endogenous activity of AVP within the brain. In the neonatal rat pup, the use of specific antagonists to the AVP receptor has revealed a role for CNS AVP in the absence of fever following peripheral injections of bacterial endotoxin. These results may help to explain a similar lack of fever in other newborn species. In parturient animals a reduced or absent febrile response has been linked to the increased presence of AVP within the septal area of the brain. The combined use of AVP receptor antagonism as well as immunohistochemistry has shown enhanced AVP activity within the ventral septal area of the rat and guinea pig brain during tolerance to intravenous pyrogens. These results suggest that the mechanism of fever suppression following repeated systemic injections of bacterial pyrogen includes centrally acting AVP.(ABSTRACT TRUNCATED AT 250 WORDS)     

Organotypic Suprachiasmatic Nuclei Cultures of Adult Voles Reflect Locomotor Behavior: Differences in Number of Vasopressin Cells

This study is the first to demonstrate organotypic culturing of adult suprachiasmatic nuclei (SCN). This approach was used to obtain organotypic SCN cultures from adult vole brain with a previously determined state of behavioral circadian rhythmicity. We examined vasopressin (AVP) immunoreactivity in these organotypic slice cultures. AVP is one of the major neuropeptides produced by the SCN, the main mammalian circadian pacemaker. AVP immunoreactivity in the SCN of adult common voles in vivo has been shown to correlate with the variability in expression of circadian wheel-running behavior. Here, cultures prepared from circadian rhythmic and nonrhythmic voles were processed immunocytochemically for AVP. Whereas in all cultures AVP could be observed, AVP immunoreactivity differed considerably between vole SCN cultures. SCN cultures from rhythmic voles contained significantly lower numbers of AVP immunoreactive (AVPir) cells per surface area than cultures from nonrhythmic voles. The correlation between timing of behavior and AVP immunoreactivity in vitro is similar to the correlation found earlier in vivo. Apparently, such correlation depends on intrinsic AVP regulation mechanisms of SCN tissue, and not on neural or hormonal input from the environment, as present in intact brain.     

Effects of water immersion on arginine vasopressin release in humans

Since suppression of arginine vasopressin (AVP) appears to be a determinant of the diuresis of water immersion (WI) in humans, a further understanding of its responsiveness has important implications for normal physiology, pathophysiology, and space physiology. In recent years, discrepant measurements of AVP in plasma during WI have led to conflicting conclusions. In studies in which the subjects ingested water before or during WI, plasma AVP was reported to be unchanged or even increased. In contrast, plasma AVP was suppressed in studies in which the subjects remained hydropenic. A critical review discloses that water intake before and/or during the experiments introduces several new stimuli for AVP release. Furthermore the lower base-line levels of AVP in hydrated subjects complicate detection of small changes in plasma AVP. Although the mechanisms of AVP suppression during WI are incompletely defined, it appears that not only cardiopulmonary mechanoreceptors but also arterial baroreceptors mediate the response. Additional studies are proposed to delineate further the mechanisms governing AVP release during WI.     

Vasopressin release in response to hypovolaemia in the conscious rat and the effect of opioid and aminergic receptor antagonists.

Conscious rats were given i. p. polyethylene glycol (PEG) or dextran injections to compare their efficacy in inducing moderate hypovolaemia. Dextran was found unsuitable, producing large variability in the plasma vasopressin (AVP) concentrations. Putative neurotransmitters involved in the AVP response to hypovolaemia and in basal release were examined using opioid, and beta-adrenoceptor and dopamine receptor-blocking agents. A dose of PEG was chosen to produce a decrease in blood volume of approx 14.5% giving plasma AVP concentrations of 19.0 +/- 4.6 pmol/l. Naloxone and phenoxybenzamine failed to influence AVP release under both hypovolaemic and basal conditions. Prazosin also failed to influence the AVP response. In contrast propranolol elevated the plasma AVP concentrations in both conditions. Haloperidol enhanced basal AVP release but did not influence release during hypovolaemia. Guanethidine pretreatment partially blocked the response to hypovolaemia, but did not affect basal plasma AVP. Thus it appears that aminergic pathways have an inhibitory influence on AVP release under hypovolaemic and basal conditions. However, endogenous opioids do not appear to contribute significantly to the hypovolaemic response.     

Intraventricular administration of arginine vasopressin suppresses prolactin release via a dopaminergic mechanism

The present study was conducted to determine the effects of intracerebroventricular administration of arginine vasopressin (AVP) on the preovulatory prolactin (PRL) surge. Hourly injections of 1 or 5 micrograms AVP from 1200 to 1700 hr on proestrus prevented increases in plasma PRL levels that afternoon. However, following cessation of AVP treatment, a marked increase in PRL levels occurred between 1830 and 2030 hr. This "rebound" secretion of PRL was greater in rats given 5 micrograms AVP than in rats given the lower dose. The suppression of PRL release by AVP appears to be mediated by dopamine since 5 micrograms AVP failed to inhibit PRL release in animals pretreated with the dopamine antagonist domperidone. Interestingly, under these conditions, AVP increased PRL release compared to levels observed in saline-treated rats. In addition to suppressing PRL release, AVP exerted a dose-dependent inhibition of preovulatory LH release. The results suggest a possible interaction between AVP and dopamine in controlling PRL release which likely takes place within the median eminence.     

Raman and surface-enhanced Raman spectroscopy investigation of vasopressin analogues containing 1-aminocyclohexane-1-carboxylic acid residue

In this work, Raman spectroscopy (RS) was employed to characterize molecular structures of [Arg8]vasopressin (AVP) and its [Acc2,D-Arg8]AVP, [Acc3]AVP, and [Cpa1, Acc3]AVP analogues. The RS band assignments have been proposed. To determine the mechanism of adsorption of the above-mentioned compounds adsorbed on a colloidal silver surface, surface-enhanced Raman spectra (SERS) were measured. The SERS spectra were used to determine relative proximity of the adsorbed functional groups of [corrected] investigated peptides and their orientation on the silver surface. The AVP and [Acc3]AVP SERS spectra (Acc: 1-aminocyclohexane-1-carboxylic acid) show that the L-tyrosine (Tyr) lies far from the metal surface, whereas the [Cpa1,Acc3]AVP spectrum (Cpa: 1-mercaptocyclohexaneacetic acid) provides evidence that Tyr interacts with the silver surface. These results suggest that [corrected] the binding of the Tyr-ionized phenolic group might be responsible for the selectivity of the analogues. We show that the aromatic ring of L-phenylalanine (Phe) of AVP and [Acc2,D-Arg8]AVP interacts with the silver surface. The strength of this interaction is considerably weaker for [Acc2,D-Arg8]AVP than for AVP. This might be due either to a longer distance between the Phe ring and the silver surface, or to the almost perpendicular orientation of the Phe ring towards the surface. The carbonyl group of the L-glutamine [corrected] (Gln) or L-asparagine [corrected](Asn) of AVP, [Acc2,D-Arg8]AVP, and [Acc3]AVP is strongly bound to the silver surface. We have also found that all peptides adsorb on the silver surface via sulfur atoms of the disulfide bridge, adopting a "GGG" conformation, except [Cpa1,Acc3]AVP, which accepts a "TGG" geometry.