Hypophysiotrophic neurons are capable of altering the ratio of co-packaged neurohormones.

Neuronal dense-core vesicles provide a mechanism whereby peptide messengers are secreted in discrete quanta. Here we report on the capacity of rat hypophysiotrophic corticotropin releasing factor-41 neurons to alter the peptide content as well as the size of dense-core vesicles after removal of glucocorticoid negative feedback by adrenalectomy. We demonstrate, using quantitative immunoelectron microscopy, that long-term adrenalectomy induces a progressive increase in the ratio of vasopressin to corticotropin releasing factor-41-immunoreactive sites in the dense-core vesicle compartment. The intravesicular concentration of vasopressin appeared to be the variable parameter while that of the corticotropin releasing factor-41 remained stable at all survival times after adrenalectomy. Moreover, observations for up to 5 weeks indicate that adrenalectomy results in a progressive increase in the mean volume of dense-core vesicles to about three times normal. These results suggest that the quantal size and the composition of dense-core vesicles are subject to long-term modulation. The capacity of corticotropin releasing factor-41 neurons to alter dense-core vesicles could enhance or diminish the efficacy of the hypothalamohypophyseal communication underlying physiological adaptation to stress, as well as pathological changes.     

The CRF1 receptor antagonist antalarmin reduces volitional ethanol consumption in isolation-reared fawn-hooded rats

Corticotropin releasing factor is a neuropeptide associated with the integration of physiological and behavioural responses to stress. More recently, corticotropin releasing factor has been implicated in the actions of abused drugs, including ethanol. Moreover, previous studies have demonstrated that the non-selective corticotropin releasing factor receptor antagonist, alpha-helical corticotropin releasing factor(9-41), can diminish some of the behavioural effects associated with ethanol withdrawal, whilst the selective corticotropin releasing factor(1) receptor antagonist CP-154,526 has been beneficial in decreasing stress-induced relapse into alcohol-seeking behaviour. However, as yet the ability of selective corticotropin releasing factor compounds to modulate volitional ethanol consumption has not been investigated. For these reasons the present study aims to examine the effects of antalarmin, a selective, centrally acting corticotropin releasing factor(1) receptor antagonist, on both the initiation and maintenance of ethanol consumption in isolation-reared Fawn-Hooded rats. Here we demonstrate that whilst both antalarmin and diazepam can decrease the acquisition of an ethanol-preferring phenotype by Fawn-Hooded rats, only antalarmin can alter established, volitional ethanol consumption. This ability of antalarmin to reduce established ethanol consumption is apparently unrelated to changes in ingestive behaviour, or a generalised anxiolytic action. For these reasons, such drugs may provide a new therapeutic approach for the treatment of alcoholism; however, this requires further investigation.     

The role of neuropeptides in learning and memory: Possible mechanisms

Endogenous neuropeptides such as vasopressin, adrenocorticotropin and opioids have significant effects on learning and memory. However, because of the complexity of behaviour, that is defined as ‘learning’ and ‘memory’ and, because of the limitation of current knowledge, it has been difficult to interpret these behavioural data, especially via neural mechanisms. The application of modern experimental techniques including molecular biology such as cloning and electrophysiology, such as patch-clamp, has had a significant impact upon the concepts about drugs, including neuropeptides action sites. This allows us to try to interpret some behavioural consequences influenced by neuropeptides. The data on effects of some neuropeptides on behaviours and their possible mechanisms are reviewed. Whatever the mechanisms, vasopressin, adrenocorticotropic hormone and endogenous opioids seem to have important effects upon learning and memory and these open up the possibility that drugs enhance cognitive functions or treat dementia via alteration of functions of neuropeptides. Some criteria are proposed for evaluating the validity of behavioural tests for neuropeptides.     

Why does chloroquine impair renal function?: Chloroquine may modulate the renal tubular response to vasopressin either directly by inhibiting cyclic AMP generation,or indirectly via nitric oxide

Chloroquine is one of the antimalaria drugs, also used to treat rheumatoid arthritis and systemic lupus erythematosus (SLE). Although well tolerated in most individuals, it was suggested that chloroquine can exert a profound influence on renal function, especially in individuals with compromised body fluid status. However, epidemiological studies are still lacking. The renal actions of chloroquine are further exacerbated by co-administration of other commonly used drugs such as paracetamol. The following discussion will focus on the evidence that chloroquine is a stimulator of nitric oxide (NO), which mediates many of its renal actions (diuresis, natriuresis and an increase in both glomerular filtration rate (GFR) and plasma vasopressin). Chloroquine appears to modulate the renal tubular response to vasopressin either by directly inhibiting cAMP generation or indirectly via NO.     

Vasopressin and inflammation

At least three vasopressinergic brain systems are involved in inflammatory reaction. The first one is VP neurons of the bed nucleus of stria terminalis, projecting to antipyretic center in the preoptic forebrain region. The second system is neurons of the parvocellular subnucleus of the hypothalmic paraventricular nucleus. VP from these neurons reaches portal blood through the external zone of the median eminence. VP potentiates the effect of corticotropin releasing hormone on ACTH cells in the anterior pituitary. Synergetic modulation of pituitary-adrenal axis by these neurohormones maintains synthesis and release of glucocorticosteroids. The latter plays crucial role as endogenous immunosuppresants. The third VP system is magnocellular hypothalamic neurons that release vasopressin into general circulation. Systemic VP is capable of compensating the water lost caused by symptoms of inflammation. The review is devoted to analysis of current information concerning physiology and interactions between these systems during acute and chronic inflammation. The special reference has been made on the magnocellular neurons and the role of circulating vasopressin in the renal function regulation.     

Analysis of the actions of angiotensin on the central nervous system of conscious dogs

Angiotensin II (ANG II) acts on the brain to elevate blood pressure (BP), stimulate drinking, increase the secretion of vasopressin and corticotropin (ACTH), and inhibit the secretion of renin. The present studies were designed to evaluate the possible physiological significance of these effects. The experiments were performed in conscious dogs with small catheters chronically implanted in both carotid and both vertebral arteries. ANG II was infused into both carotid or both vertebral arteries in doses of 0.1, 0.33, 1.0, and 2.5 ng.kg-1.min-1. Intravertebral ANG II produced dose-related increases in BP that were generally accompanied by increases in heart rate. Intracarotid angiotensin also increased BP but did not change heart rate. Intracarotid ANG II stimulated drinking and, at the highest dose only, increased the secretion of vasopressin, ACTH, and corticosteroids. Intravertebral and intracarotid ANG II suppressed plasma renin activity (PRA). In a parallel series of experiments, the effects of intravenous ANG II, in doses of 2, 5, 10, and 20 ng.kg-1.min-1, were studied. These infusions produced dose-related increases in BP and water intake and suppressed PRA. Only the highest dose of ANG II increased vasopressin or corticosteroid secretion. Analysis of these results in terms of calculated or measured changes in plasma ANG II concentration indicate that the central cardiovascular and dipsogenic actions of angiotensin, as well as the suppression of PRA, can be elicited by concentrations of the peptide that are within the physiological range. On the other hand high, probably supraphysiological, levels of ANG II are required to increase vasopressin or ACTH secretion.     

Regulation of the hypothalamo-pituitary-adrenal axis during stress: feedback,facilitation and feeding

Stressors stimulate the release of corticotropin-releasing factor and/or vasopressin from the hypothalamic paraventricular nuclei causing secretion of adrenocorticotropin from the pituitary and corticosteroids from the adrenal cortex. Corticosteroids inhibit activity in the adrenocortical system by association with high affinity, type I and lower affinity type II corticosteroid receptors in brain. Despite the potent inhibitory effects of exogenously infused corticosteroids on basal and stress-induced adrenocorticotropin, sustained or repeated stress causes facilitated responses to novel stressors. Feedback and facilitation of stress responses are observed during the trough of the basal circadian rhythm but not at the peak. We discuss evidence for the hypothesis that the circadian rhythm in energy acquisition determines the rhythms in stress responsiveness and suggest that the adrenocortical system is embedded in a larger hypothalamic neural network that regulates energy balance.     

Opioid synapses on vasopressin neurons in the paraventricular and supraoptic nuclei of juvenile monkeys.

Opioid peptide- as well as vasopressin-containing neurons synapse on gonadotropin releasing hormone neurons in juvenile macaques. In this study we performed double-label immunostaining for opioid and vasopressin neurons in the paraventricular and supraoptic nuclei in order to assess their interrelationships. Neuroendocrine neurons in the hypothalamus were prelabeled by microinjection of electron-dense retrograde tracer into the median eminence, and were easily identified in frontal Vibratome sections. Sections through the paraventricular and supraoptic nuclei were immunostained for vasopressin with the peroxidase-antiperoxidase technique, and for opioids using the indirect immunogold method. By light microscopy, opioid-immunoreactive inputs appeared to innervate an average of 39% of the vasopressin neurons in the paraventricular nucleus and 33% in the supraoptic nucleus, and were more prevalent anteriorly. Clusters of opioid afferents formed cup-like calices around major processes of many vasopressin neurons, especially in the paraventricular nucleus. Electron microscopy revealed that these groups of opioid axon terminals made frequent symmetrical and fewer asymmetrical synapses on both neuroendocrine and non-neuroendocrine vasopressinergic cell bodies and dendrites. Our study did not reveal vasopressin-opioid synapses in these hypothalamic nuclei, but this does not preclude the possibility of their existence elsewhere. These results indicate that opioid afferents modulate vasopressin neuronal activity in the monkey paraventricular and supraoptic nuclei. Previous results have suggested that corticotropin releasing hormone acts via vasopressinergic neurons to stimulate opioid neuronal activity and to inhibit gonadotropin releasing hormone release. Taken together, the data suggest that stressful stimuli could initiate a series of neuropeptidergic interactions which ultimately alter pulsatile gonadotropin releasing hormone secretion and thus gonadotropin secretion in primates.     

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.     

Calcium flow-independent actions of calcium channel blockers in toad urinary bladder

A role for transmembrane calcium movement in vasopressin stimulation of its target cell has been postulated based on studies with calcium entry blockers such as verapamil. We examined the effect of three sets of structurally different calcium blockers--D600 (an analogue of verapamil), diltiazem, and nifedipine--on water flow in toad bladder. D600 (200 microM), diltiazem (200 microM), and nifedipine (60 microM) inhibited vasopressin-induced water flow but enhanced adenosine 3',5'-cyclic monophosphate (cAMP)-induced water flow, suggesting that the drugs inhibit cAMP generation in response to vasopressin but enhance the response to exogenous cAMP by inhibiting phosphodiesterase activity. In the case of vasopressin stimulation, inhibition of cAMP generation appears to be the overriding effect. This was confirmed by measurements of cAMP content and the protein kinase ratio (-cAMP/+cAMP), which were significantly lower in bladders receiving both D600 and vasopressin than in those receiving vasopressin alone. Furthermore the drugs inhibited activation of adenylate cyclase by vasopressin in cell homogenates and inhibited phosphodiesterase in both homogenates and membrane-free supernatants. Thus these "calcium channel blockers" can directly alter cAMP metabolism in settings where movement of calcium should be irrelevant. The close correlation between the biochemical and transport effects of these agents suggests that their effect on water flow may occur by a direct effect on cellular enzymes or the membranes in which they reside and not by altering local calcium concentrations.     

Immunocytochemical detection of corticotropin-releasing factor: multiple cross-reactions of a widely used carboxy-terminally directed corticotropin-releasing factor antiserum (code rC70) in rat hypothalamus

Forty-one-residue corticotropin-releasing factor is a physiologically significant mediator of the hypothalamic control of corticotropin secretion by the anterior pituitary gland. This releasing hormone is produced by parvicellular neurons in the hypothalamic paraventricular nucleus that project to the external zone of the median eminence. Recent immunocytochemical evidence based on work with a rabbit antiserum against rat corticotropin-releasing factor (code rC70) suggests that about half of the parvicellular corticotropin-releasing factor-containing neurons in the hypothalamic paraventricular nucleus synthesize vasopressin, another potent corticotropin secretagogue, while the rest of the cells do not. If this is indeed the case, the neurohumoral control of corticotropin release may be mediated via distinct hypothalamic effector pathways utilizing releasing hormone cocktails of varying composition. In the present study we have examined the specificity of various antisera against rat corticotropin-releasing factor in immunocytochemical staining. Male Wistar rats pretreated with colchicine were used throughout. The brain was fixed by perfusion with a Zamboni type fixative solution. Vibratome sections of the hypothalamus were immunostained with three different primary antisera (codes rC70, rCRF-3, oCRF-N) using the peroxidase-antiperoxidase or avidin-biotin complex methods. All three antisera stained cell groups previously described to be immunopositive for corticotropin-releasing factor. Most notably, however, rC70 labelled a significant number of additional cells, most readily identified in the arcuate and suprachiasmatic nuclei, as well as in the dorsolateral hypothalamic area caudal to the paraventricular nucleus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Histamine and the hypothalamus

The chemical tools that could be used to examine the function of histamine in the brain are considered together with the evidence linking histamine specifically with the hypothalamus. The distribution of histamine and the enzymes responsible for its synthesis and metabolism is consistent with there being both mast cells and histaminergic nerve terminals within the hypothalamus. Iontophoresis, mepyramine binding and histamine-stimulated adenylate cyclase studies suggest that both histamine H1- and H2- receptors are present in the hypothalamus. In addition, intracerebroventricularly injected histamine receptor agonists and antagonists affect many functions associated with the hypothalamus such as cardiovascular control, food intake, body temperature control, and pituitary hormones whose release is mediated via the hypothalamus, such as corticotropin, growth hormone, thyroid stimulating hormone, prolactin, gonadotropins and vasopressin. However, only in the case of thyroliberin release, prolactin release, body fluid control and blood pressure control is there evidence yet that such effects are mediated via histamine receptors actually in the hypothalamus. The effects of enzyme inhibitors suggest endogenous histamine may be involved in the physiological control of thyroid stimulating hormone, growth hormone and blood pressure, and the effects of receptor antagonists support a role for endogenous histamine in prolactin control. Otherwise, there is little evidence for a physiological role for endogenous, as against exogenous, histamine whether it be from histaminergic terminals or mast cells. In addition, few studies have tried to distinguish possible effects on presynaptic receptors, postsynaptic receptors, hypothalamic blood vessels or the hypophyseal portal blood vessels. It is concluded that although there is good evidence now linking histamine and the hypothalamus more specific studies are required, for instance using microinjection or in vitro techniques and the more specific chemical tools now available, to enable a clearer understanding of the physiological role of histamine in the hypothalamus.     

Genetic models of vasopressin deficiency

Animal models of genetic hormone deficiency are useful as models for physiological studies of hormone deficiency and hormone action. Structure—function studies of the specific underlying gene defect may help in understanding mechanisms regulating gene expression and secretion of the peptide product. Spontaneous genetic models of vasopressin deficiency, such as the Brattleboro rat and human familial diabetes insipidus, have facilitated many studies of vasopressin. However, the Brattleboro rat may not be an ideal model of genetic vasopressin deficiency and therefore could be less useful for studies of the central nervous system or as a background strain for the introduction of new vasopressin gene constructs. The human model is appropriately limited by the constraints of human studies, so that engineered animal models of specific diseases, such as familial neurohypophysial diabetes insipidus, are required. The recent development of a vasopressin-null mouse may provide insights into the various roles of vasopressin in the stress response, cardiovascular regulation and behaviour. Additionally, animals with a complete genetic deficiency of vasopressin can serve as a background strain for introduction of novel vasopressin gene constructs to enable sophisticated studies of the regulation of vasopressin expression and the intracellular processes required for appropriate secretion of vasopressin peptide. As advanced techniques of genetic manipulation become more reliable, conditional expression of vasopressin, regulated by time or body site will permit even more detailed studies in this field.     

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 (45mg/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.     

Evidence for existence of cortical androgen-stimulating hormone.

An animal model using dexamethosone-suppressed, castrated dogs was developed to test the hypothesis that a pituitary hormone other than ACTH modulates adrenal androgen (AA) secretion. Plasma samples were obtained every 15 min during infusions of saline, synthetic alpha 1-24 corticotropin, porcine 1-39 corticotropin (ACTH), or bovine pituitary gland extract (PE) in a wide range of doses. Androstenedione (A), dehydroepiandrosterone (DHA), and cortisol (F) were quantified by radioimmunoassay. When the ratio of AA levels was related to those of F, in order to correct for ACTH content in the PE, the slopes of the dose-response curves for corticotropin and PE were different at the 0.01 level. For A the dose-response slope for the PE was 0.18 +/- 0.5 SE, whereas that of ACTH was 0.02 +/- 0.01. For the DHA response the slopes were 0.17 +/- 0.04 for the PE and 0.04 +/- 0.03 for ACTH. Related studies showed no increase in AA levels in response to luteinizing hormone-releasing hormone, bovine growth hormone (GH), bovine prolactin, ovine thyroid-stimulating hormone (TSH), or synthetic aqueous arginine vasopressin (AVP). We conclude that a pituitary factor other than ACTH, prolactin, GH, luteinizing hormone, follicle-stimulating hormone, TSH, or AVP may be responsible for the observed increase in AA concentrations.     

Immunocytochemical and in situ hybridization detection of hypothalamic neuropeptides from postmortem unfixed rat brains.

The effects of postmortem delay on neuropeptide-containing perikarya was studied in the paraventricular nucleus (PVN) of the rat hypothalamus. Serial sections from brains kept in the skull after death for 6 h and immunocytochemically processed for oxytocin (OT), vasopressin (AVP) and corticotropin releasing factor (CRF) or hybridized in situ for CRF resulted in the well preserved phenotypic expression and stability of mRNA of the aforementioned neuropeptides. Furthermore in most cases, AVP and CRF expression was discernibly enhanced relative to prefixed immunopositive tissue. Results of this study suggest that postmortem variables do not significantly alter the neurochemical coding of magnocellular or parvocellular neurosecretory systems, and support the view that rat and human brain topography can be investigated from tissue left in situ after death for a relatively long period of time.     

Preclinical Evidence for a Role of Glutamatergic Systems in Opioid Tolerance and Dependence

Opioid tolerance and physical dependence are undesirable consequences of chronic opioid use or misuse. Evidence from rodents, using a variety of modes of drug coadministration, reveals that drugs with glutamatergic antagonist activity at the competitive, noncompetitive, or glycine binding sites of the NMDA receptor complex or inhibitors of certain forms of nitric oxide synthase (NOS) can attenuate the development of morphine tolerance and in some cases reverse established tolerance or dependence. Some of these drugs modulate tolerance and dependence without affecting morphine's analgesic effects, suggesting that they prevent neuronal plasticity associated with adaptive changes mediated by the NMDA/NO cascade. Drugs that have a favorable preclinical safety margin are providing leads for new drugs for clinical evaluation.     

The effects of adrenalectomy, corticotropin releasing factor and vasopressin on the sympathetic firing rate of nerves to interscapular brown adipose tissue in the Zucker rat

The firing rate of the sympathetic efferent nerves to interscapular brown adipose tissue (IBAT) is lower in the obese rat compared with the lean rat. The present experiments show that adrenalectomy has no effect on nerve firing rate in the lean rat and a small but statistically nonsignificant effect in the obese rat. Injection of corticotropin releasing factor (CRF) into the IIIrd ventricle produced a dose dependent increase in the firing rate of the sympathetic nerves to interscapular brown adipose tissue (IBAT) in both lean and obese rats. The basal (unstimulated) level of firing was lower in the obese rat compared with the lean rat and remained significantly below lean values at each dose. The minimum dose of CRF to see an effect (125 ng) and the dose at which maximum effect on nerve firing rate was observed (500 ng) was similar in both genotypes. Injection of adrenocorticotropic hormone (ACTH) had no effect on nerve firing rate to IBAT. Central administration of vasopressin produced a significant increase in sympathetic firing rate to IBAT in both lean and obese rats. The temperature of IBAT was also significantly increased with vasopressin and the duration of the response was longer compared with CRF, but the minimum dose to see an effect was higher (2.5 micrograms). The response to vasopressin was greater in the obese rat compared with the lean rat but the maximum firing rate did not achieve levels observed in lean rats. Chronic infusion of CRF into the IIIrd ventricle of obese rats resulted in a reduction of food intake and body weight gain but IBAT mitochondrial GDP binding was unaltered by the treatment. These data are consistent with the hypothesis that the defect in the obese Zucker rat may be due to a glucocorticoid inhibition of CRF and/or vasopressin action in the CNS.     

The influence of salt loading on vasopressin gene expression in magno- and parvocellular hypothalamic neurons: an immunocytochemical and in situ hybridization analysis

Arginine vasopressin peptide and messenger RNA expression were examined at the cellular level in the magnocellular and parvocellular neurons in the rat paraventricular nucleus after dehydration and rehydration, employing immunocytochemistry and in situ hybridization histochemistry on the same tissue sections. Most magnocellular vasopressinergic neurons of control animals expressed both vasopressin-like immunoreactivity and messenger RNA. However, neurons negative for vasopressin-like immunoreactivity but expressing messenger RNA were also detected, and their number increased during dehydration. In contrast, almost all of the parvocellular vasopressinergic neurons of dehydrated animals expressed vasopressin messenger RNA alone, with continued increase in their number after rehydration, despite return of the number of magnocellular vasopressinergic neurons to the control level. Vasopressin messenger RNA and corticotropin releasing factor-like immunoreactivity were co-localized in the same parvocellular neurons, and vasopressin-immunoreactive nerve terminals were detected in the external zone of the median eminence. These findings suggest that magno- and parvocellular vasopressinergic neurons are differentially activated during dehydration/rehydration. Osmotic stimuli activate all magnocellular vasopressinergic neurons, but the effect is not simultaneous in all of these neurons. Parvocellular vasopressinergic neurons are also activated by the stress of dehydration which effect appears to last longer than in the magnocellular system.     

Urinary excretion of angiotensin I, II, arginine vasopressin and oxytocin in patients with anaphylactoid reactions

Human urine samples, purified on octadecasilyl-silica cartridges, contained immunoreactive angiotensin I, II, arginine vasopressin and oxytocin. The daily excretion of these peptides in healthy volunteers was 190.00 +/- 38.43 (n = 12), 17.48 +/- 3.09 (n = 12), 63.43 +/- 14.84 (n = 8) and 13.52 +/- 1.42 (n = 7) pmol/24 hr, respectively (mean +/- s.e.m.). Patients with a history of anaphylactoid reactions to drugs or food additives showed clinical symptoms such as urticaria, flush, nausea, dizziness and hypotension after oral provocation with cyanocobalamine, propyphenazone, acetylsalicylic acid and sodium benzoate. In five of the seven patients, angiotensin I and II were increased several fold in the urine fractions after symptoms were reported. The average increase in the urine concentration of both peptides was fourfold and 5.5-fold. In three out of five patients, the mean excretion of arginine vasopressin and oxytocin immunoreactive material was also elevated by a factor of 5.7 and 4.4, respectively. Oral provocation with a placebo failed to elicit anaphylactoid symptoms or an increase in the urine levels of angiotensin I or angiotensin II. Angiotensin I and angiotensin II-like immunoreactivity could be characterized on HPLC as Ile5-angiotensin I, Ile5-angiotensin II and angiotensin II metabolites. HPLC characterization of immunoreactive arginine vasopressin and oxytocin in two different gradient systems showed retention times different than the retention times of the corresponding synthetic standard peptides indicating that both peptides are not authentic AVP and OXT. These results suggest that angiotensin I and angiotensin II may be involved in the clinical events observed during some forms of anaphylactoid reactions.