Neonatal CSF vasopressin concentration predicts later medical record diagnoses of autism spectrum disorder.

Autism spectrum disorder (ASD) is a brain disorder characterized by social impairments. ASD is currently diagnosed on the basis of behavioral criteria because no robust biomarkers have been identified. However, we recently found that cerebrospinal fluid (CSF) concentration of the "social" neuropeptide arginine vasopressin (AVP) is significantly lower in pediatric ASD cases vs. controls. As an initial step in establishing the direction of causation for this association, we capitalized upon a rare biomaterials collection of newborn CSF samples to conduct a quasi-prospective test of whether this association held before the developmental period when ASD first manifests. CSF samples had been collected in the course of medical care of 0- to 3-mo-old febrile infants (n = 913) and subsequently archived at -70 °C. We identified a subset of CSF samples from individuals later diagnosed with ASD, matched them 1:2 with appropriate controls (n = 33 total), and quantified their AVP and oxytocin (OXT) concentrations. Neonatal CSF AVP concentrations were significantly lower among ASD cases than controls and individually predicted case status, with highest precision when cases with comorbid attention-deficit/hyperactivity disorder were removed from the analysis. The associations were specific to AVP, as ASD cases and controls did not differ in neonatal CSF concentrations of the structurally related neuropeptide, OXT. These preliminary findings suggest that a neurochemical marker of ASD may be present very early in life, and if replicated in a larger, prospective study, this approach could transform how ASD is detected, both in behaviorally symptomatic children, and in infants at risk for developing it.

Cerebrospinal fluid vasopressin and symptom severity in children with autism.

Autism is a brain disorder characterized by social impairments. Progress in understanding autism has been hindered by difficulty in obtaining brain-relevant tissues (eg, cerebrospinal fluid [CSF]) by which to identify markers of disease and targets for treatment. Here, we overcome this barrier by providing evidence that mean CSF concentration of the "social" neuropeptide arginine vasopressin (AVP) is lower in children with autism versus controls. CSF AVP concentration also significantly differentiates individual cases from controls and is associated with greater social symptom severity in children with autism. These findings indicate that AVP may be a promising CSF marker of autism's social deficits. Ann Neurol 2018;84:611-615.

Participation of Antidiuretic Hormone (ADH) in Asthma Exacerbations Induced by Psychological Stress via PKA/PKC Signal Pathway in Airway-Related Vagal Preganglionic Neurons (AVPNs).

AIMS: Present study was performed to examine whether ADH was implicated in psychological stress asthma and to explore the underlying molecular mechanism. METHODS: We not only examined ADH levels in the cerebrospinal fluid (CSF) via radioimmunoassay, but also measured ADH receptor (ADHR) expression in airway-related vagal preganglionic neurons (AVPNs) through real-time PCR in all experimental mice. Western blotting was performed to evaluate the relationship between ADH and PKA/PKC in psychological stress asthma. Finally, the role of PKA/PKC in psychological stress asthma was analyzed. RESULTS: Marked asthma exacerbations were noted owing to significantly elevated levels of ADH and ADHR after psychological stress induction as compared to OVA alone (asthma group). ADHR antagonists (SR-49095 or SR-121463A) dramatically lowered higher protein levels of PKAα and PKCα induced by psychological stress as compared to OVA alone, suggesting the correlation between ADH and PKA/PKC in psychological stress asthma. KT-5720 (PKA inhibitor) and Go-7874 (PKC inhibitor) further directly revealed the involvement of PKA/PKC in psychological stress asthma. Some notable changes were also noted after employing PKA and PKC inhibitors in psychological stress asthma, including reduced asthmatic inflammation (lower eosinophil peroxidase (EPO) activity, myeloperoxidase (MPO) activity, immunoglobulin E (IgE) level, and histamine release), substantial decrements in inflammatory cell counts (eosinophils and lymphocytes), and decreased cytokine secretion (IL-6, IL-10, and IFN-γ), indicating the involvement of PKA/PKC in asthma exacerbations induced by psychological stress. CONCLUSION: Our results strongly suggested that ADH participated in psychological stress-induced asthma exacerbations via PKA/PKC signal pathway in AVPNs.

Arginine Vasopressin Is a Blood-Based Biomarker of Social Functioning in Children with Autism.

Brain arginine vasopressin (AVP) critically regulates normative social behavior in mammals, and experimental disruption of the AVP signaling pathway produces social impairments in rodent models. We therefore hypothesized that AVP signaling deficits may contribute to social impairments in children with autism spectrum disorder (ASD). Since blood measures (which are far easier to obtain than brain measures) of AVP are most meaningful if they are related to brain AVP activity, Study 1 tested the relationship between AVP concentrations in concomitantly collected blood and CSF samples from children and adults (N = 28) undergoing clinical procedures. Study 2 tested whether blood AVP concentrations: 1) differed between children with ASD (N = 57), their ASD discordant siblings (N = 47), and neurotypical controls (N = 55); and 2) predicted social functioning (using the NEPSY-II Theory of Mind and Affect Recognition tasks and the Social Responsiveness Scale) in this large, well-characterized child cohort. Blood AVP concentrations significantly and positively predicted CSF AVP concentrations (F1,26 = 7.17, r = 0.46, p = 0.0127) in Study 1. In Study 2, blood AVP concentrations did not differ between groups or by sex, but significantly and positively predicted Theory of Mind performance, specifically in children with ASD, but not in non-ASD children (F1,144 = 5.83, p = 0.017). Blood AVP concentrations can be used: 1) as a surrogate for brain AVP activity in humans; and 2) as a robust biomarker of theory of mind ability in children with ASD. These findings also suggest that AVP biology may be a promising therapeutic target by which to improve social cognition in individuals with ASD.

Plasma vasopressin concentrations positively predict cerebrospinal fluid vasopressin concentrations in human neonates.

Central arginine vasopressin (AVP) plays a critical role in mammalian social behavior and has been hypothesized to be a biomarker of certain human neurodevelopmental disorders, including autism. However, opportunities to collect post-mortem brain tissue or cerebrospinal fluid (CSF) from children are extremely limited, and the use of less invasive peripheral assessments (e.g., blood, urine, or saliva) of AVP as a proxy for more invasive central measures has not been well validated. Further, almost nothing is known about AVP biology in very young infants. Therefore in the present study we concomitantly collected basal CSF and plasma samples from N = 20 neonates undergoing clinical sepsis evaluation (all were sepsis negative) and quantified AVP concentrations via well-validated enzyme-immunoassay methodology. Plasma AVP concentrations significantly and positively predicted CSF AVP concentrations (r = 0.73, p = 0.0021), and this relationship persisted when variance attributed to sex, gestational age, and sample collection time was controlled for in the statistical model (r = 0.75, p = 0.0047). These findings provide preliminary support for the use of basal plasma AVP measurement as a proxy for basal brain AVP activity in pediatric populations. Future studies are now required to determine the relationship between behavioral measures and AVP concentrations in both central and peripheral compartments in young infants and older children.

Vasopressin and oxytocin in CSF and plasma of patients with aneurysmal subarachnoid haemorrhage.

OBJECTIVE: Clinicopathological studies on patients succumbing to subarachnoid haemorrhage (SAH) demonstrated hypothalamic lesions. The implication of the hypothalamic neuropeptides arginine-vasopressin (AVP) and oxytocin (OXT) has not been linked to aneurysmal SAH yet. This study investigates AVP and OXT in CSF and plasma of patients with spontaneous aneurysmal SAH and their association with outcome. METHODS: CSF and plasma samples of 12 patients with aneurysmal SAH were prospectively studied for 2weeks. AVP and OXT were measured by radioimmunoassay. Outcome was assessed on Glasgow-Outcome-Scale. Twenty-nine patients without neuropsychiatric disturbances served as controls. Differences in neuropeptide concentration time courses were assessed by regression models. Group comparisons were performed by Kruskal-Wallis and correlations by Spearman tests. RESULTS: Regression of CSF levels between patients with poor and good outcome revealed significantly lower levels of AVP in patients with poor outcome (p=0.012) while OXT showed a trend towards lower levels (p=0.063). In plasma, no significant differences between outcome groups were found. Group comparisons between poor outcome patients and controls revealed significant differences in CSF for AVP (p=0.001) and OXT (p=0.015). In plasma, AVP yielded significantly different results while OXT did not. No differences were found between the good outcome group and controls. Plasma and CSF concentrations showed no significant correlation. CONCLUSION: Patients with poor outcome after aneurysmal SAH have lower AVP and OXT levels in CSF than patients with good outcome while neuropeptide levels in plasma failed to reflect differences in outcome. The data indicate hypothalamic damage as an aetiologic factor for outcome after aneurysmal SAH.

Increased intracranial pressure is associated with elevated cerebrospinal fluid ADH levels in closed-head injury.

OBJECTIVES: Head injury frequently results in increased intracranial pressure and brain edema. Investigators have demonstrated that ischemic injury causes an increase in cerebrospinal fluid (CSF) levels of antidiuretic hormone (ADH); increased CSF ADH levels exacerbate cerebral edema, and inhibition of the ADH system with specific ADH antagonists reduces cerebral edema. The current study was designed to test the hypothesis that elevated levels of ADH are present in the CSF of subjects with head injury. METHODS: Ventricular CSF and blood samples were taken from 11 subjects with head injury and 12 subjects with no known head trauma or injury. ADH levels were analyzed using radioimmunoassay. Severity of increased intracranial pressure (ICP) was rated in head-injured subjects using a four-point ordinal scale, based on which treatments were necessary to reduce ICP. RESULTS: Subjects with head injury had higher CSF (3.2 versus 1.2 pg/ml; P<0.02) and plasma (4.1 versus 1.4 pg/ml; P<0.02) levels of ADH than did control subjects. In head-injured subjects, CSF ADH levels positively correlated with severity of ICP. DISCUSSION: The results of this study suggest that ADH plays a role in brain edema associated with closed head injury.

Concentrations of ketone body and antidiuretic hormone in cerebrospinal fluid in response to the intra-ruminal administration of butyrate in suckling calves.

The aim of the present study was to elucidate the mechanism by which ketone bodies increase antidiuretic hormone (ADH) secretion. Four male Holstein calves (5 weeks of age) were utilized. Four levels of butyrate (0 g, 11 g, 22 g and 44 g) were administrated intra-ruminally in a 4 x 4 Latin square design and cerebrospinal fluid (CSF, six-position lumbar puncture), blood plasma and urine were collected. The concentration of total plasma and CSF protein was 5.5-5.6 g/dL and 27.5-28.3 mg/dL, respectively. CSF concentrations of a specific ketone body, 3-hydroxybutyric acid, were significantly higher in the 22 g and 44 g butyrate groups than in the control group. CSF concentrations of ADH in the 11 g and 44 g butyrate groups were significantly higher than in the control group. Plasma concentration of 3-hydroxybutyric acid was increased by intraruminal administration of butyrate within 15 min in a dose-dependent manner, and it was higher in the 22 g and 44 g butyrate group than in the control group from 15 min to 4 h. With the exception of the 11 g butyrate group, plasma concentrations of ADH also increased in response to butyrate treatment, and it was higher in the 44 g butyrate group than in the 22 g butyrate group from 15 min to 1.5 h. The duration of the elevated plasma concentrations of ADH was shorter than that of the plasma concentration of 3-hydroxybutyric acid. The relationship between the plasma concentrations of ADH and 3-hydroxybutyric acid was statistically significant but the correlation between the two concentrations was not high. Butyrate treatment elevated the plasma concentration of ADH and also resulted in reduced urine volume and increased urine osmolality. Haematocrit (Ht) values, and the osmolality of CSF and plasma were not different among the groups. Our results suggested that the increased ADH secretion observed in suckling calves fed dry feeds was caused by butyrate-derived ketone body that crossed the blood-brain barrier rapidly.

Vasopressin and oxytocin release into CSF after sympathetic stimulation in rat.

Vasopressin and oxytocin are neurohormones of the posterior pituitary lobe released not only into the blood, but also into cerebrospinal fluid (CSF). Posterior pituitary lobe has central and peripheral noradrenergic innervation; peripheral origins from superior cervical ganglia (SCG) (Alper et al. 1980; Saavedra 1986). It is known, that sympathetic nervous system is involved in vasopressin (AVP) and oxytocin (OXY) release from neurohypophysis into the blood (Romeo et al. 1991; Lipinska et al. 1996). The factors which stimulate neurohormones release into the blood do not always cause their release into CSF (Dogterom et al. 1977; Szczepanska-Sadowska et al. 1983). The aim of this study was to elucidate the question whether the stimulation of preganglionic fibers of the SCG could influence the release of AVP and OXY into CSF.

Vasopressin and oxytocin release within the brain: a dynamic concept of multiple and variable modes of neuropeptide communication.

As exemplified particularly with vasopressin and oxytocin, release of neuropeptides within the brain occurs from dendrites, somata, and axons of neurosecretory neurons; mechanisms include activation of intracellular Ca2+ stores, changed strength of synaptic input and altered interaction between transcription factors and gene promoters. Upon demand, both diffuse spread of neuropeptides in the extracellular fluid following dendritic release and focal release from axonal terminals may contribute to regionally and temporally varying combinations of neuromodulator and neurotransmitter actions, thus providing a theoretically unlimited variability in interneuronal signaling. Thus, instead of favoring volume or synaptic transmission following central neuropeptide release, a more dynamic concept is presented with multiple and variable modes of release and communication. This concept considers neuropeptides in the extracellular fluid of the brain rather than those in the cerebrospinal fluid or plasma as primary signals, triggering a variety of receptor-mediated effects, including those underlying behavioral and neuroendocrine regulation and psychopathology.

Fear and power-dominance motivation: proposed contributions of peptide hormones present in cerebrospinal fluid and plasma.

We propose that fear and power-dominance drive motivation are generated by the presence of elevated plasma and cerebrospinal fluid (CSF) levels of certain peptide hormones. For the fear drive, the controlling hormone is corticotropin releasing factor, and we argue that elevated CSF and plasma levels of this peptide which occur as a result of fear-evoking and other stressful experiences in the recent past are detected and transduced into neuronal activities by neurons in the vicinity of the third ventricle, primarily in the periventricular and arcuate hypothalamic nuclei. For the power-dominance drive, we propose that the primary signal is the CSF concentration of vasopressin, which is detected in two circumventricular organs, the subfornical organ and organum vasculosum of the lamina terminalis. We suggest that the peptide-generated signals detected in periventricular structures are transmitted to four areas in which neuronal activities represent fear and power-dominance: one in the medial hypothalamus, one in the dorsolateral quadrant of the periaqueductal gray matter, a third in the midline thalamic nuclei, and the fourth within medial prefrontal cortex. The probable purpose of this system is to maintain a state of fear or anger and consequent vigilant or aggressive behavior after the initial fear- or anger-inducing stimulus is no longer perceptible. We further propose that all the motivational drives, including thirst, hunger and sexual desire are generated in part by non-steroidal hormonal signals, and that the unstimulated motivational status of an individual is determined by the relative CSF and plasma levels of several peptide hormones.

Cerebrospinal fluid corticotropin-releasing factor (CRF) and vasopressin concentrations predict pituitary response in the CRF stimulation test: a multiple regression analysis.

There is considerable evidence that stress-related psychiatric disorders, including depression and post-traumatic stress disorder (PTSD), are associated with hypersecretion of corticotropin-releasing factor (CRF) within the central nervous system (CNS). One line of evidence that is consistent with central CRF hypersecretion in these disorders is the blunted adrenocorticotropin hormone (ACTH) response to intravenous CRF administration, likely a consequence, at least in part, of downregulation of anterior pituitary CRF receptors. The present study tests the hypothesis that elevated cerebrospinal fluid (CSF) concentrations of CRF and a secondary ACTH secretagogue, arginine vasopressin (AVP), are associated with diminished adenohypophyseal responses in a standard CRF stimulation test. CSF concentrations of CRF and AVP, and plasma ACTH responses to the administration of 1 microg/kg ovine CRF (oCRF) were measured in healthy adult women with and without current major depression and/or a history of significant childhood abuse. The primary outcome measure was ACTH area under the curve (AUC) in the CRF stimulation test. Multiple linear regression was performed to identify the impact of CSF CRF and AVP concentrations upon the pituitary response to CRF stimulation. The regression model explained 56.5% of the variation in the ACTH response to CRF stimulation. The relationship of CSF concentrations of CRF to ACTH responses to CRF were best described by a third-order function that was inversely correlated over most of the range of studied values. The association of ACTH response with CSF concentration of AVP and the dose of oCRF followed second-order kinetics. These findings support the hypothesis that central CRF hypersecretion is associated with a blunted ACTH response to exogenously administered CRF, explaining almost 60% of the variation in the ACTH response to CRF.

Vasopressin as a target for antidepressant development: an assessment of the available evidence.

Hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis is one of the key biological abnormalities described in major depressive disorder, occurring in 30-50% of depressed subjects. Corticotropin-releasing hormone (CRH) and vasopressin (AVP) are the main regulators of this stress system, with the two neuropeptides acting synergistically in bringing about adrenocorticotropin (ACTH) release from the anterior pituitary and cortisol from the adrenal gland. Based on the demonstration of elevated cerebrospinal fluid levels of CRH in depressives, and other evidence, it has been postulated that excess CRH and the resultant increased HPA forward drive form the basis of neuroendocrine dysregulation in depression. However, there is an accumulating body of evidence to support a significant role for AVP in the regulation of pituitary-adrenal activity in health and also in depressive disorder. This review, based on a Medline search from 1980 to 2001, focuses on the functional neuroanatomy, receptor pharmacology, VP synergism with CRH, and the data from clinical and pre-clinical studies that support an important role for AVP in the pathophysiology of major depression. We suggest that future antidepressants may target the vasopressinergic system.

CSF oxytocin and vasopressin levels after recovery from bulimia nervosa and anorexia nervosa, bulimic subtype.

BACKGROUND: When ill, people with eating disorders have disturbances of the neuropeptides vasopressin and oxytocin. METHODS: To avoid the confounding effects of the ill state, we studied women who were recovered (more than 1 year, normal weight, and regular menstrual cycles, no bingeing or purging) from bulimia nervosa (rBN) or binge eating/purging-type anorexia nervosa (rAN-BN), and matched healthy control women. RESULTS: Vasopressin was elevated in rAN-BN and showed a trend towards elevation in rBN. In rBN, elevated cerebrospinal fluid vasopressin may be related to having a lifetime history of major depression. In comparison, cerebrospinal fluid oxytocin was normal in recovered subjects, but elevated levels in some rBN might be related to birth control pill use. CONCLUSIONS: These data confirm and extend the possibility that elevated cerebrospinal fluid vasopressin may be related to the pathophysiology of eating disorders, and/or a lifetime history of major depression.

Central action of nitric oxide in the saltwater-acclimated duck: modulation of extrarenal sodium excretion and vasotocin release.

Hypothalamic nuclei close to the third ventricle (VIII) represent key structures in avian osmoregulation concerned with the control of salt gland activity and release of the antidiuretic hormone [Arg8]vasotocin (AVT). Nitric oxide (NO) acting as a paracrine transmitter in the hypothalamus has been shown to contribute to the maintenance of salt and fluid balance in mammals. The saltwater-acclimated duck was used in the present study as a well-characterized osmoregulatory model to investigate the role of central NO in hypothalamic perception or integration of osmoregulatory signals in marine birds. During osmotically induced steady-state salt gland secretion, the VIII of conscious ducks was microperfused with artificial cerebrospinal fluid (aCSF) alone, aCSF containing the NO-donor SNAP or the peptide [Val5]angiotensin II (ANGII) and alterations in salt gland activity, arterial pressure and the release of AVT were continuously monitored. No changes occurred during intracerebroventricular microperfusion with aCSF. Central application of ANGII, a known inhibitory hypothalamic transmitter in the control of salt gland function, markedly blocked salt gland osmolal excretion. Central stimulation with the NO-donor SNAP significantly reduced osmolal excretion from 0.41+/-0.02 to 0. 22+/-0.04 mosmol/min. Both ANGII and SNAP caused a rise in plasma AVT at either slightly elevated (ANGII) or constant (SNAP) arterial pressure. Employing NADPH-diaphorase histochemistry in the duck hypothalamus to localize sites of NO synthesis, periventricular neurons, nerve fibers in close association to the VIII and also parvocellular neurons of the paraventricular nucleus could be labeled. These data suggest a modulatory role for hypothalamic NO within the central osmoregulatory circuitry controlling salt gland function and AVT release in marine birds.

Circadian rhythmicity of vasopressin levels in the cerebrospinal fluid of suprachiasmatic nucleus-lesioned and -grafted rats.

Transplantation of the fetal suprachiasmatic nucleus (SCN) in arrhythmic SCN-lesioned rats can reinstate circadian drinking rhythms in 40% to 50% of the cases. In the current article, it was investigated whether the failure in the other rats could be due to the absence of a circadian rhythm in the grafted SCN, using a circadian vasopressin (VP) rhythm in the cerebrospinal fluid (CSF) as the indicator for a rhythmic SCN. CSF was sampled in continuous darkness from-intact control rats and SCN-lesioned and -grafted rats. VP could be detected in all samples, with concentrations of 15 to 30 pg/ml in the control rats and 5 to 15 pg/ml in the grafted rats. A circadian VP rhythm with a two- to threefold difference between peak and nadir values was found in all 7 control rats but in only 4 of 13 experimental rats, despite the presence of a VP-positive SCN in all grafts. A circadian VP rhythm was present in 2 drinking rhythm-recovered rats (6 of 13) and in 2 nonrecovery rats. Apparently, in these latter rats, the failure of the grafted SCN to restore a circadian drinking rhythm cannot be attributed to a lack of rhythmicity in the SCN itself. Thus, the presence of a rhythmic grafted SCN, as is deduced from a circadian CSF VP rhythm, appears not to be sufficient for restoration of a circadian drinking rhythm in SCN-lesioned arrhythmic rats.

Cerebrospinal fluid concentrations of corticotropin-releasing hormone, vasopressin, and somatostatin in depressed patients and healthy controls: response to amitriptyline treatment.

The effect of amitriptyline upon hypothalamic-pituitary-adrenal [HPA]-system-regulating neuropeptides (corticotropin-releasing hormone [CRH], vasopressin, somatostatin) was studied in a group of depressed elderly patients and controls. A first lumbar puncture was performed in 37 depressed in-patients. This was followed by a 6-week medication phase with amitriptyline. Upon its completion a second cerebrospinal fluid (CSF) sample was obtained in 18 of these 37 patients. In 25 healthy controls a first lumbar puncture was done eleven of these individuals agreed to take 75 mg/d amitriptyline for 6 weeks and to participate in the follow-up CSF study. Within the group of depressed patients amitriptyline led to a significant decrease of CSF CRH in treatment responders only (F1, 16 = 5.2; P < 0.02). Also, in normal controls CSF CRH concentration tended to decrease with amitriptyline treatment (t-test; P < 0.09). No effects of amitriptyline upon vasopressin or somatostatin were observed. In normal controls (r = 0.4; P < 0.02) and in patients (r = 0.4; P < 0.03) age correlated positively with baseline CSF somatostatin. A trend for CSF CRH to increase with aging was found only in controls (r = 0.3; P < 0.09); patients did not show a significant association here. Finally, CSF neuropeptide concentration at baseline did not differ between the group of depressed patients and healthy controls. Our study corroborates the evolving concept that antidepressants effect various components of the HPA system with the net result of a reduction in its activity. In addition, we found CSF CRH and CSF somatostatin concentrations to be better reflections of age than of depression and, finally, that during aging and during depression the HPA system changes in similar directions.

Relationship between vasopressin and opioids in hypoxia induced pial artery vasodilation.

It has been observed that a vasopressin receptor antagonist attenuates hypoxic hyperemia in fetal sheep, whereas methionine enkephalin (Met) and leucine enkephalin (Leu) contribute to hypoxia-induced pial artery dilation in newborn pigs. This study was designed to investigate the relationship between vasopressin and opioids in hypoxia-induced pial artery dilation in the newborn pig by use of the closed cranial window technique. Hypoxia-induced pial artery dilation was attenuated during moderate [arterial Po2 (PaO2) approximately 35 mmHg] and severe hypoxia (PaO2 approximately 25 mmHg) by the vasopressin receptor antagonist, [beta-mercapto-beta beta-cyclopentamethylenepropionyl, 2-O-Me-Tyr2, Arg8]vasopressin (MeAVP, 5 micrograms/kg i.v.; 29 +/- 1 vs. 14 +/- 2 and 37 +/- 2 vs. 18 +/- 2% for moderate and severe hypoxia in absence vs. presence of MeAVP, respectively, n = 7). Hypoxia-induced dilation was accompanied by increased cerebrospinal fluid (CSF) vasopressin concentration (26 +/- 1 vs. 67 +/- 4 and 26 +/- 1 vs. 99 +/- 4 pg/ml for control vs. moderate and control vs. severe hypoxia, n = 5). Vasopressin increased CSF Met (895 +/- 28, 1,147 +/- 63, 1,327 +/- 48, and 1,600 +/- 75 pg/ml for control and 40, 400, and 4,000 pg/ml vasopressin, respectively, n = 7). CSF Leu concentration was similarly increased by vasopressin. Furthermore, MeAVP attenuated the release of Met during moderate hypoxia (910 +/- 38 and 2,682 +/- 49 vs. 911 +/- 38 and 2,110 +/- 84 pg/ml for control and moderate hypoxia in absence and presence of MeAVP, respectively, n = 5). MeAVP had similar effects on hypoxia-induced Leu release. These data show that vasopressin contributes to hypoxia-induced pial artery dilation and that vasopressin increases CSF Met and Leu concentrations. These data also suggest that elevated CSF vasopressin concentrations that occur during hypoxemia result in opioid release, which subsequently contributes to hypoxic pial artery dilation.