The role of endogenous atrial natriuretic peptide in resting and stress-induced release of corticotropin, prolactin, growth hormone, and thyroid-stimulating hormone

Effects of immobilizations stress with or without water immersion on the expression of atrial natriuretic peptide in the hearts of two rat strains

Atrial natriuretic peptide (ANP) is produced and released by mammalian cardiomyocytes and induces natriuresis, diuresis, and lowering of blood pressure. The present study examined localization of ANP and a possible role of the hypothalamic-pituitary-adrenal axis (HPA) activity on the expression of proANP gene in the heart. The Sprague Dawley (SD) and Lewis (LE) rat strains were used. The animals were exposed to the two types of stress: immobilization and immobilization combined with water immersion for 1 hour. Localization of ANP was detected by immunohistochemistry and expression of the proANP mRNA by real-time qPCR in all heart compartments of control and stressed animals after 1 and 3 hours after stress termination (IS1, IS3, ICS1, and ICS3). Relatively high density of ANP-immunoreactivity was observed in both atria of both rat strains. In control rats of both strains, the expression of the proANP mRNA was higher in the atria than in ventricles. In SD rats with the intact HPA axis, an upregulation of ANP gene expression was observed in the right atrium after IS1, in both atria and the left ventricle after IS3 and in the left atrium and the left ventricle after ICS3. In LE rats with a blunted reactivity of the HPA axis, no increase or even a downregulation of the gene expression was observed. Thus, acute stress-induced increase in the expression of the proANP gene is related to the activity of the HPA axis. It may have relevance to ANP-induced protection of the heart.

Discontinuous versus continuous drinking of ethanol in peripubertal rats: effect on 24-hour pattern of hypophyseal-gonadal axis activity and anterior pituitary oxidative stress

AIMS

Discontinuous (weekend) consumption of alcohol is common in adolescents and young adults. This study therefore assesses, in peripubertal male rats, the effect of discontinuous as compared to chronic feeding of ethanol or control liquid diet.

METHODS

Animals received an ethanol liquid diet (6.2 % w/v) starting on day 35 of life. Every week for 5 weeks, the discontinuous ethanol group received the ethanol diet for 3 consecutive days and the control liquid diet for 4 days. At the 5th week, 24 h after the last ethanol administration to the discontinuously ethanol-treated animals, rats were killed at 4-hour intervals beginning at 09.00 h. Chronically administered rats received the ethanol diet until immediately before study.

RESULTS

Disrupted 24-hour rhythmicity together with a significant nocturnal increase in plasma luteinizing hormone (LH), testosterone and prolactin (PRL) occurred in the discontinuous ethanol group. Plasma ethanol levels were undetectable at 24 h after the last ethanol treatment. In contrast, after chronic ethanol administration, plasma PRL was increased late in scotophase while LH and testosterone decreased; blood ethanol levels were 2-fold greater than those in discontinuously ethanol-administered rats killed immediately after ethanol withdrawal. Circulating testosterone positively correlated with LH levels in control rats only. Chronic administration of ethanol significantly augmented mean expression of pituitary nitric oxide synthase (NOS)-2, heme oxygenase (HO)-1, Per1 and Per2 genes and disrupted their diurnal rhythmicity. Decreased NOS-1 and NOS-2 expression during scotophase, together with suppression of the rhythm in Per1 and Per2 expression, were found in the discontinuous ethanol group.

CONCLUSIONS

Abstinence after discontinuous drinking of alcohol in rats, as compared to chronic administration of ethanol, is accompanied by increases of plasma LH and testosterone, a greater PRL response and a less pronounced oxidative damage of the anterior pituitary.

Continuous versus discontinuous drinking of an ethanol liquid diet in peripubertal rats: effect on 24-h variation of lymph node and splenic mitogenic responses and lymphocyte subset populations

Excessive alcohol consumption continues to be a major public health problem, particularly in the adolescent and young adult populations. Generally, such a behavior tends to be confined to the weekends, to attain frequently binge drinking. This study in peripubertal male rats compares the effect of the discontinuous feeding of a liquid diet containing a moderate amount of ethanol (6.2% wt/vol) to that of continuous ethanol administration or a control diet, taking as end points the 24-h variations of plasma prolactin levels and mitogenic responses and lymphocyte subset populations in submaxillary lymph nodes and spleen. Animals received the ethanol liquid diet starting on day 35 of life, the diet being similar to that given to controls except for that maltose was isocalorically replaced by ethanol. Ethanol provided 36% of the total caloric content. Every week, the discontinuous ethanol group received the ethanol diet for 3 days and the control liquid diet for the remaining 4 days. After 4 weeks, rats were killed at six time intervals, beginning at 0900 h. A significant decrease of splenic cells' response to concanavalin A, and of lymph node and splenic cells' response to lipopolysaccharide was found in rats under the discontinuous ethanol regime, when compared with control- or ethanol-chronic rats. Under discontinuous ethanol feeding, mean values of lymph node and splenic CD8(+) and CD4(+)-CD8(+) cells decreased, whereas those of lymph node and splenic T cells, and splenic B cells, augmented. In rats chronically fed with ethanol, splenic mean levels of CD8(+) and CD4(+)-CD8(+) cells augmented. Both modalities of ethanol administration disrupted the 24 h variation in immune function seen in controls. Mean plasma prolactin levels increased by 3.6-fold and 8.5-fold in rats chronically or discontinuously fed with alcohol, respectively. The immune parameters examined in an additional group of rats fed regular chow and water ad libitum did not differ significantly from control liquid diet. The results support the view that the discontinuous drinking of a moderate amount of ethanol can be more harmful for the immune system than a continuous ethanol intake, presumably by inducing a greater stress as indicated by the augmented plasma prolactin levels observed.

The response of circulating brain natriuretic peptide to academic stress in college students

Brain natriuretic peptide (BNP), a cardiac peptide, has been implicated in the regulation of hypothalamic-pituitary-adrenocortical (HPA) responses to psychological stressors. The influence of academic stress on circulating concentration of the N-terminal fragment of BNP precursor (NT-proBNP), and in relation to the stress hormone (cortisol) response was studied in 170 college students undergoing major examinations. Just prior to the examination, we measured self-estimated stress level, systolic, and diastolic blood pressure (SBP, DBP), heart rate (HR), plasma levels of cortisol, and NT-proBNP. These parameters were compared to the participants' baseline measurements, taken at the same hour of a different 'control day', without a major examination to induce stress. Hemodynamic variables (SBP, DBP, and HR) increased on the examination day compared with baseline values ( p < 0.001). Circulating cortisol concentration increased before examinations (+42%, p < 0.001). The response to stress was marked by a significant decrease in plasma NT-proBNP concentration (-40%, p < 0.001). We found in males a significant interaction between the cortisol elevation with examination stress and the NT-proBNP reduction ( p = 0.02). In response to academic stress, the plasma cortisol elevation was accompanied by a marked reduction in plasma NT-proBNP level. These data may indicate that mental stress entails an interface between the HPA axis and the peripheral natriuretic peptide system, leading to reciprocating changes in circulating levels of the corresponding hormones.

Prolactin induces phosphorylation of the STAT5 in adrenal glands of Hatano rats during stress

AIMS

To investigate the signaling of prolactin (PRL) in the adrenal gland during stress in Hatano high- (HAA) and low-avoidance (LAA) rats.

MAIN METHODS

Adrenal glands of both strains were collected at 0, 15 and 30 min after stress. The protein levels of phosphorylated STAT5 and the mRNA levels of melanocortin receptor 2 (MC2R) and PRL receptor (PRLR) were analyzed. Furthermore, the effects of bromocriptine-induced hypoprolactinemia on adrenocortical responses to stress were investigated.

KEY FINDINGS

Adrenocorticotropic hormone (ACTH) concentrations in HAA were greater than LAA, while the difference in PRL concentrations were found only at 120 min after stress induction. No strain differences were observed in corticosterone or progesterone in response to stress. The stress-induced increase in MC2R mRNA expression was higher in HAA, but there was a lowered PRLR mRNA expression. STAT5 become highly phosphorylated in response to stress in both strains, but bromocriptine led to a reduction the STAT5 phosphorylation. Exposure to bromocriptine was associated with a reduction in plasma PRL in response to stress in both strains, while the ACTH levels were not altered. However, the decrease in corticosterone and progesterone in response to stress was observed only in bromocriptine-treated LAA rats.

SIGNIFICANCE

These data show that PRL plays an important role in the regulation of corticosterone and progesterone release in LAA but not in HAA during stress. These results suggest that PRL increase in response to stress, and it acts on the adrenal cortex and thereby plays an important physiologic role in protecting against acute stress.

Evolutionary shifts in courtship pheromone composition revealed by EST analysis of plethodontid salamander mental glands

Courtship behavior in salamanders of the family Plethodontidae can last more than an hour. During courtship, males use stereotyped behaviors to repeatedly deliver a variety of proteinaceous pheromones to the female. These pheromones are produced and released from a specialized gland on the male's chin (the mental gland). Several pheromone components are well characterized and represented by high frequency transcripts in cDNA pools derived from plethodontid mental glands. However, evolutionary trends in the overall composition of the pheromonal signal are poorly understood. To address this issue, we used random sequencing to survey the pheromone composition of the mental gland in a representative species from each of three distantly related plethodontid genera. We analyzed 856 high-quality expressed sequence tags (ESTs) derived from unamplified primary cDNA libraries constructed from mental glands of Desmognathus ocoee, Eurycea guttolineata, and Plethodon shermani. We found marked differences among these species in the transcript frequency for three previously identified, functional pheromone components: Plethodontid Receptivity Factor (PRF), Sodefrin Precursor-Like Factor (SPF), and Plethodontid Modulating Factor (PMF). In P. shermani mental glands, transcripts predominately encoded PMF (45% of all ESTs) and PRF (15%), with less than 0.5% SPF. In contrast, in D. ocoee and E. guttolineata the proportions were approximately 20% SPF, 5% PMF, and PRF was absent. For both D. ocoee and E. guttolineata, peptide hormone-like transcripts occur at high frequency and may encode peptides that change the physiological state of the female, influencing the female's likelihood to complete courtship. These and previous results indicate that the evolution of courtship pheromones in the Plethodontidae is dynamic, contrasting with the predominant mode of evolutionary stasis for courtship behavior and morphology.

In vitro effects of homologous natriuretic peptides on growth hormone and prolactin release in the tilapia, Oreochromis mossambicus

C-type natriuretic peptide (CNP) cDNA was cloned from the tilapia brain and its inferred mature sequence was chemically synthesized together with previously cloned tilapia A-type and B-type natriuretic peptides (ANP and BNP). The cloned CNP belongs to the CNP-1 type of teleosts. Reverse-transcription polymerase chain reaction showed that the ANP and BNP genes were hardly expressed in the tilapia brain and pituitary, whereas the CNP gene was expressed strongly in the brain and slightly in the pituitary. Effects of homologous natriuretic peptides (100 nM each) on growth hormone (GH) and prolactin (PRL) release were examined using dispersed tilapia pituitary cells. Tilapia ANP and BNP stimulated GH and PRL release during 4-8, and 8-24 h of incubation. BNP appeared to be more potent than ANP, also stimulating GH and PRL release during 0-4 h of incubation. CNP stimulated GH release only during 4-8 h of incubation; CNP was without effect on PRL release. All three NPs stimulated GH and PRL mRNA expression in dispersed pituitary cells following 24 h of incubation. ANP and BNP significantly elevated intracellular cGMP accumulation in dispersed pituitary cells after 15 min of exposure, whereas no effect of CNP was observed. These results indicate a long-lasting stimulation of GH and PRL release by ANP and BNP that is mediated, at least in part, by the guanylyl cyclase-linked NP receptor.

Protein and peptide parenteral controlled delivery

Protein and peptide delivery has been a challenge due to their limited stability during preparation of formulation, storage and in vitro and in vivo release. These biopolymers have traditionally been administered via intramuscular or subcutaneous routes. Recent efforts have been made to develop formulations for non-invasive routes of administration, including oral, intranasal, transdermal and transmucosal delivery. Despite these efforts, invasive delivery remains the main method of administering peptide and protein drugs. This review focuses on recent developments in injectable, polymeric controlled-release formulations, with an emphasis on hydrogels and particulate systems.

Social condition affects hormone secretion and exploratory behavior in rats

Studies of behavior, endocrinology and physiology have described experiments in which animals housed in groups or in isolation were normally tested individually. The isolation of the animal from its group for testing is perhaps the most common situation used today in experimental procedures, i.e., there is no consideration of the acute stress which occurs when the animal is submitted to a situation different from that it is normally accustomed to, i.e., group living. In the present study, we used 90 male 120-day-old rats (Rattus norvegicus) divided into 5 groups of 18 animals, which were housed 3 per cage, in a total of 6 cages. The animals were tested individually or with their groups for exploratory behavior. Hormones were determined by radioimmunoassay using specific kits. The results showed statistically significant differences between testing conditions in terms of behavior and of adrenocorticotrophic hormone (ACTH: from 116.8 +/- 15.27 to 88.77 +/- 18.74 when in group and to 159.6 +/- 11.53 pg/ml when isolated), corticosterone (from 561.01 +/- 77.04 to 1036.47 +/- 79.81 when in group and to 784.71 +/- 55.88 ng/ml when isolated), luteinizing hormone (from 0.84 +/- 0.09 to 0.58 +/- 0.05 when in group and to 0.52 +/- 0.06 ng/ml when isolated) and prolactin (from 5.18 +/- 0.33 to 9.37 +/- 0.96 when in group and to 10.18 +/- 1.23 ng/ml when isolated) secretion, but not in terms of follicle-stimulating hormone or testosterone secretion. The most important feature observed was that in each cage there was one animal with higher ACTH levels than the other two; furthermore, the exploratory behavior of this animal was different, indicating the occurrence of almost constant higher vigilance in this animal (latency to leave the den in group: 99.17 +/- 34.95 and isolated: 675.3 +/- 145.3 s). The data indicate that in each group there is an animal in a peculiar situation and its behavior can be detected by ACTH determination in addition to behavioral performance.

Atrial natriuretic peptide mediates oxytocin secretion induced by osmotic stimulus

Atrial natriuretic peptide (ANP), first discovered in the heart, has been also detected in various brain regions involved in the control of cardiovascular function and water and sodium balance. The anteroventral region of the third ventricle (AV3V) and the subfornical organ (SFO) have ANP-immunoreactive projections towards the paraventricular (PVN) and supraoptic (SON) nuclei of the hypothalamus. Extracellular fluid (ECF) hyperosmolality stimulates the secretion of oxytocin (OT) which induces ANP release by the atrium. On the other hand, passive immunoneutralization of ANP reduces OT secretion in response to ECF hypertonicity. Previous studies have shown the co-localization of ANP and OT in PVN and SON neurons and in the periventricular region, as well as the presence of ANPergic and oxytocinergic neurons in the median eminence. The aim of the present study was to investigate the OT and ANP content in the SON and PVN of the hypothalamus and in the posterior pituitary (PP) after an osmotic stimulus that induces OT secretion. The results showed that intracerebroventricular microinjection of normal rabbit serum (NRS) or of ANP antiserum followed or not by an intraperitoneal injection of isotonic saline did not alter OT secretion or OT content in the PVN, SON, and PP; passive ANP immunoneutralization reduced the basal content of ANP in the PVN, SON, and PP of animals in a situation of isotonicity; the ANP antiserum inhibited the increase of OT secretion and content of OT and ANP in the PVN, SON and PP induced by the osmotic stimulus. Thus, the increase in plasma OT and oxytocinergic neurons of the hypothalamus-posterior pituitary system in response to hypertonicity depends on the action of endogenous ANP, i.e., ECF hypertonicity must activate ANPergic neurons which directly or indirectly stimulate OT release.

Hypothalamic atrial natriuretic peptide and secretion of oxytocin

Our study corroborated previous findings on the distribution of ANP and co-localization of ANP and OT in hypothalamic magnocellular neurons. We detected ANP/OT in smaller cells which apparently corresponded to parvocellular neurons and additionally a massive group of ANP immunoreactive fibers from periventricular regions to the median eminence, here closely associated with oxytocinergic fibers originated from PVN. ANP immunoneutralization did not change the basal OT level but blocked the OT secretion normally induced by osmotic stimulus. Thus, endogenous hypothalamic ANP seems necessary to stimulate OT release in the hyperosmolality condition.

Prolactin: structure, function, and regulation of secretion

Prolactin is a protein hormone of the anterior pituitary gland that was originally named for its ability to promote lactation in response to the suckling stimulus of hungry young mammals. We now know that prolactin is not as simple as originally described. Indeed, chemically, prolactin appears in a multiplicity of posttranslational forms ranging from size variants to chemical modifications such as phosphorylation or glycosylation. It is not only synthesized in the pituitary gland, as originally described, but also within the central nervous system, the immune system, the uterus and its associated tissues of conception, and even the mammary gland itself. Moreover, its biological actions are not limited solely to reproduction because it has been shown to control a variety of behaviors and even play a role in homeostasis. Prolactin-releasing stimuli not only include the nursing stimulus, but light, audition, olfaction, and stress can serve a stimulatory role. Finally, although it is well known that dopamine of hypothalamic origin provides inhibitory control over the secretion of prolactin, other factors within the brain, pituitary gland, and peripheral organs have been shown to inhibit or stimulate prolactin secretion as well. It is the purpose of this review to provide a comprehensive survey of our current understanding of prolactin's function and its regulation and to expose some of the controversies still existing.

Prolactin and corticosterone secretion in response to acute stress after paraventricular nucleus lesion by ibotenic acid

The cellular organization of the paraventricular nucleus (PVN) is complex and eight distinct regions have been identified by Nissl staining. Three consist of magnocellular neurons and five of parvocellular neurons. Ibotenic acid, a glutamate analogue, is a toxin with neuroexcitatory properties which acts on N-methyl-D-aspartate and metabotropic receptors. Depending on the dose used, ibotenic acid causes extensive damage of parvocellular neurons of the paraventricular nucleus but preserves magnocellular neurons and passage fibers, in contrast to electrolytic lesions, which causes diffuse and nonspecific destruction. We studied the prolactin (PRL) and corticosterone secretion in response to acute stress induced by exposure to the ether, 3 weeks after selective neurotoxic lesion of parvocellular neurons of the paraventricular nucleus by microinjection of ibotenic acid. There was no significant difference in the basal levels of PRL and corticosterone between control and lesioned animals. The plasma PRL increased in the sham and lesioned groups after stress of similar manner. However, the increase in plasma corticosterone in response to stress was significantly higher in lesioned animals. In conclusion, the selective lesion of parvocellular neurons of the PVN did not change basal or stress induced PRL secretion but it caused hypersensitivity of the hypothalamus-pituitary-adrenal axis 3 weeks later, probably by corticotropin releasing hormone (CRH) from hypothalamic areas others than parvocellular neurons of the PVN; hypersensitivity of corticotropes to the secretagogues others than CRH; or hyperresponsiveness of AVP receptors in the adenohypophysis. Furthermore, we cannot rule out a putative inhibitory factor of the hypothalamus-pituitary axis produced by parvocellular neurons of the PVN. This factor modulator of corticotropin secretion could be absent after recuperation of the response of the hypothalamus-pituitary axis to the stress.

Detailed localization of aquaporin-4 messenger RNA in the CNS: preferential expression in periventricular organs

We have performed a detailed in situ hybridization study of the distribution of aquaporin-4 messenger RNA in the CNS. Contrary to expectation, we demonstrate that aquaporin-4 is ubiquitously expressed in the CNS. Strong hybridization labeling was detected in multiple olfactory areas, cortical cells, medial habenular nucleus, bed nucleus of the stria terminalis, tenia tecta, pial surface, pontine nucleus, hippocampal formation and multiple thalamic and hypothalamic areas. A low but significant hybridization signal was found, among others, in the choroid plexus of the lateral ventricles, ependymal cells, dorsal raphe and cerebellum. Overall, a preferential distribution of aquaporin-4 messenger RNA-expressing cells was evident in numerous periventricular organs. From the distribution study, the presence of aquaporin-4 messenger RNA-expressing cells in neuronal layers was evident in neuronal layers including the CA1 -CA3 hippocampal pyramidal cells, granular dentate cells and cortical cells. Further evidence of neuronal expression comes from the semicircular arrangement of aquaporin-4 messenger RNA-expressing cells in the bed nucleus of the stria terminalis and medial habenular nucleus exhibiting Nissl-stained morphological features typical of neurons. Combined glial fibrillary acidic protein immunohistochemistry and aquaporin-4 messenger RNA in situ hybridization demonstrated that aquaporin-4 messenger RNA is expressed by glial fibrillary acidic protein-lacking cells. We conclude that aquaporin-4 messenger RNA is present in a collection of structures typically involved in the regulation of water and sodium intake and that aquaporin-4 water channels could be the osmosensor mechanism responsible for detecting changes in cell volume by these cells.

Hypertension associated with decreased testosterone levels in natriuretic peptide receptor-A gene-knockout and gene-duplicated mutant mouse models

Mice lacking the gene (Npr1) encoding the natriuretic peptide receptor A (NPRA) have hypertension with elevated blood pressure and cardiac hypertrophy. In particular, Npr1 gene-deficient male mice exhibit lethal vascular events similar to those seen in untreated human hypertensive patients. Serum testosterone levels tend to be lower in hypertensive male humans than in normal males without hypertension, but the genetic basis for this tendency remains unknown. To determine whether Npr1 gene function affects the testosterone level, we measured serum testosterone in male hypertensive mice lacking a functional Npr1 gene, wild-type animals with two copies, and the gene-duplicated littermates expressing four copies of the gene. In the Npr1 gene-knockout (zero-copy) mice, the serum testosterone level was 62% lower than that in the two-copy control mice (80+/-10 ts. 120+/-14 ng/ml, respectively; P < 0.005). Serum testosterone in the four-copy mice was 144% (P < 0.005) of that in the two-copy wild-type control mice. To investigate the role of NPRA in testicular steroidogenesis, we analyzed atrial natriuretic peptide (ANP)-dependent guanylyl cyclase activation, accumulation of intracellular cGMP, and testosterone production in purified primary Leydig cells from animals with zero, two, or four copies of the Npr1 gene. Leydig cells lacking the Npr1 gene did not show ANP-stimulated guanylyl cyclase activation or cGMP accumulation and had no ANP-dependent testosterone production. ANP stimulation of Leydig cells from the four-copy males elicited a 2-fold greater production of cGMP compared to that in the two-copy wild-type counterparts (260+/-12 vs. 126+/-7 pmol/l x 10(6) cells; P < 0.001). Similarly, ANP-dependent testosterone production in Leydig cells was nearly twice as high in four-copy mice as in two-copy wild-type controls (561+/-18 vs. 325+/-11 ng/l x 10(6) cells; P < 0.001). ANP-dependent guanylyl cyclase activation and production of cGMP in Leydig cells increased progressively with the number of Npr1 gene copies. Our results establish the existence of an alternate mechanism for testicular steroidogenesis that is stimulated by NPRA-dependent cGMP signaling, in addition to that mediated by gonadotropins, via a cAMP pathway. These findings demonstrate the role of Npr1 gene function in the maintenance of serum testosterone levels and testicular steroidogenesis and provide a genetic link between hypertension associated with decreased NPRA and low testosterone levels.

Characterisation of the effects of natriuretic peptides upon ACTH secretion from the mouse pituitary

The involvement of natriuretic peptides in the regulation of ACTH secretion in mice hemi-pituitary preparations was investigated. Atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) all inhibited CRF (10(-9) M)-evoked ACTH secretion over a concentration range of 10(-12)-10(-10) M and also stimulated cyclic GMP accumulation over a concentration range of 10 (-8)-10(-5) M. CNP was the most effective both in the inhibition of ACTH secretion and in the stimulation of cyclic GMP accumulation. Coincubation of hemi-pituitaries with 8bromo-cyclic GMP (10(-4) M) completely inhibited CRF (10(-9) M)-evoked ACTH secretion. Northern blot analysis revealed that all three major isoforms of the natriuretic peptide receptors are expressed in the mouse pituitary. These results demonstrate that natriuretic peptides do inhibit CRF-stimulated ACTH secretion from mouse pituitary preparations. A role for cGMP in mediating this effect on hormone secretion is indicated but the discrepancy between the efficacies of natriuretic peptides in inhibiting the secretory response and stimulating cyclic GMP accumulation suggest a more complicated stimulus-secretion coupling pathway is in operation.

Psychoneuroendocrinology of anxiety disorders

This article focuses on neuroendocrine measures in anxiety disorders and their relationships to neurotransmitter and neuroendocrine function. In particular, the hypothalamic-pituitary-somatotropin and the hypothalamic-pituitary-adrenal (HPA) axes are emphasized, and a role for extrahypothalamic corticotropin releasing factor is proposed. Additional neuroactive hormones are also considered. A nonhuman primate model of anxiety is discussed in terms of its neuroendocrine relevance. And, throughout, a hypothetical functional-anatomic model for anxiety and panic is proposed using the findings of cognitive neuroscience fear research. Finally, an effort is made to synthesize existing psychoneuroendocrinologic data into a current conceptualization of the pathophysiology of anxiety disorders.

Hypothalamic-pituitary-adrenocortical axis changes in a transgenic mouse with impaired glucocorticoid receptor function

Recently, a transgenic mouse with impaired glucocorticoid receptor (GR) function was created to serve as an animal model for the study of neuroendocrine changes occurring in stress-related disorders, such as major depression. Here, we investigated the hypothalamic-pituitary-adrenocortical (HPA) axis changes in these transgenic mice. There were no significant differences between basal early morning plasma ACTH and corticosterone levels in normal and transgenic mice. When animals were exposed to a mild stressor, an enhanced response in plasma ACTH was observed in the transgenic mice, whereas plasma corticosterone responses were not different. In view of these differences in plasma ACTH and corticosterone responses, we directed our studies toward the regulation of ACTH secretion on the hypothalamic-hypophyseal level in vitro. Therefore, an in vitro model, the pituitary-hypothalamic complex (PHc) was developed and its ACTH release profile was compared with that of the pituitary (PI) alone. The basal ACTH release by PHc and PI from normal and transgenic mice was similar. Regardless of the strain under study, the basal ACTH release by PI was significantly lower than the release by PHc. Stimulation of tissues with either high K+ (56 mM) or CRH (10 or 20 nM) produced an enhanced ACTH release from both PHc and PI, whereas the response in PI was larger than that in PHC. Moreover, the responses to these stimuli were markedly enhanced in tissues from transgenic mice. In tissues of normal mice, corticosterone inhibited both basal and CRH-stimulated ACTH release more potently in PHc than in PI. Furthermore, the feedback capacity of corticosterone to restrain both basal and CRH-stimulated ACTH release was highly impaired in tissues of transgenic mice, whereas the feedback in PHc appeared to be more affected than that in the PI of these animals. In conclusion, the in vitro data on PHc and PI revealed intrahypothalamic mechanisms operating 1) to fine-tune stimulus-evoked ACTH responses; and 2) to facilitate the negative feedback action of glucocorticoids. Moreover, in the transgenic tissues, the impaired GR function was found to cause augmented stimulus-evoked ACTH responses and an impaired glucocorticoid feedback efficacy which appeared to be mainly defective at the hypothalamic level. Thus, in the transgenic mice with life-long central GR dysfunction we found impaired negative feedback combined with "normal" (i.e. noncompensated) in vivo plasma corticosterone responses. This is a condition with potentially grave pathophysiological consequences and, therefore, this transgenic animal may be regarded as a valuable model for the study of functional glucocorticoid insufficiency at the central nervous system level.

Atrial natriuretic peptide and feeding activity patterns in rats

This review presents historical data about atrial natriuretic peptide (ANP) from its discovery as an atrial natriuretic factor (ANF) to its role as an atrial natriuretic hormone (ANH). As a hormone, ANP can interact with the hypothalamic-pituitary-adrenal axis (HPA-A) and is related to feeding activity patterns in the rat. Food restriction proved to be an interesting model to investigate this relationship. The role of ANP must be understood within a context of peripheral and central interactions involving different peptides and pathways.

Neuroendocrine regulation of salt and water metabolism

Neurons which release atrial natriuretic peptide (ANPergic neurons) have their cell bodies in the paraventricular nucleus and in a region extending rostrally and ventrally to the anteroventral third ventricular (AV3V) region with axons which project to the median eminence and neural lobe of the pituitary gland. These neurons act to inhibit water and salt intake by blocking the action of angiotensin II. They also act, after their release into hypophyseal portal vessels, to inhibit stress-induced ACTH release, to augment prolactin release, and to inhibit the release of LHRH and growth hormone-releasing hormone. Stimulation of neurons in the AV3V region causes natriuresis and an increase in circulating ANP, whereas lesions in the AV3V region and caudally in the median eminence or neural lobe decrease resting ANP release and the response to blood volume expansion. The ANP neurons play a crucial role in blood volume expansion-induced release of ANP and natriuresis since this response can be blocked by intraventricular (3V) injection of antisera directed against the peptide. Blood volume expansion activates baroreceptor input via the carotid, aortic and renal baroreceptors, which provides stimulation of noradrenergic neurons in the locus coeruleus and possibly also serotonergic neurons in the raphe nuclei. These project to the hypothalamus to activate cholinergic neurons which then stimulate the ANPergic neurons. The ANP neurons stimulate the oxytocinergic neurons in the paraventricular and supraoptic nuclei to release oxytocin from the neural lobe which circulates to the atria to stimulate the release of ANP. ANP causes a rapid reduction in effective circulating blood volume by releasing cyclic GMP which dilates peripheral vessels and also acts within the heart to slow its rate and atrial force of contraction. The released ANP circulates to the kidney where it acts through cyclic GMP to produce natriuresis and a return to normal blood volume.

Effect of plasma osmolality on pituitary-adrenal responses to corticotropin-releasing hormone and atrial natriuretic peptide changes in central diabetes insipidus

The objective of the present study was to examine the effect of changes in plasma osmolality (pOsm) on the responses of the pituitary-adrenal axis to CRH and atrial natriuretic peptide (ANP) release in patients with central diabetes insipidus (DI). Eight normal subjects and six DI patients were subjected to human CRH (hCRH) (1 microgram/kg) stimulation alone or associated with isotonic volume loading (0.9% NaCl, 12 mL.kg.60 min) or an osmotic stimulus (5% NaCl, 0.06 mL.kg/min.120 min). The DI group showed significantly increased pOsm and undetectable or low plasma arginine vasopressin (AVP) during all tests. In the control group, pOsm and plasma AVP increased only during the osmotic stimulus. The DI group presented lower plasma ANP levels than controls during osmotic stimulus and isotonic volume loading. The lower ANP secretion in DI patients corroborates the importance of neurohypophyseal hormones in ANP regulation. Basal plasma ACTH and cortisol levels did not differ between controls and DI. The latter group presented a higher ACTH response than controls during stimulation with hCRH alone [area under the curve (AUC) 1138 +/- 99 vs. 709 +/- 62 pmol.L/min] and hCRH/5% NaCl (AUC 1602 +/- 209 vs. 1158 +/- 187 pmol.L.min). The DI cortisol AUC were higher than controls during stimulation with hCRH alone (65,471 +/- 6,070 vs. 48,062 +/- 3,476 nmol.L.min) and hCRH/5% NaCl (89,005 +/- 10,043 vs. 62,105 +/- 5,600 nmol.L.min). The highest ACTH and cortisol responses to hCRH in both groups were obtained with hCRH/5% NaCl. There was a significant correlation between mean pOsm and ACTH response to hCRH (r = 0.62). The increased responses to hCRH with increasing pOsm were present in control subjects and in patients with DI. However, at any given level of pOsm, there was no difference in ACTH response between controls and DI. These data indicate that the acute increases in pOsm augmented the ACTH and cortisol responses to hCRH that involve other factors besides magnocellular AVP.

Immediate early gene induction by natriuretic peptides in PC12 phaeochromocytoma and C6 glioma cells

The effect of the natriuretic peptides ANP, BNP and CNP on cGMP formation and immediate early gene expression was investigated in PC12 phaeochromocytoma and C6 glioma cell lines. The three natriuretic peptides were shown to rapidly induce c-fos, TIS8/egr-1 and junB mRNA expression in both cell lines, via stimulation of the cGMP pathway. CNP stimulated cGMP formation and gene induction more potently than the other peptides in C6 cells, and this was statistically significant. In contrast, the three peptides produced similar gene induction in PC12 cells, despite the higher cGMP accumulation evoked by ANP or BNP. CNP was also found to increase DNA binding activity of the transcription factor AP1 in both cell types, demonstrating that natriuretic peptides potentially regulate key cellular gene expression.

Distribution of natriuretic peptide precursor mRNAs in the rat brain

Atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP) represent members of a recently discovered neuropeptide family involved in central regulation of endocrine and autonomic functions. The present study employed an in situ hybridization approach to provide the first detailed comparative mapping of ANP, BNP, and CNP mRNAs in brain. Results indicate that ANP mRNA is highly expressed in anterior olfactory nuclei, limbic cortices, dorsal endopiriform nucleus, hippocampal subfield CA1, cortical amygdaloid nuclei, medial habenula, anteroventral periventricular and arcuate nuclei, periventricular stratum, zona incerta, mammillary nuclei, inferior olive, nucleus ambiguus, and pontine paragigantocellular nuclei. CNP mRNA is expressed at highest levels in olfactory nuclei, limbic cortices, dorsal endopiriform nucleus, hippocampal subfields CA1-3, anteroventral periventricular and arcuate nuclei, and numerous brainstem regions (including the pontine, lateral reticular, solitary tract, prepositus hypoglossal, and spinal trigeminal nuclei). Positive labeling for BNP mRNA was not observed in brain. The presence of both ANP and CNP mRNA in the same regions of distinct nuclei (e.g., the anteroventral periventricular and arcuate nuclei) suggests the potential for coexpression. Overall, the present data are consistent with a prominent role for both ANP and CNP in neuroendocrine regulation and central cardiovascular integration. The extensive localization of ANP and/or CNP mRNA in olfactory nuclei, limbic cortex, hippocampus, amygdala and diencephalic limbic relays further indicate a putative role for ANP and CNP as neuromodulators of olfactory/limbic information processing.

Characterization of natriuretic peptide receptor subtypes in the AtT-20 pituitary tumour cell line

Receptors for the natriuretic peptide family have been characterized in the adrenocorticotrophic hormone (ACTH)-secreting AtT-20 pituitary tumour cell line. Northern blot analysis detected mRNA transcripts for the guanylate cyclase-linked GC-B receptor subtype. There was no evidence for the expression of either guanylate cyclase-linked GC-A receptor or atrial natriuretic peptide (ANP)-C (clearance) receptor mRNAs. Cyclic GMP production in AtT-20 cells was stimulated up to 200-fold by C-type natriuretic peptide (CNP), which was 10- and 20 times as effective as equivalent concentrations of brain natriuretic peptide and ANP respectively. Cyclic GMP dose-response curves to CNP failed to show any signs of saturation even at concentrations up to 30 microM, indicating a relatively low affinity of CNP for the GC-B receptor. Although CNP induced large stimulations in cyclic GMP production, specific binding of [125I-Tyr0]CNP could not be demonstrated in AtT-20 cells. The absence of specific binding with this radiolabelled analogue is possibly due to a reduced affinity for the GC-B receptor, as CNP analogues with N-terminal modifications such as [Tyr0]CNP and [127I-Tyr0]CNP exhibited reduced abilities to stimulate cyclic GMP production in these cells. Despite elevating cyclic GMP levels, CNP had no effect on basal or corticotrophin-releasing factor-stimulating ACTH release from the cells. These results show that the guanylate cyclase-coupled GC-B receptor is the only natriuretic peptide receptor subtype expressed in AtT-20 cells. Although CNP can markedly stimulate cyclic GMP production in these cells, there is incomplete expression of the normal natriuretic peptide-induced inhibitory pathway of ACTH secretion at some point distal to the production of cyclic GMP.