Testosterone enhancement during pregnancy influences social coping and gene expression of oxytocin and vasopressin in the brain of adult rats

Steroid hormones are important mediators of prenatal maternal effects and play an important role in fetal programming. The aim of our study was to investigate how testosterone enhancement during pregnancy influences neurobehavioral aspects of social coping of rat offspring in adulthood. Pregnant rat dams were exposed to depot form of testosterone during the last third of pregnancy (i.e., beginning on the 14th day of pregnancy). Their adult offspring were later tested in a social interaction test and expression of oxytocin and arginine-vasopressin mRNA in the hypothalamic nuclei was evaluated. Our research showed that prenatal exposure to higher levels of testosterone activated socio‑cohesive and socio‑aversive interactions, but only in males. The testosterone‑exposed group also showed decreased oxytocin mRNA expression in the supraoptic and paraventricular nuclei of the hypothalamus, and increased arginine-vasopressin mRNA expression in the supraoptic and suprachiasmatic nuclei as compared to controls. However, we did not observe any sex differences in the expression of oxytocin and arginine‑vasopressin mRNA in these regions. Our findings show that testosterone enhancement in pregnancy could have long‑lasting effects on oxytocin and arginine-vasopressin levels in the brain of adult animals, but lead to changes in behavioral aspects of coping strategies only in males.

Diagnosis and management of hyponatremia in cancer patients

Hyponatremia, a common electrolyte abnormality in oncology practice, may be a negative prognostic factor in cancer patients based on a systematic analysis of published studies. The largest body of evidence comes from small-cell lung cancer (SCLC), for which hyponatremia was identified as an independent risk factor for poor outcome in six of 13 studies. Hyponatremia in the cancer patient is usually caused by the syndrome of inappropriate antidiuretic hormone (SIADH), which develops more frequently with SCLC than with other malignancies. SIADH may be driven by ectopic production of arginine vasopressin (AVP) by tumors or by effects of anticancer and palliative medications on AVP production or action. Other factors may cause hypovolemic hyponatremia, including diarrhea and vomiting caused by cancer therapy. Hyponatremia may be detected on routine laboratory testing before or during cancer treatment or may be suggested by the presence of mostly neurological symptoms. Treatment depends on several factors, including symptom severity, onset timing, and extracellular volume status. Appropriate diagnosis is important because treatment differs by etiology, and choosing the wrong approach can worsen the electrolyte abnormality. When hyponatremia is caused by SIADH, hypertonic saline is indicated for acute, symptomatic cases, whereas fluid restriction is recommended to achieve a slower rate of correction for chronic asymptomatic hyponatremia. Pharmacological therapy may be necessary when fluid restriction is insufficient. The orally active, selective AVP receptor 2 (V(2))-receptor antagonist tolvaptan provides a mechanism-based option for correcting hyponatremia caused by SIADH or other conditions with inappropriate AVP elevations. By blocking AVP effects in the renal collecting duct, tolvaptan promotes aquaresis, leading to a controlled increase in serum sodium levels.

Gestational valproate alters BOLD activation in response to complex social and primary sensory stimuli

Valproic acid (VPA) has been used clinically as an anticonvulsant medication during pregnancy; however, it poses a neurodevelopmental risk due to its high teratogenicity. We hypothesized that midgestational (GD) exposure to VPA will lead to lasting deficits in social behavior and the processing of social stimuli. To test this, animals were given a single IP injection of 600 mg/kg of VPA on GD 12.5. Starting on postnatal day 2 (PND2), animals were examined for physical and behavior abnormalities. Functional MRI studies were carried out after PND60. VPA and control animals were given vehicle or a central infusion of a V_1a antagonist 90 minutes before imaging. During imaging sessions, rats were presented with a juvenile test male followed by a primary visual stimulus (2 Hz pulsed light) to examine the effects of prenatal VPA on neural processing. VPA rats showed greater increases in BOLD signal response to the social stimulus compared to controls in the temporal cortex, thalamus, midbrain and the hypothalamus. Blocking the V_1a receptor reduced the BOLD response in VPA animals only. Neural responses to the visual stimulus, however, were lower in VPA animals. Blockade with the V_1a antagonist did not revert this latter effect. Our data suggest that prenatal VPA affects the processing of social stimuli and perhaps social memory, partly through a mechanism that may involve vasopressin V_1a neurotransmission.

Plasma arginine vasopressin level in hypothyroid women in relation to dietary sodium supply

INTRODUCTION

A disturbed regulation mechanism of arginine vasopressin secretion in response to plasma osmolality and volaemia changes occurs in hypothyroidism. The aim of this study was to determine plasma arginine vasopressin concentration in hypothyroid women under conditions of a low sodium diet and in an upright position.

MATERIAL AND METHODS

Twenty-six women with primary hypothyroidism and 24 healthy women (control group) were investigated. In all the patients, the plasma arginine vasopressin and serum sodium and potassium levels, as well as plasma osmolality, were measured first under basal conditions, i.e. after three days of a normal sodium diet (120 mmol sodium per day) in a horizontal position, and next after three days of a low sodium diet (10 mmol Na per day) in an upright position. In hypothyroid patients, the investigations were repeated after a euthyroid state as a result of L-thyroxine treatment had been attained.

RESULTS

An increase of vasopressinaemia, measured under basal conditions as well as after three days of the low sodium diet, was shown in untreated hypothyroid patients compared to the control group. The arginine vasopressin plasma level normalised after a euthyroid state had been attained. As a result of the low sodium diet and the upright position, a significant increase of arginine vasopressin secretion was observed in the control group and hypothyroid women in the euthyroid state. No significant increase of this neuropeptide level in untreated patients was shown while applying the low sodium diet and upright position. Plasma osmolality and natraemia were decreased in the untreated hypothyroid patients. No correlation between vasopressinaemia and plasma osmolality was shown.

CONCLUSION

The plasma arginine vasopressin level is increased in hypothyroid women, and does not change in the upright position under the influence of a low sodium diet.

Binge-pattern alcohol exposure during puberty induces sexually dimorphic changes in genes regulating the HPA axis

Maternal alcohol consumption during critical periods of fetal brain development leads to devastating long-term consequences on adult reproductive physiology, cognitive function, and social behaviors. However, very little is known about the long-term consequences of alcohol consumption during puberty, which is perhaps an equally dynamic and critical period of brain development. Alcohol abuse during adulthood has been linked with an increase in clinically diagnosed anxiety disorders, yet the etiology and neurochemical mechanisms of alcohol-induced anxiety behavior is unknown. In this study, we determined the effects of binge ethanol exposure during puberty on two critical central regulators of stress and anxiety behavior: corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP). Our results showed that ethanol increased plasma corticosterone (CORT) levels in both sexes, yet binge-treated animals had significantly lower CORT levels than animals exposed to a single dose, suggesting that the hypothalamo-pituitary-adrenal (HPA) axis habituated to the repeated stressful stimuli of ethanol. Binge ethanol exposure also significantly increased CRH and AVP gene expression in the paraventricular nucleus of males, but not females. Overall, our results demonstrate that binge ethanol exposure during puberty changes the central expression of stress-related genes in a sex-specific manner, potentially leading to permanent dysregulation of the HPA axis and long-term behavioral consequences.

Pharmacokinetic and pharmacodynamic interaction between tolvaptan, a non-peptide AVP antagonist, and furosemide or hydrochlorothiazide

The pharmacokinetic and pharmacodynamic interactions between tolvaptan and furosemide or hydrochlorothiazide (HCTZ) were determined in a single-center, randomized, open-label, parallel-arm, 3-period crossover study conducted in healthy white (Caucasian) men. A total of 12 subjects were enrolled in the study, with 6 subjects assigned to each of two treatment arms. Subjects in Arm 1 received 30 mg of tolvaptan, 80 mg of furosemide, and 30 mg of tolvaptan + 80 mg of furosemide. Subjects in Arm 2 received 30 mg of tolvaptan, 100 mg of HCTZ, and 30 mg pf tolvaptan + 100 mg of HCTZ. Doses were separated by a 48-hour washout. Blood and urine samples were collected at scheduled timepoints during the 24 hours after administration of study drug for the determination of pharmacokinetic and pharmacodynamic parameters. No clinically significant changes were noted in the pharmacokinetic profiles of tolvaptan and furosemide or tolvaptan and HCTZ when coadministered. Free water clearance, 24-hour urine volume, plasma sodium and argentine vasopressin concentrations, and plasma osmolality were higher, and urine osmolality was lower when tolvaptan was administered either alone or in combination with furosemide or HCTZ, compared with furosemide or HCTZ administered alone. At 24 hours postdose, plasma renin activity was increased after furosemide or HCTZ administered alone or with tolvaptan, but it was unchanged after tolvaptan alone. Tolvaptan did not significantly affect the natriuretic activity of furosemide or HCTZ. Furosemide and HCTZ did not significantly affect the aquaretic activity of tolvaptan. Tolvaptan administered alone or in combination with furosemide or HCTZ was safe and well tolerated at the given doses.

?-Amino Butyric Acid Control of Arginine Vasopressin Release from the Ewe Hypothalamus In Vitro: Sensitivity to Oestradiol

The present study aims to ascertain the influence of gamma-amino butyric acid (GABA)(A or B) receptors on arginine vasopressin (AVP) release in vitro and determine whether E(2) modulates GABA-AVP interaction. Within 10 min of ewe killing, saggital midline hypothalamic slices (from the anterior preoptic area to the mediobasal hypothalamus along with the median eminence, 2-mm thick, two per ewe) were dissected, placed in oxygenated minimum essential media (MEM)-alpha at 4 degrees C and within 2 h were singly perifused at 37 degrees C with oxygenated MEM-alpha (pH 7.4; flow rate 0.15 ml/min), either with or without E(2) (24 pg/ml). After 4-h equilibration, 10-min fractions were collected for 4 h interposed with a 10-min exposure at 60 min to a specific GABA(A or B) receptor agonist or antagonist at various doses (0.1-10 mm). GABA(A) (muscimol; no E(2), n = 7 perifusion chambers, with E(2), n = 11) or GABA(B) (baclofen; no E(2), n = 8, with E(2), n = 15) agonists (10 mm) did not influence AVP concentrations. However, AVP release increased (p < 0.05) 20-30 min after exposure to 10 mm GABA(A or B) antagonists (bicuculline, no E(2), n = 7: from 4.6 +/- 0.7 to 33.0 +/- 0.4, with E(2), n = 17: from 11.9 +/- 1.4 to 32.8 +/- 6.0; CGP52432, with E(2), n = 14: from 14.0 +/- 2.6 to 28.8 +/- 3.9 pg/ml). At the end of the collection period, hypothalamic slices responded to KCl (100 mm) with AVP efflux (p < 0.05). GABA(B) but not GABA(A) antagonist-stimulated AVP release was enhanced in the presence of E(2). In summary, AVP release is under the inhibitory influence of GABA input with further potentiation by E(2) through GABA(B) receptors in vitro.

Recognition and treatment of hyponatremia in acutely ill hospitalized patients

OBJECTIVE

The objective of this paper was to discuss the diagnosis, pathophysiology, and management of hyponatremia among critically ill, hospitalized patients (eg, after surgery or in the intensive care unit).

METHODS

English-language literature published between 1967 and 2006 was searched using several key words (AVP receptor antagonists, hyponatremia, SIADH, conivaptan, tolvaptan, and lixivaptan) and by accessing MEDLINE and ScienceDirect. Meeting abstracts from scientific sessions (American Society of Nephrology Renal Week 2004 and the Endocrine Society's 87th Annual Meeting [2005]) were reviewed. The package insert for conivaptan hydrochloride injection was referenced from . Clinical trials included in this review were randomized and placebo controlled.

RESULTS

Based on the literature we researched, hyponatremia is the most common electrolyte disorder encountered in critical care and is associated with a variety of conditions, including congestive heart failure and the syndrome of inappropriate antidiuretic hormone secretion. Because hyponatremia can arise in hypervolemic, euvolemic, and hypovolemic states, clinicians may not recognize its presence and cause. Incorrect management can lead to significant morbidity and mortality. Physicians need to recognize risk factors and symptoms and use appropriate treatment guidelines for hyponatremia. Traditionally, therapy for hyponatremia has been limited by efficacy and safety concerns. Arginine vasopressin (AVP) receptor antagonists, therapeutic agents that promote aquaresis in patients with hyponatremia by targeting V(1a) receptors in the vascular smooth muscle, V(2) receptors in the kidney, or both, are under development. A dual-receptor antagonist targeting both V(1a) and V(2) receptors is now approved for the treatment of euvolemic hyponatremia in hospitalized patients.

CONCLUSIONS

Hyponatremia, an electrolyte abnormality found in critically ill patients, can be associated with significant morbidity and mortality. AVP receptor antagonists show promise as effective and tolerable treatments for patients with hyponatremia.

Lithium, arginine vasopressin and the dex/CRH test in mood disordered patients

The impact of lithium on arginine vasopressin (AVP) release has implications for our understanding of the pathophysiology and treatment of mood disorders and for the interpretation of neuroendocrine studies. In this secondary analysis of neuroendocrine, data from 23 patients with chronic major depressive disorder, 41 patients with bipolar disorder and 18 healthy controls, we examine the relationship between lithium therapy, AVP levels and the cortisol response to the dexamethasone/corticotropin-releasing hormone (dex/CRH) test. These data demonstrate that patients taking lithium have elevated post-dexamethasone AVP levels compared to both healthy controls and patients not on lithium.

Role of heme-oxygenase pathway on vasopressin deficiency during endotoxemic shock-like conditions

The septic shock is characterized by decrease in median arterial pressure; many researchers have been related a deficiency in vasopressin release during the septic shock. Lipopolysaccharide administration is used to induce septic shock model in animals. We investigated the heme-oxygenase (HO) inhibition during the endotoxemic shock-like conditions. The LPS administration induced a significant decrease in MAP (-15.4 +/- 1.2 mmHg at second hour, -25.8 +/- 8.7 mmHg at fourth hour, and -22.3 +/- 8.6 mmHg at sixth hour) with a concomitant increase in heart rate (486.3 +/- 55.0, 531.8 +/- 53.8, and 510.0 +/- 55.3 bpm, respectively), a significant decrease in diuresis (from 1.1 +/- 0.7 to 0.4 +/- 0.3/100g body weight at fourth hour), and a transitory decrease in body temperature (from 37.0 +/- 0.5 to 35.4 +/- 0.8 degrees C at second hour). An increase in plasma arginine vasopressin (AVP) concentration (from 3.2 +/- 0.9 to 19.0 +/- 5.7 pg/mL at the first hour) occurred in these animals and was present for 2 h after LPS administration, returning close to basal levels thereafter and remaining unchanged until the end of the experiment. When LPS was combined with the i.c.v. administration of HO inhibitor, we observed a sustained increase in plasma AVP concentration, attenuation in the drop of MAP, and increase in antidiuresis induced by LPS treatment. These data suggest that central HO pathway may activate a control mechanism that attenuates AVP secretion during endotoxemia and may consequently regulate the MAP and diuretic output.

AVP receptor antagonists as aquaretics: review and assessment of clinical data

The antidiuretic hormone arginine vasopressin (AVP) is primarily responsible for regulating osmotic and volume homeostasis of body fluids, largely through binding to vasopressin type 1A (V(1A)) and type 2 (V2) receptors. Increased AVP secretion leads to decreased free water excretion with resulting water retention, and can cause dilutional hyponatremia. A new class of medications known as AVP receptor antagonists induces free water diuresis without natriuresis or kaliuresis, an effect termed aquaresis. Numerous clinical trials show AVP antagonists to be effective at increasing free water excretion and serum sodium in patients with hyponatremia due to the syndrome of inappropriate antidiuretic hormone secretion or edema-forming states such as congestive heart failure and cirrhosis. This article reviews clinical trial data on the AVP antagonists in late development (lixivaptan, satavaptan, and tolvaptan) and recently approved for marketing (conivaptan).

Hydroxyurea induces vasopressin release and cytokine gene expression in the rat hypothalamus

We previously showed that the cytostatic drug hydroxyurea (HU) activates the hypothalamo-pituitary-adrenal (HPA) axis in intact rats, whereas it is lethal in rats with impaired HPA function. In these animals, HU toxicity is mediated by increased circulating levels of proinflammatory cytokines, whose secretion cannot be counteracted by glucocorticoids, suggesting that HPA activation blunts HU toxicity. Here we investigated the mechanisms through which HU activates the HPA axis, looking at the direct effects of the drug on the isolated hypothalamus. We found that HU significantly increases the release of arginine vasopressin but not that of corticotrophin-releasing hormone in short-term incubation experiments. The levels of arginine vasopressin are also increased in the hypothalamus and systemic circulation 2 h after the in vivo administration of the drug. Furthermore, HU increased significantly the expression of interleukin-6 and, to a lesser extent, interleukin-1beta in the hypothalamus. Interestingly, experiments with HU on primary cultures of rat microglia and astrocytes suggested that the increase in cytokine gene expression observed in hypothalamic explants is not accounted for by glial cells. Since both vasopressin and cytokines can activate the HPA axis, our present findings provide a reasonable explanation of the HPA activation elicited by HU in vivo in the rat.

Vasopressin receptor antagonists: mechanisms of action and potential effects in heart failure

Increased arginine vasopressin (AVP) secretion in heart failure may lead to vasoconstriction, left ventricular remodeling, and water retention-actions that promote afterload, preload, and hyponatremia and thereby cause disease progression. Interfering with AVP-mediated signaling pharmacologically may be beneficial in heart failure. Selective antagonism of the vasopressin 2 (V2) receptor may facilitate a safe diuresis and normalize low serum sodium levels, as demonstrated in preliminary clinical trials. Pure V2 antagonism, however, may stimulate AVP secretion and enhance V1a signaling, while pure V1a receptor antagonism may lead to unwanted V2 stimulation and secondary water retention and volume expansion. Combined V1a and V2 receptor antagonism could potentially prove advantageous as a therapy for heart failure by acting synergistically to facilitate diuresis and improve hemodynamics.

The clinical effects of vasopressin receptor antagonists in heart failure

The neurohormone arginine vasopressin (AVP) is a promising target in the treatment of heart failure because AVP promotes congestion and hyponatremia, each of which is associated with poor outcomes. Diuretics are standard therapy for heart failure, but they have several limitations, including worsening renal function and hyponatremia. Blocking AVP leads to effective aquaresis, improvements in hemodynamics and renal function parameters, weight loss, and normalization of serum sodium, without changes in blood pressure or heart rate. In placebo-controlled trials in the inpatient and outpatient setting, the AVP receptor antagonist tolvaptan reduced body weight and edema and normalized serum sodium in patients with heart failure.

Treating hyponatremia in heart failure

Hyponatremia is common and associated with adverse outcomes in patients with congestive heart failure (CHF). In many patients who have CHF with hyponatremia, plasma arginine vasopressin (AVP) is elevated inappropriately. AVP causes water retention by interacting with V2 receptors in the renal collecting duct, leading to dilutional hyponatremia and increased ventricular preload. AVP also may contribute to pathophysiologic process in CHF by interacting with V(IA) receptors on vascular smooth muscle cells and myocytes. The potential utility of AVP antagonists--V2 antagonists and dual V(IA)/V2 antagonists--in correcting hyponatremia and relieving the congestion and edema associated with CHF is being actively explored. Combined antagonists may offer additional benefit by interfering with excessive V(IA) signaling. Unlike diuretics, which increase urine volume and electrolyte excretion, AVP antagonists of these types produce an aquaresis characterized by an increase in free water clearance concomitant with sparing of electrolytes. Studies in experimental CHF as well as preliminary clinical trials with selective and nonselective V2 antagonists have been encouraging, suggesting that these agents may hold promise for treatment of hyponatremia in CHF.

Amygdalar vasopressin mRNA increases in acute cocaine withdrawal: evidence for opioid receptor modulation

In humans, stress is recognized as a major factor contributing to relapse to drug abuse in abstinent individuals; drugs of abuse themselves or withdrawal from such drugs act as stressors. In the animals, evidence suggests that centrally released arginine vasopressin in both amygdala and hypothalamus plays an important role in stress-related anxiogenic behaviors. The stress responsive hypothalamic-pituitary-adrenal axis is under tonic inhibition via endogenous opioids, and cocaine withdrawal stimulates hypothalamic-pituitary-adrenal activity. The present studies were undertaken to determine whether: (1) 14-day (chronic) "binge" pattern cocaine administration (45 mg/kg/day) or its withdrawal for 3 h (acute), 1 day (subacute) or 10 days (chronic) alters arginine vasopressin mRNA levels in amygdala or hypothalamus; (2) the opioid receptor antagonist naloxone (1mg/kg) alters arginine vasopressin mRNA or hypothalamic-pituitary-adrenal hormonal responses in acute cocaine withdrawal; and (3) there are associated changes of mu opioid receptor or proopiomelanocortin mRNA levels. In amygdala, arginine vasopressin mRNA levels were unchanged after chronic "binge" cocaine, but were increased during acute cocaine withdrawal. Naloxone completely blocked this increase. Neither chronic cocaine nor its acute withdrawal altered amygdalar mu opioid receptor mRNA levels. The increase in amygdalar arginine vasopressin mRNA levels was still observed after subacute withdrawal, but not after chronic withdrawal. Although hypothalamic-pituitary-adrenal tolerance developed with chronic "binge" cocaine, there were modestly elevated plasma adrenocorticotropin hormone levels during acute withdrawal. While naloxone produced modest adrenocorticotropin hormone elevations in cocaine-naïve rats, naloxone failed to elicit an adrenocorticotropin hormone response in cocaine-withdrawn rats. In hypothalamus, neither chronic cocaine nor acute withdrawal altered arginine vasopressin, proopiomelanocortin or mu opioid receptor mRNA levels. These results show that: (1) opioid receptors mediate increased amygdalar arginine vasopressin gene expression during acute cocaine withdrawal, and (2) cocaine withdrawal renders the hypothalamic-pituitary-adrenal axis insensitive to naloxone. Our findings suggest a potential role for amygdalar arginine vasopressin in the aversive consequences of early cocaine withdrawal.

AVP- and OT-neurophysins response to apomorphine and clonidine in major depression

A number of studies have reported abnormalities of neurohypophyseal secretions in major depressive disorder. The purpose of the present study was to test the influence of apomorphine and clonidine injections on plasma vasopressin (AVP)-neurophysins and oxytocin(OT)-neurophysins levels, as direct index of posterior pituitary activation in major depression. Apomorphine and clonidine tests were carried out in 25 medication-free depressive patients and 25 age and gender-matched healthy controls. Blood for neurophysins analysis was drawn by venipuncture at t0, t + 20, t + 40, t + 60 and t + 120. Baseline AVP-neurophysins concentrations were significantly lower in depressives (0.12 +/- 0.14 ng/ml) than in healthy subjects (0.24 +/- 2.15 ng/ml) (p < 0.04). The response to apomorphine test revealed a significant reduced response at 20 (p = 0.01), 40 (p = 0.007) and 60 (p = 0.02) and 120 (p = 0.02)min. Following clonidine test, post hoc tests also revealed a significant decrease at 0 (p = 0.04), 20 (p = 0.01), 40 (p = 0.007) and 60 (p = 0.02) and 120 (p = 0.006)min. Concerning OT-neurophysins, no significant differences were found between depressed and controls in response to clonidine or apomorphine injections. Following clonidine and apomorphine, major depressives exhibited a significantly lower peak GH response than controls. The study supports partially the hypothesis of a reduced vasopressinergic activity in depression. Moreover, we did not find any influence of acute apomorphine or clonidine injections on vasopressin-neurophysin or oxytocin-neurophysin in depressive patients.

Alpha1 adrenoreceptors mediate the stimulatory effects of oestrogen on stress-related hypothalamic-pituitary-adrenal activity in the female rat

Variation in challenge-induced adrenocorticotropin hormone (ACTH) release over the oestrous cycle occurs in response to fluctuations in circulating concentrations of oestrogen and progesterone. However, how these ovarian steroids interact to regulate the principal ACTH cosecretagogues, corticotropin-releasing hormone (CRH) and arginine vasopressin is not understood. Here, we measured median eminence CRH and vasopressin content in intact cycling female rats, and in ovariectomized (OVX) females steroid-replaced in a manner that approximates the relative release patterns of oestrogen and progesterone seen over the oestrous cycle. Intact cycling females showed significantly higher median eminence CRH and vasopressin concentrations during proestrous and oestrous compared to the diestrous phase. In OVX rats, a single 10 micro g injection of oestrogen failed to mimic this increase in median eminence CRH and vasopressin. However, this dose significantly elevated CRH and vasopressin content in OVX rats previously exposed to diestrous concentrations of oestrogen and progesterone. Moreover, oestrogen priming enhanced restraint-induced depletion of CRH and vasopressin from the median eminence, but only against a background of low oestrogen and progesterone replacement. Oestrogen-induced elevations in median eminence vasopressin (but not CRH) content were reduced by peripheral administration of the alpha1 adrenoreceptor antagonist prazosin. Finally, plasma ACTH concentrations following central injection of the alpha1 receptor agonist, phenylephrine, were significantly higher in rats during proestrous compared to diestrous. These results indicate that the stimulatory effect of oestrogen on both the expression and stress-induced release of ACTH cosecretagogues is exerted only against a background of low oestrogen and progesterone levels, and is mediated, in part, via the alpha1 adrenoreceptor.

Mineralocorticoid treatment upregulates the hypothalamic vasopressinergic system of spontaneously hypertensive rats

Mineralocorticoid effects in the brain include the control of cardiovascular functions, induction of salt appetite, interaction with the vasoactive neuropeptides arginine vasopressin (AVP) and angiotensin II and development or aggravation of hypertension. In this regard, mineralocorticoids may play a pathogenic role in rats with a genetic form of hypertension (spontaneously hypertensive rats, SHR). Our objective was to compare the response of the hypothalamic vasopressinergic system to mineralocorticoid administration in SHR and control Wistar-Kyoto (WKY) rats. Sixteen-week-old male SHR showing a systolic blood pressure of 190 +/- 5 mm Hg and normotensive WKY rats (130 +/- 5 mm Hg) were treated subcutaneously with oil vehicle or a single 10-mg dose of deoxycorticosterone acetate (DOCA). After 2 h, rats were sacrificed and brains prepared for immunocytochemistry of Fos and vasopressin V1a receptor (V1aR) and for non-isotopic in situ hybridization of AVP mRNA. In the basal state, SHR demonstrated a higher number of AVP mRNA- and V1aR-immunopositive cells in the magnocellular division of the paraventricular hypothalamic nucleus (PVN) than WKY rats. After DOCA injection, SHR responded with a significant increase in both parameters with respect to vehicle-injected SHR. In WKY rats, DOCA was without effect on AVP mRNA although it increased the number of V1aR-positive cells. Changes in the number of Fos-positive nuclei were measured in the PVN, median preoptic nucleus (MnPO) and organum vasculosum of the lamina terminalis (OVLT), a circumventricular region showing anatomical connections with the PVN. In vehicle-injected rats, the PVN of SHR showed a higher number of Fos-positive nuclei than in WKY rats, whereas after DOCA treatment, a significant increment occurred in the OVLT but not in the PVN or MnPO of the SHR group only. These data suggest that the enhanced response of the vasopressinergic system to mineralocorticoids may contribute to the abnormal blood pressure of SHR.

Expression of the arginine vasopressin gene in response to salt loading in oxytocin gene knockout mice

Accumulating evidence suggests that both oxytocin and arginine vasopressin (AVP) are vital components in the regulation of body fluid balance. However, the physiological role of oxytocin and possible cooperative interactions between oxytocin and AVP in sodium balance remain obscure, even though recent studies using oxytocin knockout (OTKO) mice suggested that oxytocin may contribute to the regulation of salt appetite. In the present study, we examined the effects of salt loading (drinking 2% NaCl for 5 days) on the expression of the AVP gene in the paraventricular (PVN) and supraoptic nuclei (SON) of wild-type, OTKO and heterozygous littermates using in situ hybridization histochemistry. In addition, the effects of salt loading on the expression of the oxytocin gene were also examined in wild-type and heterozygous mice. Under the non salt-loaded condition, the levels of AVP mRNA in the PVN and SON of OTKO mice were significantly decreased compared to those in wild-type mice. Nevertheless, the up-regulation of the expression of the AVP gene in response to salt loading was preserved in OTKO mice. The degree of the up-regulation in OTKO mice tended to be greater compared to those in wild-type mice, suggesting compensatory up-regulation of the expression of the AVP gene in OTKO mice after salt loading. The basal levels of oxytocin mRNA in the PVN and SON of heterozygous mice were significantly lower than those in wild-type mice. Salt loading caused an increase of oxytocin mRNA levels in the PVN and SON of both wild-type and heterozygous mice. The ratios of increase of oxytocin mRNA levels were very similar between wild-type and heterozygous mice, suggesting that the single remaining oxytocin gene in heterozygous mice responds normally to an osmotic cue. Finally, salt loading tended to increase the serum concentration of sodium regardless of genotype, and there were no genotype differences in both the control and salt-loaded groups. These results suggest ways in which oxytocin may play a cooperative role together with AVP in the regulation of sodium balance.

Monoaminergic control of vasopressin and VIP expression in the mouse suprachiasmatic nucleus

We studied the effects of serotonin and noradrenaline on the expression of arginine-vasopressin (AVP) and vasoactive intestinal peptide (VIP) in the suprachiasmatic nucleus (SCN). We used transgenic Tg8 mice knockout for the MAO-A (monoamine oxidase A) gene, which are characterized by increased amounts of serotonin and noradrenaline in brain compared to wild-type mice (C3H). The MAO-A deficiency caused an increase in AVP and VIP expression (determined by immunohistochemistry, enzyme immunoassay, and in situ hybridization) compared to C3H mice. The number of peptidergic neurons was also increased. Inhibiting serotonin or noradrenaline synthesis in Tg8 mice by the administration of parachlorophenylalanine or alpha-methylparatyrosine, respectively, the amounts of AVP, VIP and their mRNAs were decreased, but not the number of peptidergic neurons. This study indicates that serotonin and noradrenaline stimulate AVP and VIP expression, and could participate in the differentiation of the neurochemical phenotype in the mouse SCN.

Alcohol differentially affects c-Fos expression in the supraoptic nucleus of long-sleep and short-sleep mice

Ethanol administration in long-sleep (LS) and short-sleep (SS) mice results in a large number of Fos-IR neurons in the supraoptic nucleus (SON) in LS, and almost no Fos-IR neurons in the same nucleus in SS mice. In contrast, isotonic saline, hypertonic saline, with or without ethanol, resulted in a similar pattern of Fos-IR in both strains. These data indicate a differential effect of ethanol on c-Fos signaling specifically in the SON. Since the LS and SS mice were specifically selected for differential sensitivity to the sedative/hypnotic effects of ethanol, this differential in c-Fos activity may be causally implicated in their differential sensitivity to ethanol.

Time-dependent sensitization of corticotropin-releasing hormone, arginine vasopressin and c-fos immunoreactivity within the mouse brain in response to tumor necrosis factor-alpha

Stressor or cytokine treatments, such as interleukin-1beta, promote time-dependent alterations of hypothalamic-pituitary-adrenal functioning, including increased arginine vasopressin stores within corticotropin-releasing hormone (CRH) terminals in the external zone of the median eminence. Likewise, we have previously shown that the proinflammatory cytokine, tumor necrosis factor-alpha (TNF-alpha), provoked a time-dependent sensitization of neuroendocrine and brain monoamine activity. To further explore the protracted consequences of TNF-alpha, the present investigation determined whether the cytokine sensitized activity of neuroendocrine regulatory brain regions, as assessed by c-fos expression, and had protracted consequences on amygdaloid CRH, as well as hypothalamic corticotropin secretagogues. Indeed, immunoreactivity for arginine vasopressin and corticotropin-releasing hormone, and their colocalization within cell terminals of the median eminence, varied over time following an initial 4.0-microg tumor necrosis factor-alpha treatment, peaking after 7 days and normalizing within 28 days. Within the central amygdala, a sensitization effect was evident as reflected by increased CRH immunoreactivity, but this effect required re-exposure to the cytokine, unlike the median eminence changes that simply evolved with the passage of time. As well, tumor necrosis factor-alpha provoked a marked sensitization of c-fos staining within the paraventricular nucleus of the hypothalamus, supraoptic nucleus and the central amygdala. From these data we suggest that tumor necrosis factor-alpha influences responsivity of stressor-reactive brain regions and has protracted effects on central neuropeptide expression within the hypothalamus and central amygdala, although the time course for the effects vary across brain regions. Evidently, exposure to tumor necrosis factor-alpha may promote neuroplasticity of brain circuits involved in mediating neuroendocrine, sickness or inflammatory responses. It is suggested that such a sensitization may influence the response to immunological and traumatic insults and may thus be relevant to behavioral pathology.

AT1 receptor antagonist telmisartan administered peripherally inhibits central responses to angiotensin II in conscious rats

The effects of systemic treatment with the AT1 receptor antagonist telmisartan on central effects of angiotensin II (Ang II), namely, increase in blood pressure, vasopressin release into the circulation, and drinking response, were investigated in conscious, normotensive rats. The central responses to i.c.v. Ang II (30 ng/kg) were measured at 0.5, 2, 4, and 24 h following acute i.v. or acute and chronic oral telmisartan application. At a dose of 10 mg/kg i.v., the drinking response to i.c.v. Ang II was completely blocked over 4 h, while the pressor response and the release of vasopressin in response to i.c.v. Ang II were blocked by 60 to 80%. The inhibition of the centrally mediated pressor and drinking response to Ang II was sustained over 24 h. The lower doses of telmisartan (0.3 and 1 mg/kg) significantly inhibited the Ang II-induced actions over 4 h. A consistent 24-h inhibition of the central responses to i.c.v. Ang II was obtained after acute and chronic oral treatment with 30 mg/kg telmisartan. Oral treatment with 1 and 3 mg/kg telmisartan produced a slight but inconsistent inhibition of the central actions of Ang II. Telmisartan concentrations measured in the cerebrospinal fluid following 8 days of consecutive daily oral treatment (1-30 mg/kg) ranged from 0.87 +/- 0.27 ng/ml (1 mg/kg/day) to 46.5 +/- 11.6 ng/ml (30 mg/kg/day). Our results demonstrate that, following peripheral administration, the AT1 receptor antagonist telmisartan can penetrate the blood-brain barrier in a dose- and time-dependent manner to inhibit centrally mediated effects of Ang II.

Estrogen and androgen influence hypothalamic AVP and CRF concentrations in fetal and adult sheep

The present study tested the hypothesis that action of sex steroids on the hypothalamus-pituitary-adrenal (HPA) axis is measurable in the hypothalamus. Late-gestation fetal sheep were treated (5 mg/21 days) with either estradiol, androstenedione, or tamoxifen and compared to age-matched control fetuses. Tamoxifen significantly increased hypothalamic corticotropin releasing factor (CRF) and arginine vasopressin (AVP) concentrations, and androstenedione significantly decreased hypothalamic CRF concentration. Adult sheep were treated with estrone (10 mg/21 days), and responded with significant increases in hypothalamic AVP concentration, but not in immunoreactive ACTH concentration or processing within the pituitary. The results demonstrate that the effect of estrogen on the HPA axis is measurable in the hypothalamus, and is therefore not primarily at the anterior pituitary.

Male-female differences in rat hypothalamic-pituitary-adrenal axis responses to nicotine stimulation

Hypothalamic-pituitary-adrenal (HPA) axis responsiveness differs physiologically and pharmacologically between the sexes (sexual diergism). Central nicotinic receptors modulate this endocrine axis. Previous studies have established that nicotine (NIC) stimulates the HPA axis; however, only male animals have been used. We have demonstrated that plasma arginine vasopressin (AVP) and adrenocorticotropic hormone (ACTH) concentrations showed greater responsiveness in male than in female rats pretreated with scopolamine (SCOP), a muscarinic antagonist, followed by physostigmine (PHYSO), an acetylcholinesterase inhibitor. These results suggest that the SCOP + PHYSO effects may have resulted from an indirect nicotinic effect caused by increased synaptic acetylcholine with simultaneous muscarinic antagonism. In the present study, we investigated nicotinic cholinergic influences on HPA axis activity in male and female rats by administering NIC (0, 0.03, 0.1, 0.3, or 0.5 mg/kg) and determining plasma AVP, ACTH, and corticosterone (CORT) responses. Male rats had a significantly greater, dose-related AVP response to NIC than did females. In contrast, female rats had significantly greater, dose-related ACTH and CORT responses to NIC than did males. Hormone responses following NIC were similar to hormone responses following SCOP + PHYSO. These results suggest nicotinic receptors influence the HPA axis differentially in male and female rats.

Slowing the progression of CHF. Drug therapy to correct neurohormonal abnormalities

As the population ages, the number of cases of congestive heart failure (CHF) is expected to climb. Primary care physicians will be increasingly called upon to treat patients with this serious cardiac derangement. In this article, Drs Ward and Anderson discuss the latest approaches to treatment, which are based on the current understanding that CHF results from left ventricular dysfunction, which causes a complex activation of multiple neurohormonal reflexes.

Dose response of arginine vasopressin to the CCK-B agonist pentagastrin

Cholecystokinin (CCK) is a peptide neurotransmitter that modulates hypothalamic-pituitary-adrenal (HPA) axis activity and may be involved in fear or anxiety states. Arginine vasopressin (AVP) also modulates HPA axis activity and may play a role in fear conditioning. Few human studies have examined interactions between CCK and AVP systems. To explore relationships between CCK-B receptor activation, the HPA axis response, and AVP release, a dose-response study using the CCK-B receptor agonist pentagastrin was conducted. Adrenocorticotropin (ACTH) and cortisol results have been previously reported and AVP data is presented here. Thirty-five healthy subjects were randomly assigned to receive placebo, or 0.2, 0.4, 0.6, or 0.8 microg/kg doses of pentagastrin. AVP release appeared to increase with increasing doses of the CCK-B agonist. However, this may have been due to a greater percentage of subjects releasing AVP in the higher dose groups, rather than a direct effect of dose on magnitude of response. AVP and ACTH responses were correlated, but AVP response alone could not account for the magnitude of the ACTH response. AVP release was significantly correlated with anxiety symptom responses. These findings suggest a possible role for the CCK-B receptor in AVP release, which may be at least partially separate from its role in modulation of the HPA axis. Further work is needed to determine whether these are physiologically meaningful interactions and to determine their functional implications.

Acetaldehyde, a metabolite of ethanol, activates the hypothalamic-pituitary-adrenal axis in the rat

Cyanamide is a potent inhibitor of aldehyde dehydrogenase (ALDH: EC 1.2.1.3) used in the treatment of alcoholics. In the presence of ethanol, cyanamide causes an accumulation of acetaldehyde, a highly toxic metabolite of ethanol, with unpleasant side-effects. A similar accumulation is seen in some Oriental people with low ALDH activity. We have investigated the effects of ethanol and cyanamide administration on the activation of the hypothalamic-pituitary-adrenal (HPA) axis using in situ hybridization histochemistry and radioimmunoassay. Ethanol plus cyanamide resulted in a significant increase in corticotrophin-releasing factor and arginine vasopressin mRNA in the paraventricular nucleus, and pro-opiomelanocortin mRNA in the anterior pituitary. Plasma corticosterone concentrations were also significantly elevated following ethanol plus cyanamide administration. The blood concentration of acetaldehyde in the ethanol plus cyanamide group increased significantly. These results suggest that acetaldehyde, induced by blocking ethanol metabolism, is able to activate the HPA axis operating through a central mechanism.

In vitro entrainment of the circadian rhythm of vasopressin-releasing cells in suprachiasmatic nucleus by vasoactive intestinal polypeptide

Mammalian circadian pacemaker is located in suprachiasmatic nuclei (SCN) of the hypothalamus. The pacemaker is entrained by light-dark cycle; the photic information is transmitted primarily via the retino-hypothalamic tract (RHT). The main neurotransmitter of the tract is glutamate. RHT fibers end on the ventrolateral part of the nucleus, where vasoactive intestinal peptide (VIP)-immunopositive neurons are localized. They send their axons into dorsomedial SCN, where most of the vasopressinergic (AVP) neurones are located. The AVP neurons retain the clock-like properties in vitro. Vasopressin release from the cultured neurons shows circadian rhythm peaking in the middle of subjective day. VIP induces phase-shifts of the rhythm, magnitude and direction of the shift depending on timing of the application. VIP applied 6-12 h before the peak of vasopressin rhythm induces advances, application 4-8 h after the peak induces delays. The lowest concentration required to induce the phase-shift is 30 nM, further increase of the concentration does not affect the magnitude of the shift. In contrast, glutamate has no effect on the phase of vasopressin rhythm, although in high concentrations it transiently stimulates vasopressin release. The data indicate that the vasopressinergic cells in the SCN contain circadian oscillators, whose rhythms run mutually synchronized in our cultures. VIP acts directly on the vasopressinergic cells to shift the phase of their pacemakers; glutamate has no such effect presumably because in vivo it acts through the VIP-ergic cells but the neuronal network is altered after the dissociation of the cells.

Estrogen increases arginine-vasopressin V1a receptor mRNA in the preoptic area of young but not of middle-aged female rats

We determined whether estrogen regulates the expression of arginine-vasopressin (AVP) receptor mRNA in the preoptic area (POA) of female rats. By reverse transcription-polymerase chain reaction (PCR), we found that all three types of the AVP receptor mRNA, V1a, V1b and V2, were expressed in the POA, though the amount of PCR products was apparently different among them. In situ hybridization indicated that AVP V1a receptor mRNA was densely expressed in the POA, especially in the anteroventral periventricular nucleus of the POA; in contrast, AVP V1b and V2 receptor mRNAs were not abundant in this area. Finally, we demonstrated by Northern blot that estrogen significantly increased the expression of AVP V1a receptor mRNA in the POA of young ovariectomized rats. However, this regulation by estrogen was lost in middle-aged rats, indicating an age-related impairment in the regulation of AVP V1a receptor mRNA by estrogen in the POA.

Renal electrolyte and fluid handling in the rat following chloroquine and/or ethanol administration

We postulated that chloroquine and/or ethanol affect plasma arginine vasopressin (AVP) concentrations to alter renal function. Therefore, we studied the effects of chloroquine and/or ethanol on plasma AVP concentrations and fluid, urinary Na(+) and K(+) outputs in separate groups of anaesthetized Sprague-Dawley (SD) rats challenged with a continuous jugular infusion of 0.077 M NaCl at 150 microl.min(-1). After a 3-h equilibration period, vehicle, chloroquine (0.06 microg. min(-1)), ethanol (2.4 or 24 microg.min(-1)) or both chloroquine and ethanol were added to the infusate after 1 h (control) for 1 h 20 min (treatment). The animals were switched back to the infusate alone for the final 1 h 40 min recovery periods. Urine flow Na(+) and K(+) excretion rates were determined at 20-min intervals over the subsequent 4-h postequilibration period. Blood was collected from separate groups of animals at the end of treatment period or equivalent time for control animals for measurement of plasma aldosterone and AVP concentrations by radioimmunoassay. Simultaneous chloroquine and ethanol infusion significantly (p < 0.01) increased plasma chloroquine concentrations in an ethanol dose-dependent manner by comparison with animals administered chloroquine alone. Chloroquine infusion alone (0.06 microg.min(-1)) and/or ethanol (2.4 or 24 microg.min(-1)) elevated plasma AVP concentrations from 9.73 +/- 1.64 fmol.l(-1) in control rats to 15.65 +/- 2.49 fmol.l(-1), 17. 39 +/- 4.21 fmol.l(-1), and 33.87 +/- 6.18 fmol.l(-1), respectively. Separate administration of chloroquine or ethanol at low dose rates increased urinary Na(+) excretion rates. We conclude that the impairment of renal electrolyte handling associated with chloroquine administration may be exacerbated by ethanol.

Effects of centrally administered pituitary adenylate cyclase-activating polypeptide on c-fos gene expression and heteronuclear RNA for vasopressin in rat paraventricular and supraoptic nuclei

The effects of intracerebroventricular (i.c.v.) administration of pituitary adenylate cyclase-activating polypeptide (PACAP) on the expression of c-fos gene as well as heteronuclear (hn) RNA for arginine vasopressin (AVP) in paraventricular (PVN) and supraoptic nuclei (SON) of rats were investigated by immunohistochemistry for c-fos protein (Fos) and in situ hybridization histochemistry for c-fos mRNA and AVP hnRNA. The i.c.v. administration of PACAP (200 pmol/rat) caused a marked induction of Fos-like immunoreactivity (LI) in PVN and SON. The nuclear Fos-LI existed in AVP-LI containing cells in the PVN and SON. The expression of the c-fos gene in the PVN and SON was increased in a dose-related manner 30 min after i.c. v. administration of PACAP. PACAP-induced expression of the c-fos gene was significantly reduced by pretreatment with a PACAP receptor antagonist, PACAP-(6-38)-NH2. In addition, Fos-LI and the expression of the c-fos gene were also observed in the periventricular region of the third ventricle after i.c.v. administration of PACAP. The induction of c-fos gene expression in the PVN and SON reached a maximum 30 min after PACAP administration. The expression of c-fos gene in the PVN and SON induced by i.c.v. administration of vasoactive intestinal peptide (200 pmol/rat) was weaker than that induced by PACAP. The hnRNA for AVP in the PVN and SON was significantly increased 30 min after i.c.v. administration of PACAP (200 pmol/rat). Our results suggest that PACAP activates PVN and SON neurons via PACAP receptors and, in parallel, transcription of the AVP gene in the PVN and SON.

Central losartan blocks natriuretic, vasopressin, and pressor responses to central hypertonic NaCl in sheep

This study investigated the effect of intracerebroventricular administration of the angiotensin AT1 receptor antagonist losartan on the natriuresis, pressor effect, and arginine vasopressin (AVP) secretion caused by intracerebroventricular infusion of either ANG II, hypertonic saline, or carbachol. Losartan (1 mg/h) or artificial cerebrospinal fluid (CSF) was infused into the lateral ventricle before, during, and after infusions of either ANG II at 10 microg/h for 1 h, 0.75 mol/l NaCl at 50 microl/min for 20 min, or carbachol at 1.66 microg/min for 15 min. Intracerebroventricular infusions of ANG II, 0.75 mol/l NaCl, or carbachol caused increases in renal Na+ and K+ excretion, arterial pressure, and plasma AVP levels. Increases in arterial pressure, Na+ excretion, and plasma AVP concentration ([AVP]) in response to intracerebroventricular ANG II or intracerebroventricular 0.75 mol/l NaCl were either abolished or attenuated by intracerebroventricular infusion of losartan but not by intracerebroventricular infusion of artificial CSF or intravenous losartan. Intracerebroventricular losartan did not reduce the increase in plasma [AVP] or arterial pressure in response to intracerebroventricular carbachol, but it did attenuate the natriuretic response to intracerebroventricular carbachol. We conclude that an intracerebroventricular dose of losartan (1 mg/h) that inhibits responses to intracerebroventricular ANG II also inhibits vasopressin secretion, natriuresis, and the pressor response to intracerebroventricular hypertonic saline. These results suggest that common neural pathways are involved in the responses induced by intracerebroventricular administration of ANG II and intracerebroventricular hypertonic NaCl. We propose that intracerebroventricular infusion of hypertonic saline activates angiotensinergic pathways in the central nervous system subserving the regulation of fluid and electrolyte balance and arterial pressure in sheep.

Metabolism and action of urodilatin infusion in healthy volunteers

OBJECTIVES

The objective of this investigation was to study both the pharmacokinetics and renal pharmacodynamic properties of intravenously infused urodilatin in human beings.

METHODS

Twelve healthy subjects received a short-term infusion (90 minutes) of urodilatin and placebo with a graded infusion rate (from 7.5 to 15 to 30 ng.kg body weight-1.min-1) in a randomized, double-blind, crossover study design. The renal parameters were evaluated by clearance technique with the use of 51Cr-ethylenediaminetetraacetic acid, 125I-hippuran, and lithium. Urodilatin concentrations were determined by a radioimmunoassay with a urodilatin-specific antibody.

RESULTS

Kinetics were characterized by a high apparent volume of distribution (43.7 +/- 11.2 L), a high total body clearance (5383 +/- 581 ml/min), and a short plasma half-life (5.57 +/- 0.8 minutes). The maximal plasma urodilatin level was 177.2 +/- 25.8 pmol/L. Less than 1% of total infused urodilatin was recovered in urine. Urodilatin significantly increased glomerular filtration rate (urodilatin, 7.0%, versus placebo, -1.9%; p < 0.05), reduced effective renal plasma flow (urodilatin, -17%, versus placebo, -3%; p < 0.01), increased fractional excretion of sodium (urodilatin, 137%, versus placebo, 27%; p < 0.05), and increased urine flow rate (urodilatin, 46%, versus placebo, -15%; p < 0.01). Fractional excretion of lithium did not change. Mean blood pressure decreased and vasoactive hormone levels remained unchanged or increased.

CONCLUSION

The natriuretic and diuretic effects of urodilatin closely followed the profile of urodilatin concentration in plasma. A major part of the synthetic urodilatin was removed from circulation by a route other than filtration through the glomeruli.

Cardiovascular, adrenocorticotropin, and cortisol responses to hypertonic saline in euvolemic sheep are altered by prostaglandin synthase inhibition

Small volume intravenous infusions of hypertonic saline (HTS) increase blood pressure, heart rate, adrenocorticotropic hormone (ACTH), and cortisol by mechanisms that are not fully understood. We hypothesized that HTS infusions increase prostaglandin biosynthesis and that a prostaglandin synthase metabolite is responsible for mediating actions of HTS. We further hypothesized that thromboxane A2 (TxA2) is the specific metabolite responsible for mediating responses to HTS infusion. Adult female sheep (n=8) were chronically instrumented with vascular catheters and infused intravenously with 7.5% saline at a rate of 4 mL x kg(-1) over 5 min with or without pretreatment with the prostaglandin synthase inhibitor flunixin. Blood pressure, ACTH, and cortisol increased in response to HTS, and these responses were prevented by flunixin. Heart rate increased in response to HTS infusion, and flunixin reduced but did not prevent a heart rate response. Hematocrit decreased significantly in response to HTS but only following flunixin treatment. Arginine vasopressin increased but only modestly in response to HTS, and responses were not different following flunixin. Arterial pH, partial pressure of CO2, and partial pressure of O2 did not change. Circulating concentrations of thromboxane B2, a stable metabolite of TxA2 and an index of TxA2 formation, remained low and did not change in response to HTS. We conclude that heart rate, blood pressure, ACTH, and cortisol responses to HTS are mediated at least in part by a product of prostaglandin synthase metabolism. These responses were not due to increases in circulating concentrations of TxA2 but might involve local formation of TxA2 or some other prostaglandin synthase metabolite.

Interaction of opioids and vasopressin in central action of angiotensin II in conscious rabbits

It has been demonstrated that opioids modulate the renin-angiotensin and sympathetic nervous system. To clarify the interaction of central angiotensin II (Ang II) and endogenous opioids, we studied the effects of naloxone, an opioid antagonist, on cardiovascular and sympathetic responses to intracerebroventricular (i.c.v.) Ang II in conscious rabbits. I.c.v. Ang II (20 ng/min) significantly increased mean arterial pressure (MAP), plasma epinephrine, and arginine vasopressin (AVP) levels, with no significant change in renal sympathetic nerve activity (RSNA) or heart rate. Pretreatment with intravenous naloxone (0.1 mg/kg) failed to alter the cardiovascular and neurohormonal responses to i.c.v. Ang II. To eliminate the effect of AVP on cardiovascular and sympathetic responses, [d(CH2)5Thy(Me)]AVP, a vasopressin V1-receptor antagonist, was given intravenously. Pretreatment with intravenous injection of the V1-receptor antagonist (30 micrograms/kg) augmented the maximum increase in RSNA caused by i.c.v. Ang II (8.9 +/- 2.2 vs. 16.2 +/- 0.7%, p < 0.05). Combined pretreatment with naloxone and V1-receptor antagonist further increased MAP and RSNA in response to ICV Ang II (20 +/- 1 vs. 16 +/- 2 mmHg, p < 0.05, and 30.9 +/- 3.7 vs. 16.2 +/- 0.7%, p < 0.01, respectively). These results suggest that opioids and AVP synergistically modulate sympathetic outflow so as to suppress the central pressor action of Ang II in conscious rabbits.

Upregulation of hypothalamic nitric oxide synthase gene expression in streptozotocin-induced diabetic rats

Plasma arginine vasopressin (AVP) is known to be elevated in patients with uncontrolled insulin-dependent diabetes mellitus who have plasma hyperosmolality with hyperglycaemia. Although osmotic stimuli cause an increase in nitric oxide synthase (NOS) activity as well as synthesis of AVP and oxytocin in the paraventricular (PVN) and supraoptic nuclei (SON), it is not known whether NOS activity in the hypothalamus changes in the diabetic patients who have plasma hyperosmolality with hyperglycaemia caused by insulin deficiency. Expression of the neuronal (n) NOS gene in the PVN and SON in streptozotocin (STZ)-induced diabetic rats was investigated by using in situ hybridization histochemistry and NADPH-diaphorase histochemical staining. Four weeks after intraperitoneal (i. p.) administration of STZ, male Wistar rats developed hyperglycaemia and plasma hyperosmolality. The expression of nNOS gene and NADPH-diaphorase staining in the PVN and SON remarkably increased in STZ-induced diabetic rats compared to control rats. Three weeks after administration of STZ, the diabetic rats were subcutaneously treated with insulin for 1 week, which resulted in significant suppression of the induction of nNOS, AVP and oxytocin gene expression in the PVN and SON. Furthermore, the induction of nNOS gene expression in the PVN and SON was suppressed in STZ-induced diabetic rats treated with phlorizin and diet to normalize hyperglycaemia without insulin treatment. These results suggest that upregulation of nNOS gene expression as well as AVP and oxytocin gene expression in the PVN and SON in STZ-induced diabetic rats may be associated with hyperglycaemia and plamsa hyperosmolality.

Differential contribution of angiotensinergic and cholinergic receptors in the hypothalamic paraventricular nucleus to osmotically induced AVP release

We studied the involvement of periventricular and hypothalamic angiotensinergic and cholinergic pathways in osmotically induced arginine vasopressin (AVP) release into the blood. In conscious Wistar rats, i.c.v. injections of 0.2, 0.3 and 0.6 M hyperosmolar saline (5 microl) resulted in concentration-dependent increases in AVP release (5.2 +/- 1.5, 10.6 +/- 2.2 and 18.0 +/- 2.2 pg/ml, respectively, vs. 2.0 +/- 0.1 in controls). The two lower saline concentrations did not affect arterial blood pressure (non-pressure-associated AVP release), whereas 0.6 M saline induced increase in blood pressure (pressure-associated AVP release). In the first set of experiments, periventricular angiotensin AT1, muscarinic or nicotinic receptors were blocked by i.c.v. administration of losartan (10 nmol), atropine (100 nmol) or hexamethonium (100 nmol), respectively, before i.c.v. hyperosmolar saline injections. Losartan significantly reduced the 0.2 M and 0.3 M, but not the 0.6 M, saline-induced increase in AVP release. The 0. 3 M saline-induced AVP release was blocked by atropine and hexamethonium, whereas the 0.6 M saline-induced AVP release was blocked by atropine only. In the second set of experiments, losartan (4 nmol), atropine (200 nmol) or hexamethonium (200 nmol) was injected bilaterally into the paraventricular nucleus before i.c.v. hyperosmolar saline injections. Losartan reduced 0.3 M and potentiated 0.6 M saline-induced AVP release. On the other hand, atropine and hexamethonium significantly reduced both 0.3 and 0.6 M saline-induced AVP release. We conclude that afferents arising from periventricular osmosensitive neurons to the hypothalamic paraventricular nucleus, which are involved in non-pressure-associated osmotically induced AVP release, are both angiotensinergic and cholinergic, whereas those mediating pressure-associated AVP release are cholinergic in nature.

Effect of melatonin on hypoglycemia and metoclopramide-stimulated arginine vasopressin secretion in normal men

The present study was performed in order to establish whether melatonin (MEL) plays a role in the regulation of arginine vasopressin secretion (AVP) in normal human subjects. For this purpose, the effects of an oral administration of 6 or 12 mg MEL on basal and metoclopramide (MCP)- or hypoglycemia-stimulated AVP secretion was tested in 18 normal men. MCP was given at a dose of 20 mg as an intravenous (i.v.) bolus; hypoglycemia was induced with an i.v. bolus injection of 0.15 IU/kg body weight of insulin. In addition, in view of the well-known inhibitory effect of MEL on the growth hormone (GH) response to hypoglycemia, GH levels were measured during the insulin tolerance test (ITT), as an independent index of MEL activity. MEL did not produce any change in AVP secretory patterns in basal conditions or during the MCP test. In contrast, the mean peak AVP response to hypoglycemia was 2.33 times higher than baseline in the control ITT, whereas it was only 1.77 times higher than baseline in the ITT plus MEL tests. Also, the GH response to hypoglycemia was significantly lower in the presence than in the absence of MEL. For both AVP and GH, the inhibitory effect of MEL during ITT was similar, when either 6 or 12 mg MEL was given. These data indicate an involvement of MEL in the control of the AVP response to hypoglycemia, but not of basal and MCP-induced AVP secretion. In addition, the similar effects of MEL on GH and AVP secretions during ITT suggest that similar neuroendocrine mechanisms underlie these hormonal responses to hypoglycemia.

Stimulation of arginine vasopressin secretion by a small increase in blood ionized calcium in normal men

Evidence has been provided for an increase in baseline serum corticotrophin (ACTH) levels in response to a rise in circulating ionized calcium (Cai) levels within the physiological range. In order to establish whether small Cai increments are also able to modify the basal secretion of arginine vasopressin (AVP), we infused calcium gluconate through an intravenous infusion pump in eight healthy male subjects (25-31 years old). Serum Cai, ACTH and AVP concentrations were measured every 10 min over an infusion period lasting 90 min. A significant progressive rise in serum Cai (baseline: 42 +/- 0.9 mg dL-1; 90 min: 47.2 +/- 0.9 mg dL-1, P < 0.001), ACTH (baseline: 30.7 +/- 1.3 pg mL-1; mean peak at 80 min: 37.4 +/- 2.4 pg mL-1, P < 0.01) and AVP levels (baseline: 2.1 +/- 0.6 pg mL-1; mean peak at 80 min: 3.2 +/- 0.5 pg mL-1, P < 0.01) was observed during calcium infusion. Furthermore, a significant positive correlation (r = 0.71; P < 0.001) was observed between ACTH and AVP responses to calcium infusion at 60, 70, 80 and 90 min. These data demonstrate that AVP secretion is stimulated by a slight rapid increase in serum Cai levels even though absolute serum Cai levels remain within the normal range. In addition, the positive correlation between Cai-induced ACTH and AVP increments suggests that AVP plays a releasing role on ACTH secretion during calcium infusion.

C-type natriuretic peptide suppresses arginine-vasopressin secretion from dissociated magnocellular neurons in newborn rat supraoptic nucleus

Central administration of C-type natriuretic peptide (CNP) affects various neuroendocrine systems. In the present study, we examined whether CNP acts directly on arginine-vasopressin (AVP) secretion from rat supraoptic nucleus (SON) neurons, using acute dissociated cell preparations. CNP inhibited the basal secretion of AVP in a dose-dependent manner (10(-11)-10(-6) M). A- type natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) also suppressed the basal secretion of AVP, however, the effects were two-orders of magnitude less potent than CNP. CNP also suppressed All-induced AVP secretion, however, the inhibitory effect of CNP was less than that of ANP or BNP. These findings suggest that CNP inhibits the basal secretion of AVP through natriuretic peptide receptor (NPR)-B and has a role in the body water and electrolyte homeostasis in the central nervous system.

The neurosteroid tetrahydroprogesterone attenuates the endocrine response to stress and exerts glucocorticoid-like effects on vasopressin gene transcription in the rat hypothalamus

The neurosteroid tetrahydroprogesterone (5 alpha-pregnan-3 alpha-ol-20-one, allopregnanolone, THP), has been previously shown to counteract the anxiogenic effects of corticotropin-releasing hormone (CRH) and to interfere with noradrenergic and corticosteroid-mediated regulation of CRH release and gene transcription. Those observations indicated that, besides its sedative and analgesic activity, THP may also affect the neuroendocrine response to stress in a mode resembling that of corticosteroids. To examine this possibility, we compared the ability of THP, its precursor progesterone (P4), and the glucocorticoids dexamethasone (DEX) and corticosterone (CORT) to influence the pituitary-adrenal response to acute emotional stress and the adrenalectomy-induced increase in the gene transcription of the stress-related peptide arginine vasopressin (AVP) and of corticosteroid receptors (MR and GR) in the brain. Pretreatment of rats with a single dose of THP or P4 (50 micrograms/kg) significantly attenuated the elevation of plasma adrenocorticotropin (ACTH) and serum corticosterone after emotional stress; both steroids were, however, less potent than a similar dose of DEX. Administration of 1 mg of THP, CORT, or P4 to adrenalectomized (ADX) rats attenuated the increase in AVP mRNA levels in the ventromedial subdivision of the hypothalamic paraventricular nucleus (PVN), as compared with vehicle-treated ADX rats. However, whereas CORT and P4 influenced the ADX-induced increase in the transcription of both types of corticosteroid receptors in the hippocampus, these were unaffected by THP. In contrast to the glucocorticoids, THP and P4 failed to decrease plasma ACTH levels in rats deprived of endogenous steroids. These results demonstrate that the neurosteroid THP and its precursor P4 resemble glucocorticoids in their suppression of the pituitary-adrenal response to emotional stress; however, THP influences the transcription of glucocorticoid-responsive genes in brain structures involved in the regulation of the hypothalamo-pituitary-adrenal system in a fashion that is quite distinct from that obtained with glucocorticoids.

Interleukin-1 beta-induced effects on plasma oxytocin and arginine vasopressin: role of adrenal steroids and route of administration

The effects of cytokines in stimulating neurohypophysial hormone release have not been well characterized. In the present study, we have investigated the effect of intraperitoneal injection of recombinant human interleukin (IL)-1 beta on oxytocin release in sham-operated controls, adrenalectomized (ADX) rats and ADX rats given either low or high doses of the synthesis glucocorticoid dexamethasone. In a second study, we determined the effect of central injection of IL-1 beta on both oxytocin and arginine vasopressin (AVP) release in sham-operated and ADX rats. We were unable to demonstrate an increase in plasma oxytocin in intact rats in response to intraperitoneal injection of IL-1 beta. In contrast, we found a substantial and sustained increase in plasma oxytocin concentrations in ADX rats. This stimulation was abolished by treatment with dexamethasone at both the low and high doses. Following central injection of IL-1 beta, we were unable to demonstrate any increase in either oxytocin or AVP, despite the ability of this dose of cytokine to stimulate the hypothalamo-pituitary-adrenal axis, as evidenced by increased circulating corticosterone. It appears that circulating glucocorticoids may exert a tonic inhibitory effect on the release of oxytocin in response to peripheral stimulation by IL-1 beta.

Lithium induced polyuria and renal vasopressin receptor density

BACKGROUND

Lithium, a drug frequently used for treatment of affective disorders, is known to cause a vasopressin-resistant state, leading to polyuria and polydipsia. It has been suggested that lithium interacts with the renal V2-vasopressin receptor. Detailed studies on the influence of lithium on the AVP receptor, however, have so far been difficult due to the lack of a suitable radioligand with high specific activity and high affinity.

METHODS

Using 125I-[8-(p-(OH)-phenylpropionyl)]- LVP, we studied the effects of lithium on V2-vasopressin receptors in male Sprague-Dawley rats and LLC-PK1 cells. Rats, having free access to water, were orally treated with 10 mg lithium/100 mg b.w./day or placebo for 10 days. Scatchard analysis was performed using membranes prepared from homogenized renal papillae.

RESULTS

Lithium caused significant polyuria and an impaired renal concentration capacity after water deprivation. Binding studies showed no effect of lithium on binding affinity KD (0.98 +/- 0.21 nmol/l vs. 0.86 +/- 0.15 nmol/l (Li) (n.s.). Receptor density, however, significantly decreased from 130 +/- 12.3 nmol/kg protein in controls (n = 8) to 101.7 +/- 13.4 nmol/kg protein (n = 8), (P < 0.05). Plasma osmotically and AVP were not significantly altered by lithium treatment. Vasopressin receptor density on LLC-PK1-cells, a pig renal cell line, was not changed by preincubation with lithium (312 +/- 22 nmol/kg vs. 329 +/- 25 nmol/kg (Li) (n = 6, n.s.).

CONCLUSIONS

The decrease of AVP-receptor density in vivo might be related to vasopressin resistance, either primary, or secondary to other factors, e.g. actual water transport.

Arginine vasopressin and osmolality in the elderly

OBJECTIVES

To evaluate the influence of age on plasma arginine vasopressin (AVP) concentrations and the relationship between plasma AVP and serum osmolality in younger and older subjects, and in the elderly, to assess the effect of gender on plasma AVP concentration and to determine the impact of prostaglandin blockade on renal responsiveness to AVP.

DESIGN

Cross-sectional study; randomized, double-blind, crossover, placebo-controlled study.

SETTING

The Renal Laboratory, Royal North Shore Hospital (younger adults) and Clinical Room, St Vincents Hospital (elderly subjects).

PARTICIPANTS

45 younger adults (35 +/- 9 years), and 41 elderly subjects (29 males, 12 females; 78 +/- 3 years). All subjects were healthy and non-institutionalized. The elderly subjects were screened to exclude significant pathology (clinical assessment, multiple investigations).

INTERVENTION

Blood samples were drawn from all younger and elderly subjects. The elderly subjects were randomly allocated indomethacin or placebo for 1 month. Following a 1 to 2-week washout, the alternative was administered for a further 1 month.

MAIN OUTCOME MEASURES

Plasma AVP and serum osmolality and plasma AVP, serum, and urine osmolality at baseline were measured on indomethacin and placebo.

RESULTS

In the elderly subjects, baseline plasma AVP concentration was significantly higher than in the younger subjects studied (4.7 +/- 0.7 vs 2.1 +/- 0.2 pg/mL respectively; P = 0.0003). Plasma AVP was strongly correlated with serum osmolality in the younger subjects (r = 0.76, P = 0.0001) but not in the elderly cohort (r = -0.18, P = 0.26). No difference was found between the sexes in plasma AVP (P = 0.89), and indomethacin treatment did not alter the plasma AVP/urine osmolality ratio (P = 0.85) in the elderly subjects. In addition, changes in plasma AVP with indomethacin therapy did not correlate with changes in serum osmolality (r = 0.16, P = 0.09).

CONCLUSIONS

Aging is accompanied by an increase in plasma AVP concentrations. In healthy, elderly subjects, plasma AVP is not dependent on serum osmolality and is not influenced by gender. Indomethacin has no effect on the renal responsiveness to plasma AVP.

[Hemodynamic changes in waking rats with acute streptozotocin diabetes after administration of the combined V2/V1 vasopressin antagonist]

The hemodynamic effect of combined V2/V1 arginine vasopressin (AVP) antagonist in conscious rats with acute 24 hour streptozotocin (STZ)--induced diabetes was studied using the microsphere technique. The rats were made diabetic with a single intravenous injection of STZ (60 mg/kg). One day after STZ administration the hemodynamic parameters in the experimental animals were measured before and 10 minutes after AVP antagonist injection (50 mg/kg, i.v.). The hemodynamic alterations observed post-antagonist included: 1) an increase in the total peripheral resistance (1.84 +/- 0.15 vs. 1.31 +/- 0.12 mm Hg/ml/min per 100 g before antagonist administration, p < 0.05), 2) a decrease in the cardiac index (49.0 +/- 3.1 vs. 68.7 +/- 5.2 ml/min/100 g before antagonist administration, p < 0.05) and stroke volume (0.40 +/- 0.03 vs. 0.57 +/- 0.06 ml before antagonist administration, p < 0.05), 3) a significant (p < 0.05) decrease in the blood flow to the skin, skeletal muscle, stomach, small intestine and kidneys. The mean arterial pressure and heart rate remained unchangeable post-antagonist. These data suggest that AVP is responsible, at least in part, for prominent hemodynamic alterations observed in conscious rats with 24 hour STZ-induced diabetes.