Plasma hormones (arginine vasotocin, prolactin, aldosterone, and corticosterone) in relation to hydration state, NaCl intake, and egg laying in fowls

Short-term dehydration influences baseline but not stress-induced corticosterone levels in the house sparrow (Passer domesticus)

Future environmental variations linked to climate change are expected to influence precipitation regimes and thus drinking water availability. Dehydration can be a particularly challenging physiological state for most organisms, yet no study has examined the effect of dehydration on the functioning of the hypothalamic-pituitary-adrenal axis in wild endothermic animals, despite its central role in maintaining homeostasis. In this study, we experimentally imposed a temporary water shortage (∼20 h) on captive house sparrows in order to investigate the consequences of short-term dehydration on baseline and stress-induced corticosterone levels. As expected, water-deprived birds displayed higher plasma osmolality and haematocrit. Additionally, water-deprived birds had lower defecation rates, suggesting that the mechanisms allowing caecal water absorption may be triggered very rapidly during water deprivation. Baseline but not stress-induced corticosterone levels were higher in water-deprived birds. Taken together, these results suggest that water restriction may have critical consequences on several corticosterone-related traits such as energy budget (protein catabolism and possibly feeding reduction), enhanced mobility (to promote water acquisition) and potential responses to predators (thirst threshold overriding the acute stress response). Owing to the possible fitness consequences of such components of the day-to-day life of birds, further studies should aim at investigating the influence of future changes in precipitation regimes and drinking water availability on bird populations.

Elevated temperatures are associated with stress in rooftop-nesting Common Nighthawk (Chordeiles minor) chicks

Grasslands and riparian forests in southeastern South Dakota have been greatly reduced since historical times, primarily due to conversion to row-crop agriculture. Common Nighthawk (Chordeiles minor) nesting habitat includes grasslands, open woodlands and urban rooftops, but nesting sites in southeastern South Dakota are confined to rooftops, as natural nesting habitat is limited. Nighthawks nesting on exposed rooftop habitats may encounter thermal conditions that increase operative temperatures relative to vegetated land cover types. Mean humidity has increased and mean wind speed and cloud cover have decreased during the nighthawk breeding season from 1948 to 2016 in southeastern South Dakota. These changes might contribute to increasing operative temperatures at exposed rooftop nest sites and this could influence chick condition. We studied nest micro-climate and the plasma stress response for 24 rooftop-nesting nighthawk chicks from 17 nests during 2015 and 2016. High humidity prior to blood collection reduced both baseline and stress-induced plasma corticosterone (CORT). In contrast, high maximum temperatures during the day before sampling increased stress-induced CORT. The magnitude of the chick stress response was significantly negatively related to maximum wind speed for the week prior to CORT measurement. Other weather and micro-climate variables were not significant effectors of CORT metrics. Most chicks had low baseline CORT and were able to mount a stress response, but a subset of chicks (n = 4) showed elevated baseline CORT and a negative association between the magnitude of stress response and ambient temperature. For this subset, mean ambient temperature for the day before sampling was significantly higher (2.3°C) than for chicks with typical baseline CORT levels. These data suggest that regional climate change trends could affect the ability of nighthawk chicks to mount a stress response, which, in turn, might influence the susceptibility of nighthawk chicks to climate change in the Northern Prairie region.

Diencephalic and septal structures containing the avian vasotocin receptor (V1aR) involved in the regulation of food intake in chickens, Gallus gallus

Recently, it was found that the avian central vasotocin receptor (V1aR) is associated with the regulation of food intake. To identify V1aR-containing brain structures regulating food intake, a selective V1aR antagonist SR-49059 that induced food intake was administrated intracerebroventricularly in male chickens followed by detection of brain structures using FOS immunoreactivity. Particularly, the hypothalamic core region of the paraventricular nucleus, lateral hypothalamic area, dorsomedial hypothalamic nucleus, a subnucleus of the central extended amygdalar complex [dorsolateral bed nucleus of the stria terminalis], medial septal nucleus and caudal brainstem [nucleus of the solitary tract] showed significantly increased FOS-ir cells. On the other hand, the supraoptic nucleus of the preoptic area and the nucleus of the hippocampal commissure of the septum showed suppressed FOS immunoreactivity in the V1aR antagonist treatment group. Further investigation revealed that neuronal activity of arginine vasotocin (AVT-ir) magnocellular neurons in the supraoptic nucleus, preoptic periventricular nucleus, paraventricular nucleus and ventral periventricular hypothalamic nucleus and most likely corticotropin releasing hormone (CRH-ir) neurons in the nucleus of the hippocampal commissure were reduced following the antagonist treatment. Dual immunofluorescence labeling results showed that perikarya of AVT-ir magnocellular neurons in the preoptic area and hypothalamus were colabeled with V1aR. Within the nucleus of the hippocampal commissure, CRH-ir neurons were shown in close contact with V1aR-ir glial cells. Results of the present study suggest that the V1aR plays a role in the regulation of food intake by modulating neurons that synthesize and release anorectic neuropeptides in the avian brain.

Age, photoperiod and estrogen dependent variations in the shell gland and the expression of AVT in the ovary of Japanese quail

Present work was undertaken to describe (i) age dependent (prepuberal-3, 4, 5 and 6 weeks old, puberal and actively laying 8 and 12 weeks old and aged 78 weeks old) (ii) photoperiodic response dependent (photosensitive and photorefractory) and sex steroid dependent (estradiol benzoate and its antagonist tamoxifen treated) variation in the ovary and shell gland activity of Japanese quail (Coturnix coturnix japonica). Further, in view of the role of neurohypophysial peptide arginine vasotocin (AVT) in many physiological processes including age/reproduction related oviposition, expression of ir-AVT was also monitored in the ovary of quail. All the parameters associated with histodifferentiation increased rapidly during the developing stages followed by a decrease in old age, which also increased in reproductively quiescent photorefractory birds following estradiol treatment and decreased in reproductively active photosensitive quail following tamoxifen treatment. Using AVT-specific antibody, expression of immunoreactive AVT (ir-AVT) observed in the ovary of photosensitive quail was not detected in the photorefractory quail. However, administration of estrogen in the photorefractory quail stimulated the growth and activity of ovary and shell gland also resulted in the expression of ovarian ir-AVT. On the other hand, tamoxifen eliminated the localization of ir-AVT in the ovary of photosensitive quail in addition to a decrease in the shell gland protein and alkaline phosphatase activity. It is concluded that estrogen not only affects the growth and differentiation of ovary and oviduct including shell gland but also regulates the expression of ovarian AVT. It is also suggested that in addition to reported paracrine effect of AVT in the shell gland of Japanese quail for oviposition, ovarian AVT may also affect ovarian function (ovulation), and in part, this regulation is estrogen dependent.

Corticosterone- or metapyrone-induced alterations in adrenal function and expression of the arginine vasotocin receptor VT2 in the pituitary gland of domestic fowl, Gallus gallus

The avian neurohypophyseal hormone arginine vasotocin (AVT) is known to be involved in the regulation of adrenocorticotropin (ACTH) release by interacting with the VT2 receptor (VT2R), which is homologous to the mammalian vasopressin V1b receptor (V1bR). To study the role of glucocorticoid in the expression and regulation of the VT2R, corticosterone (1 or 5mg/bird/day) or metapyrone (10 or 50mg/kg body weight/day) were administered daily for 8 days to white leghorn chickens. While low doses were ineffective, a high dose of corticosterone upregulated, while metapyrone downregulated, pituitary VT2R mRNA expression and ir-VT2 in the cephalic lobe of the anterior pituitary. Further, although no change was observed in the expression of POMC mRNA, adrenal activity (as judged by the changes in total cholesterol, 3beta HSD, cortical cord width and cortico-medullary ratio) exhibited suppression or stimulation following treatment with corticosterone or metapyrone, respectively. In view of the classical negative feedback effect of glucocorticoids at the level of hypothalamic CRH neurons and pituitary corticotrophs, high corticosterone level-induced suppression of the CRH-ACTH axis may have been masked by VT2R-mediated stimulation of corticotrophs, and hence the POMC mRNA level did not change. The same argument could be used for metapyrone. It is concluded that expression of the VT2 receptor is regulated by glucocorticoids in chicken. These findings confirm a role for AVT, mediated by the VT2 receptor, in regulating ACTH secretion during stress and suggest that corticotroph VT2 receptor levels may be dynamically regulated depending on the HPA axis activity.

Effect of estrogen and its antagonist on the expression of arginine vasotocin (AVT) and its oxytocic-like receptor VT3 in the shell gland of Japanese quail, Coturnix coturnix japonica

Avian neurohypophysial hormone arginine vasotocin (AVT) is known to regulate shell gland contractility during oviposition. While studying the role of estrogen in the expression and regulation of AVT and its oxytocic-like receptor VT3, using in situ hybridization and immunohistochemistry, it was observed that the expression of AVT and its receptor was not detected in the shell gland of sexually immature Japanese quail. However, administration of estrogen to these birds not only stimulates the growth and activity (as assessed by increased mucosal fold length, total protein content and alkaline phosphatase level) of the shell gland but also upregulates the expression of AVT and VT3. Further, administration of estrogen antagonist tamoxifen to sexually mature bird shows opposite results. On the other hand, localization of ir-AVT, observed in the ovary of sexually mature bird, was not detected in the estrogen treated sexually immature quail. It is concluded that estrogen not only affects the growth and differentiation of avian oviduct, but also regulates the expression of shell gland AVT and its receptor VT3. Present findings suggest that the locally synthesized AVT acts in a paracrine way to upregulate VT3 receptor and thus facilitates the endocrine function of neurohypophysial AVT during oviposition.

Changes in vasotocin immunoreactivity of paraventricular nuclei and adrenal function of Japanese quail in relation to different phases of sexual development

In relevance to osmoregulatory and reproductive functions, activity of hypothalamic neurosecretory neurons may also vary seasonally. The current study was performed to determine annual changes in ir-AVT neurons of hypothalamus and adrenal gland function. We examined changes in ir-AVT neuron by immunohistochemical method and plasma testosterone was measured by enzyme immunoassay. The steroidogenic interrenal activity was studied by histological and biochemical methods. Birds were sampled in February (quiescent), April (recrudescent), June (breeding) and November (regressive). A significant and gradual increase in the number of ir-AVT neurons was observed from quiescent to breeding phase which decreased during regressive phase of annual gonadal cycle. The gradual increase in ir-AVT neurons along with annual gonadal activity of quail were accompanied by increase in plasma levels of testosterone. These results indicate a functional interaction between sex steroid and AVT synthesizing neurons. Adrenal activity (as judged by weight, ascorbic acid content, cortical cord width and cortico-medullary ratio) was also maximum during breeding phase. It is thus postulated that domesticated quail when exposed to natural day length (NDL), exhibits seasonal/annual cyclicity in vastocinergic activity and adrenal function which may be due to difference in sex steroid hormone.

Sex differences in plasma corticosterone release in undisturbed chickens (Gallus gallus) in response to arginine vasotocin and corticotropin releasing hormone

In birds, two neuropeptides, corticotropin releasing hormone (CRH) and arginine vasotocin (AVT), are major regulators of the hypothalamo-pituitary-adrenal axis (HPA) during the stress response. In birds, however, the relative efficacy of CRH and AVT to stimulate the HPA axis in males and females remains unknown. The purpose of this study was to determine the time course of CORT release following central CRH and AVT administration to male and female chickens. Chickens were fitted with a stainless steel cannula surgically implanted in the lateral ventricle and a catheter chronically inserted in the jugular vein. Birds were housed individually in cages behind a one-way glass partition and unnecessary noise was avoided during the sampling period. Each bird received a single 5.0microtracerebroventricular (ICV) injection of either saline (SAL), AVT (10 and 100pmol), or CRH (10 and 100pmol). Blood was sampled remotely every 15min for 2h and plasma CORT was determined by radioimmunoassay. There was a significant increase in plasma CORT concentration in males injected with 100pmol AVT beginning at 15min post-injection through 2h compared with SAL injected birds. In males, injection of 100pmol CRH was significantly more effective in releasing CORT compared to an equal molar concentration of AVT or SAL. In females, ICV injection of 100pmol AVT induced moderate increase in CORT levels. In contrast, 100pmol CRH significantly increased plasma CORT compared to SAL injected controls but the CORT response was nearly 50% less than that obtained in males.

Effect of photoperiod and estrogen on expression of arginine vasotocin and its oxytocic-like receptor in the shell gland of the Japanese quail

The avian neurohypophysial hormone arginine vasotocin (AVT) is an important regulatory hormone involved in many physiological processes including fluid balance, blood pressure regulation, stress responses and reproductive events including oviposition. The mechanisms by which AVT stimulates myometrial contraction during oviposition are not well established in birds. In the present study, immunohistochemistry and in situ hybridization were used to localize AVT and the oxytocin-like VT3 receptor in the shell gland of Japanese quail (Coturnix coturnix japonica). Using an AVT-specific antibody, immunoreactive AVT (ir-AVT) was observed in the myometrium of both photosensitive and photorefractory birds. Similarly, VT3 receptor gene transcripts were detected in the myometrial layer of the shell gland of both photosensitive and photorefractory birds. Body mass, shell gland mass and length of mucosal folds of the shell gland of photosensitive birds was higher compared to that of photorefractory birds. Treatment of photorefractory birds with estrogen increased shell gland activity (mass and length of mucosal folds) and levels of both AVT and VT3 receptor mRNA, whereas treatment of photosensitive birds with the estrogen antagonist tamoxifen decreased shell gland activity and levels of both AVT and VT3 receptor mRNA. Our results suggest that shell gland contractility in response to AVT may be regulated during the reproductive cycle of the Japanese quail and that, in part, this regulation is estrogen-dependent.

Environmental regulation of the reproductive system in a flexibly breeding Sonoran Desert bird, the Rufous-winged Sparrow, Aimophila carpalis

We investigated reproductive regulation in male Rufous-winged Sparrows, Aimophila carpalis, a Sonoran Desert passerine that breeds after irregular summer rains. Field and captive data demonstrate that increased photoperiod stimulates testicular development in March and maintains it until early September. Free-living birds caught in July and placed on captive long days (16L: 8D) maintained developed testes for up to 7 months, and free-living birds caught in September, during testicular regression, redeveloped testes when placed on captive long days, indicating that these birds were still photosensitive. Captive birds on long days maintained testicular development when exposed to temperatures mimicking those occurring during regression in free-living birds. In free-living birds, testicular development was observed during spring and summer, but unless this was associated with rainfall, breeding (indicated by juveniles) did not occur. Large increases in plasma luteinizing hormone (LH) in free-living males were correlated with heavy rainfall in July/August, when the birds bred, and in November, when they did not breed. In captive birds, plasma LH concentrations were unresponsive to photoperiodic changes, but may have responded to social cues. Plasma prolactin concentrations were directly correlated with photoperiod in free-living birds, but an effect of photoperiod on prolactin secretion was not seen in captive birds. It is concluded that male Rufous-winged Sparrows use long photoperiods to stimulate and maintain testicular development, but exposure to long photoperiods does not terminate breeding by inducing absolute photorefractoriness. The specific timing of reproductive behaviors is apparently determined by elevated plasma LH coinciding with long day stimulated gonad development.

Regulation of the avian kidney by arginine vasotocin

Nonapeptides secreted by the neurohypophysis have important roles in vertebrate cardio-fluid homeostasis. In birds, those peptides include mesotocin (the representative of the neutral, or oxytocin-like, nonapeptide family) and vasotocin (the representative of the basic, or vasopressin-like, hormones). The function of mesotocin is not well defined, but it does appear to have osmoregulatory functions. Vasotocin is considered the primary avian antidiuretic hormone. Receptors for AVT in avian kidney-either on renal vasculature or on the tubules-have yet to be localized or identified. However, AVT quite certainly effects antidiuresis via both vascular and tubular mechanisms. The former entail a reduction in the rate of glomerular filtration, apparently via constriction of afferent arterioles. Evidence for the latter (direct tubular action of AVT) has accumulated in recent years and includes enhanced fractional tubular water reabsorption, activation of second messenger (cAMP) in thick ascending limbs and collecting ducts, and modest AVT-stimulated water permeability in collecting ducts associated with expression of aquaporins. The relative importance of the renal vascular vs. tubular actions in birds likely depend on the dose of the hormone, the physiological condition of the animal, and the species of bird.

The cloned avian neurohypophysial hormone receptors

Arginine vasotocin (AVT), a neurohypophysial hormone, has many essential functions in birds including the regulation of salt and fluid balance, blood pressure, the stress response and a variety of behaviors. In addition, AVT controls reproductive functions in birds that are served by oxytocin in mammals. In the following review, we examine the functions of AVT in birds with an emphasis on the present state of knowledge concerning the cloned receptors for this important hormone. Receptor and gene structure, signal transduction mechanisms and expression pattern are all discussed. Finally, we explore the phylogenetic relationships between the cloned avian receptors and other vertebrate and invertebrate neurohypophysial hormone receptors.

Direct action of parathyroid hormone-related peptide to enhance corticosterone production stimulated by adrenocorticotropic hormone in adrenocortical cells of hens

The presence of receptor for chicken parathyroid hormone-related peptide (cPTHrP) in the cortical cells of the adrenal gland of the hen was demonstrated by radioligand binding assays. When the cortical cells were incubated in vitro with chicken adrenocorticotropic hormone (cACTH) in the presence of cPTHrP, greater production of corticosterone was observed than when incubated with cACTH alone. The results suggest that PTHrP may act directly on the adrenocortical cells via its receptor binding and increase the response to ACTH for corticosterone secretion in the hen.

Changes in expression of AVT and AVT receptor (VT1) gene in hypothalamus and shell gland in relation to egg laying in white leghorn hen

Oviposition is a complex phenomenon involving various regulatory mechanisms at the neuroendocrine levels. Present study was designed to access the changes in arginine vasotocin (AVT) and its receptor (VT1) gene expression in relation to the time of egg laying of white leghorn hen. The expression of AVT gene (Northern blot analysis and in situ hybridization) in the hypothalamus and localization of ir-AVT in the magnocellular neurons of paraventricular nuclei was studied 2 h before (-2 h), immediately after (0 h) and 2 h after (+2 h) egg laying. Simultaneous changes in the AVT and VT1 receptor gene in the shell gland, which finally responds to AVT for smooth muscle contraction and expulsion of egg, were also determined by semi-quantitative reverse transcriptase-polymerase chain reaction. The findings indicated increased hypothalamic AVT gene expression immediately after egg laying (0 h) when compared to 2 h before and 2 h after egg laying. AVT receptor gene expression in the shell gland also followed the same pattern. However, AVT gene expression in the shell gland, unlike that of hypothalamus was higher at -2 h compared to 0 and +2 h of oviposition. While highly significant increase was noted in plasma AVT concentration at the time of egg laying, other parameters such as plasma osmolality and ionic concentration (Na(+), K(+), Ca(2+), and Cl(-)) did not show any change. It is suggested that in addition to increased hypothalamic AVT transcript and peripheral release, local synthesis of AVT in the shell gland (paracrine release) may contribute to the contraction of shell gland smooth muscles during egg laying. Moreover, these findings clearly indicate temporal correlation of AVT and its receptor gene expression in different tissues during oviposition.

Effects of cadmium ingestion on plasma and osmoregulatory hormone concentrations in male and female Pekin ducks

Effects of ingested cadmium (Cd) on body mass and plasma, urine, salt-gland secretion, and osmoregulatory hormone concentrations were assessed in male and female Pekin ducks, Anas platyrhynchos, acclimated to 450 mM NaCl over 6 wk and then held an additional 13 wk on 300 mM NaCl (prolonged saline exposure). Groups of six birds ate diets containing 0 (control), 50 (low-Cd diet), or 300 (high Cd diet) micrograms Cd/g food. Ducks that ingested Cd, especially females, lost body mass. Cadmium ingestion did not affect salt-gland secretion concentration. Control males had higher plasma osmolality and lower relative plasma volume. These increased in both sexes during saline acclimation. The high-Cd diet suppressed the increase in plasma osmolality in both sexes, but a rise in relative plasma volume occurred only in females. Following prolonged exposure to saline, plasma osmolality and relative plasma volume were reduced in control ducks but further elevated in ducks on the high-Cd diet. Cadmium ingestion suppressed the increase in urine osmolality that occurred in control ducks during saline acclimation. Neither saline acclimation nor Cd ingestion affected plasma concentrations of arginine vasotocin or prolactin. Arginine vasotocin was not correlated with plasma osmolality; prolactin was negatively correlated with plasma osmolality, but only in males. Cadmium suppressed the increase in angiotensin II that occurred at higher salinities in control and low-Cd males. This study examined the effects of gradually increasing body cadmium content on osmotic homeostasis. Cadmium affected plasma and urine, but not salt-gland secretion, concentrations and some of these responses were sexually disparate. Cadmium did not affect osmoregulatory hormones (arginine vasotocin and prolactin) by which observed changes in plasma concentration might have been influenced.

Sex dimorphism in the avian arginine vasotocin system with special emphasis to the bed nucleus of the stria terminalis

The avian neuropeptide arginine vasotocin (AVT) originally characterized as the antidiuretic hormone (, Endocrinol. 66, 860-871) is produced by neurosecretory cells within the brain. Numerous neuroanatomical studies that employed immunocytochemical and in situ hybridization techniques revealed such cells in the following anatomical brain locations: (a) preoptic area including supraoptic nucleus; (b) paraventricular nucleus; (c) the bed nucleus of the stria terminalis (BnST) (, J. Hirnforsch. 27, 559-566;, J. Neuroendcrinol. 5, 281-288;, Cell Tiss. Res. 287, 69-77;, J. Comp. Neurol. 369, 141-157). The BnST which influences reproduction and sexual behavior shows sex differences in morphology, steroid responsiveness and synthesis of neuropeptides including AVT (, Brain Res. 657, 171-184). AVT is the main endocrine regulator of fluid balance in avian species and, in addition, is involved in oviposition in these species. Our recent studies clearly demonstrated that AVT secretion after osmotic stimulation is sexually dimorphic. In order to investigate whether AVT is expressed and synthesized in the BnST in a sexually dimorphic manner we have used in situ hybridization technique and immunocytochemistry to analyze AVT gene expressing neurons in the parvocellular (small-celled nulei) BnST of adult male and female chickens. In cocks, AVT peptide-containing neurons were detected in the parvocellular BnST and the lateral septal area, whereas no AVT immunoreactive neurons were detected in the corresponding regions of the hen. Even after osmotic stimulation AVT gene expression in neurons of the parvocellular BnST of hens was not upregulated (, Cell Tiss. Res. 287, 69-77). These results demonstrate: (a) AVT gene expression in the BnST of chickens; and (b) a strong sexual dimorphism in this region. Furthermore, AVT synthesis is regulated on the transcriptional level independent from osmotic stimuli. Thus, sex steroids might be the main regulator of AVT gene expression in the BnST. In this paper we not only review the sexual dimorphic vasotocinergic system in the BnST, we also focus on the ontogeny of sex differences and the role of gonadal hormones in organization and retention of these differences.

The effects of highly selective opioid receptor antagonists on the release of arginine vasotocin induced by hyperosmotic stimulation and angiotensin II injection

The effects of highly selective antagonists to mu-, delta-, and kappa-opioid receptor subtypes on hyperosmotic- or angiotensin II (AII)-induced arginine vasotocin (AVT) release were investigated in chicks. Plasma levels of AVT increased about 1.5-fold after the administration of 1.5 M NaCl (200 microl, ip) or 100 ng AII (5 microl, icv). The administration of the mu-antagonist naloxonazine and the kappa-antagonist nor-Binaltorphimine further elevated plasma levels of AVT stimulated by hypertonic NaCl or AII. These effects of mu- and kappa-opioid receptor antagonists on AVT release were dose dependent. Nor-Binaltorphimine enhanced hyperosmotically stimulated plasma levels of AVT at a lower dose than that of naloxonazine. Conversely, the delta-selective antagonist naltrindole did not significantly affect AVT secretion. None of the opioid receptor antagonists influenced basal plasma levels of AVT. Therefore, these results suggest that mu- and kappa-opioid receptors are involved in hyperosmotic- and AII-induced AVT release, and the effect of the kappa-opioid receptor antagonist in the AVT release stimulated by hyperosmolality is strong compared to that of the mu-opioid receptor antagonist.

A sexual dimorphism in hypothalamic arginine vasotocin (AVT) gene expression and AVT plasma levels in the Japanese quail (Coturnix coturnix japonica) in response to water deprivation

To examine a possible sexual dimorphism in the osmotic control of arginine vasotocin (AVT) release in birds, age-matched male and female Japanese quail were subjected to water deprivation. The observed increased plasma osmolalities were accompanied by increased plasma AVT levels. Plasma mesotocin levels did not change with water deprivation. The sensitivity of the osmotic control of AVT release as determined by the slope of the relationship between plasma AVT levels and plasma osmolalities was significantly (P < 0.05) higher in males than in females. By Northern blot analysis, levels of hypothalamic AVT gene transcripts were increased 2.3 +/- 0.14- and 3.5 +/- 0.13-fold in water-deprived male and female Japanese quail, respectively, compared to normally hydrated birds. Our data suggest gender-related differences in the osmotic control of AVT release and in hypothalamic AVT gene expression in the Japanese quail.

Effects of short-term dehydration on plasma osmolality, levels of arginine vasotocin and its hypothalamic gene expression in the laying hen

The neurohypophysial hormone, arginine vasotocin (AVT), plays an important role in the osmoregulation of birds. After a prolonged period of water deprivation, plasma osmolality and plasma concentration of AVT are elevated. In this study, the effects of short term dehydration were examined in laying hens by measuring plasma osmolality, plasma levels of potassium, sodium and AVT and hypothalamic concentrations of mRNA encoding AVT during 8 h of water deprivation. Plasma osmolality increased significantly after at 6 h of water deprivation. Plasma sodium levels, however, did not change. Plasma potassium concentrations gradually decreased during dehydration. Plasma AVT levels and hypothalamic AVT mRNA levels increased significantly after 8 h. The results of this study demonstrate that depriving chickens of water results first in an increase in plasma osmolality followed by increases in AVT levels in plasma and AVT mRNA levels in the hypothalamus. The data indicate that the synthesis of AVT in the magnocellular neurons in the hypothalamus is activated soon after the animals are deprived of water. This indicates that both de novo synthesized AVT as well as AVT stored in the neurohypophysis are available to meet the increasing demands for the hormone during osmotic stress.

Changes of AVT levels in plasma, neurohypophysis and hypothalamus in relation to oviposition in the laying hen

Arginine vasotocin (AVT) is a neurohypophysial hormone involved in the reproductive function in avian species. We measured AVT concentrations in the neurohypophysis and plasma in relation to indomethacin blocked oviposition and to prostaglandin (PG) E2-induced premature oviposition in the hen. In addition, AVT concentration in the hypothalamus was measured in relation to spontaneous oviposition. In the control group the concentration of AVT decreased in the neurohypophysis and increased in plasma at oviposition. In hens that were administrated indomethacin, oviposition was delayed for several hours and no changes in the levels of AVT in neurohypophysis and plasma were observed at the predicted time of oviposition. Premature oviposition was induced within 5 min after the administration of PGE2. The levels of AVT decreased in the neurohypophysis and increased in plasma at the PGE2-injected premature oviposition. The increases of AVT levels in paraventricular and supraoptic nuclei were observed 2 and 5 h after spontaneous oviposition. The results indicate that oviposition causes an increase in the release of AVT from neurohypophysis and suggest that the synthesis of hypothalamic AVT may be stimulated by oviposition.

Antidiuretic hormone and angiotensin II plasma concentrations in febrile Pekin ducks

1. The objective of this study was to determine the changes in plasma concentrations of the hormones arginine vasotocin (AVT) and angiotensin II (AII) associated with lipopolysaccharide (LPS)-induced fever in Pekin ducks. 2. LPS, intravenously administered into conscious birds at doses of 1, 10 and 100 microgram kg-1, caused dose-dependent and monophasic increases in body temperature, with fever index values of 3.5, 7.0 and 10.6, respectively. 3. Plasma AVT concentrations also increased with the progression of the fever, with the largest elevation (from 8.4 +/- 1. 6 to 25.2 +/- 3.2 pg ml-1; means +/- s.e.m., n = 7) being caused by the highest dose of LPS. 4. Plasma AII concentrations did not significantly change from basal values (mean of 45.5 +/- 6.3 pg ml-1 for all groups) during the acute phase of the fever response. 5. The osmotic status of the birds, as indicated by plasma osmolality and electrolyte values, did not significantly change in any of the experimental animals. 6. The elevation of AVT in avian fever leads to speculation about a possible antipyretic action of this hormone, which would have particular relevance to understanding the evolution of fever.

Arginine vasotocin gene expression in hypothalamic neurons is up-regulated in chickens drinking hypertonic saline: an in situ hybridization study

Osmotic stress stimulates the release of the avian hypothalamic neuropeptide arginine vasotocin (AVT) into the peripheral circulation. We conducted the present study to investigate the effects of salt-loading on AVT secretion and AVT gene expression in specific hypothalamic nuclei in chickens. White Leghorn chickens were provided food ad lib and either water or 2% NaCl to drink. Both plasma osmolality and plasma AVT levels were significantly increased in chickens that drank 2% NaCl for either two or four days compared to that in chickens that drank water. Results from in situ hybridization analysis demonstrated an increase in the number of neurons expressing AVT mRNA in the supraoptic (SON) and paraventricular nuclei (PVN) in chickens provided 2% NaCl to drink compared to chickens that were provided water to drink. The number of grains per neuron increased in the PVN, but not in the SON of osmotically stimulated birds. Thus, increased osmolality resulting from ingestion of hypertonic saline is an effective stimulus to increase hypothalamic AVT mRNA content in chickens.

Response of broilers to deprivation of food and water for 24 hours

In order to provide information on the state of hydration of broilers during marketing, 7-week-old Ross broilers of mixed sex were kept at 17 or 23 degrees C and deprived of food, or food and water, for 24 h. Measurements were made of live weight, carcass weight, muscle moisture, packed cell volume, plasma glucose, corticosterone, total protein, osmolality and sodium. There was a decrease in live weight, carcass weight, plasma glucose and plasma total protein, and an increase in packed cell volume and corticosterone, in birds deprived of food, or food and water. Muscle moisture increased in birds deprived of food and decreased in birds deprived of food and water. Osmolality decreased in birds deprived of food, the decrease being greater in birds at 23 degrees C. Plasma sodium levels were higher in birds kept at 23 degrees C and increased only in birds deprived of food and water at 23 degrees C.

An in situ hybridization and immunohistochemical study of vasotocin neurons in the hypothalamus of water-deprived chickens

The distribution of immunoreactive vasotocin (IR-AVT) and AVT mRNA in the hypothalamus of White Leghorn cocks was determined by immunohistochemistry and in situ hybridization, respectively. In control birds that were provided with water ad lib, AVT mRNA was distributed in the periventricular and lateral regions of the hypothalamus in clusters of neurons that correspond structurally with the mammalian paraventricular (PVN) and supraoptic (SON) nuclei. Although the distribution of AVT, identified by immunohistochemistry of adjacent serial sections within the hypothalamus, was similar to the distribution of AVT mRNA, the possibility that some positive staining was due to mesotocin neurons was not excluded. Water deprivation for 2 and 4 days resulted in both an increase in levels of AVT mRNA per neuron and the number of AVT mRNA-containing cells. Additionally, water deprivation resulted in a decrease in the amount of IR-AVT per neuron. The results indicate that osmotic stimulation increases AVT gene expression not only in individual neurons but also by activating subpopulation of neurons that are not observed in normally hydrated birds.

Immunoreactive vasotocin in the zebra finch brain (Taeniopygia guttata)

The distribution of vasotocin (VT)-immunoreactive cells and fibers in the zebra finch brain was studied with immunocytochemical techniques. A large number of VT-immunoreactive cells was found in the nucleus preopticus anterior and nucleus paraventricularis. In the lateral parts of the hypothalamus diffusely organized VT-immunoreactive cells were present. Some of these cells were found close to and embedded in the optic tract. An extra-hypothalamic parvocellular cell group was found at the level of the anterior commissure in the dorsal diencephalon. VT-immunoreactive fibers and varicosities were present in a number of extrahypothalamic regions i.e. the septum, the area ventralis of Tsai, the lateral habenula, the optic tectum, the substantia grisea centralis, the nucleus tractus solitarii, the lateral medulla, the nucleus intercollicularis and in the archistriatum surrounding the nucleus robustus archistriatalis. The VT-immunostaining in the lateral septum and dorsal diencephalon showed no sex differences and can not be influenced by testosterone administration.

IN CONCLUSION

the topography of the central VT-immunoreactive network is similar to that in another song bird i.e. the canary; but seasonal and testosterone-dependent changes in VT-immunostaining in the lateral septum and dorsal diencephalon are only observed in the canary.

Alterations in uterine contractility during the oviposition cycle in domestic hens

1. The potencies of several neurohypophysial hormones were examined at different times during the oviposition cycle in an in vitro fowl oxytocic assay. 2. Uterine tissues were removed 2 h before (-2h-OP), immediately after (0h-OP) and 5 h after (+5h-OP) spontaneous oviposition. In addition, uterine tissue was removed immediately after oviposition was induced, by administering prostaglandin E2 2 h before an expected oviposition (Induced-OP). 3. The rank order of oxytocic potencies for the peptides was arginine vasotocin = vasopressin greater than oxytocin greater than mesotocin. The sensitivity of the uterus to the hormones was 0h-OP = Induced-OP greater than -2h-OP = +5-OP. 4. These results suggest that uterine sensitivity to neurohypophysial hormones changes during the oviposition cycle in domestic fowls.

Effect of intrahypothalamic injections of norepinephrine and serotonin on plasma arginine vasotocin and mesotocin in the White Leghorn cockerel

1. Saline (10 microliters), norepinephrine (NE) and Serotonin (5-HT), 500 nmol each, were injected into the anterior third ventricle (A3V; n = 7) or the posterior third ventricle (P3V; n = 11) of ananesthetised, unrestrained White Leghorn cockerels. Plasma arginine vasotocin (AVT) and mesotocin (MT) were measured 20, 60 and 120 min after injection. 2. Injection of NE into both the A3V and P3V had no significant effect on either plasma AVT or plasma MT at any of the sampling times. 3. Administration of 5-HT into the A3V significantly increased plasma MT about two-fold 20 min following injection. At 120 min time, plasma MT returned to normal. 4. In P3V birds, 5-HT had no effect on plasma MT in the first 20 min, but a significant increase in plasma MT occurred 60 to 120 min after injection. The magnitude of the response was lower than in the A3V cockerels. 5. Plasma AVT was not affected by 5-HT administration into the A3V at any of the sampling times, but 5-HT administration into the P3V caused significant rises in plasma AVT at 120 min. 6. Serotonergic, but not noradrenergic, induction of neurohypophysial peptide secretion was demonstrated.

Effects of sex and gonadal steroids on arginine vasotocin and mesotocin in the pineal gland and neurohypophysis of White Leghorn fowls

1. Pineal and neurohypophysial arginine vasotocin (AVT) and mesotocin (MT) were measured in White Leghorn hens, cockerels and castrated males treated with either testosterone propionate (TP) or oestradiol benzoate (EB) (n = 10/group). The lighting regimen was 14 h light: 10 h dark, supplied by natural diffused sunlight and incandescent bulbs. 2. Both AVT and MT were detected in the pineal gland of all the chickens. 3. There was no significant effect of either sex or treatments on pineal MT. 4. Females had about 4 times more pineal AVT than males, regardless of their treatment. There was no effect of the treatments on pineal AVT in the males. 5. No sexual difference in neurohypophysial AVT was detected, but the neurohypophysis of the castrated males treated with EB contained less AVT than the neurohypophysis of the intact males. 6. Intact males had about twice as much MT in the neurohypophysis as females. Castrated males treated with either TP or EB had similar concentrations of neurohypophysial MT, which were lower than that of the intact males, but higher than that of the females.

Arginine vasotocin and mesotocin in the anterior hypothalamus, neurohypophysis, proventriculus and plasma of White Leghorn cockerels, during dehydration

1. The effect of 96 hrs of water deprivation on plasma electrolytes, osmolarity, arginine vasotocin (AVT), mesotocin (MT), and on AVT and MT content in the neurohypophysis, anterior hypothalamic area (AHA) and proventriculus, was studied at 24 hrs intervals, in adult White Leghorn cockerels. 2. Plasma AVT increased three fold during the first 24 hrs but there was no further change during the next 48 hrs. In the last 24 hrs, plasma AVT decreased in about 25%. Plasma MT did not change during the entire period of dehydration. 3. Plasma sodium and osmolarity gradually increased during that time. 4. Neurohypophysial AVT content was depleted by 95% during the period of dehydration while MT content did not change. 5. In the AHA there was no change in AVT levels during dehydration while the levels of MT increased while in the proventriculus there was no change in either AVT or MT levels. 6. For the data collected during the entire experimental period, no correlation was found between plasma osmolarity and plasma AVT, but there was a highly significant negative correlation between plasma osmolarity and neurohypophysial AVT content. 7. It may be suggested that the depletion in AVT content in the neurohypophysis during progressive water deprivation resulted in an insufficient level of AVT in circulation to enable the cockerels to counter the dehydration. This may explain the death of those cockerels which were dehydrated for a further 24 hr period.

Arginine vasotocin and mesotocin levels in theca and granulosa layers of the ovary during the oviposition cycle in hens (Gallus domesticus)

Neurohypophysial hormones in mammals are synthesized by the ovary and may influence reproductive function. Although arginine vasotocin (AVT) can induce premature oviposition in chickens, the gonadal content of AVT or mesotocin (MT) has not been examined in this species. Ovarian follicles were removed 2 hr before oviposition (-2 hr), immediately after oviposition (0 hr), and 5 hr after oviposition (+5 hr). The theca and granulosa layers of the three largest preovulatory and postovulatory follicles were isolated, extracted, and assayed for immunoreactive AVT and MT. AVT content in the theca and granulosa layers was lowest at -2 hr and increased to maximum levels at +5 hr. Pre- and postovulatory follices contained similar amounts of AVT. Maximum AVT levels in the theca and granulosa layers were 2.5 +/- 0.6 and 1.3 +/- 0.2 ng/tissue, respectively. In contrast, theca content of MT was maximal at 0 hr and the highest peptide levels were observed in the largest preovulatory follicle (0.24 +/- 0.02 ng/tissue). The results demonstrate that, compared with circulating levels of the hormones, the ovary of the chicken contains high concentrations of AVT and MT. The ovarian content of AVT and MT varies in a different manner in relation to the oviposition cycle.

Plasma concentrations of arginine vasotocin and mesotocin following pentobarbital anaesthesia and carotid cannulation in domestic fowl

1. Plasma concentrations of arginine vasotocin (AVT) and mesotocin (MT), arterial pH and pCO2, body temperature, respiratory rate, heart rate, mean arterial blood pressure, packed cell volume and plasma osmolality were monitored in birds for 28 h following anaesthesia and carotid cannulation. 2. Plasma MT concentration decreased after 6 h of surgical recovery but there were no differences between 6 and 28 h of recovery. 3. In contrast, plasma AVT concentration was raised only after 27 h, but no differences were observed between 3 and 28 h of recovery. 4. Anaesthesia and/or carotid cannulation apparently suppressed AVT and enhanced MT release, but no significant change in either hormone was observed after 6 h of surgical recovery under the conditions specified in this study.

Control of plasma arginine vasotocin in Kelp gulls (Larus dominicanus): roles of osmolality, volume, and plasma angiotensin II

The physiological roles of plasma osmolality, volume, and angiotensin II (AII) in the control of plasma arginine vasotocin (AVT) have been evaluated in the Kelp gull. Plasma AVT (measured by radioimmunoassay) consistently followed the changes in plasma osmolality induced by dehydration, intravenous (iv) infusion of hypertonic saline, or iv infusion of hypotonic glucose solution. Osmoreceptor control of AVT was further characterized by the stimulatory effect of iv hypertonic mannitol but lack of effect of iv hypertonic urea. A direct volume effect on AVT release was demonstrated during hemorrhage, but blood volume reductions in excess of 10% were required. However, the volume of the extracellular fluid (ECF) compartment does have an important role in modulating the osmotic release of AVT in a way that enables contraction or expansion of ECF to be more expeditiously corrected than would occur if osmoreceptors alone regulated plasma AVT. Any physiological role of plasma AII in the control of plasma AVT is doubtful because after the iv infusion of AII for 60 min at 10, 25, 50, and 100 ng.min-1, only the two highest doses of AII, which produced supraphysiological plasma AII levels, caused elevations of plasma AVT. In addition, the osmotic reactivity of AVT release was not altered by exogenous administration of AII.

Increased levels of arginine vasotocin and neurophysin during nesting in sea turtles

Arginine vasotocin (AVT) and neurophysin (NP) levels were measured by radioimmunoassay in two species of sea turtle, the olive ridley, Lepidochelys olivacea, and the loggerhead, Caretta caretta, during the brief period of nesting and oviposition. In both species, AVT was low in animals which were not reproductively active. AVT was also low at the time animals emerged from the surf to nest, but increased significantly during oviposition and then declined as the animals returned to the water. NP increased in concert with AVT, also reaching highest levels during oviposition. In both species, however, NP levels remained elevated over prenesting levels at the time of return to the water. These findings are consistent with the hypothesis that an AVT-neurophysin complex is released from the neurohypophysis during nesting, and that AVT is a physiological regulator of oviducal contractions in sea turtles.

Effect of heat stress on plasma levels of arginine vasotocin and mesotocin in domestic fowl (Gallus domesticus)

1. The effect of an acute heat stress on plasma arginine vasotocin (AVT) and mesotocin (MT) levels were determined in non-heat-acclimated domestic fowl. 2. Heat increased (P less than 0.05) AVT and decreased MT (P less than 0.05) levels but had no affect on plasma osmolality. Changes in MT were correlated with body temperature (-0.40) and blood pCO2 (0.32). However, changes in AVT were not correlated with any physiological variable, including MT. 3. During thermoneutral recovery, with the exception of hematocrit which remained lower (P less than 0.05), all monitored variables returned to values which were not different (P greater than 0.05) from those observed prior to heat stress. 4. These results indicate that in non-heat-acclimated birds, acute heat stress elevated plasma AVT and suppressed the release of MT and that changes in these hormones occurred independent of any change in plasma osmolality.

Physiological effects of arginine vasotocin and mesotocin in cockerels

1. The effects of continuous infusion of 0.1, 1.0 and 10.0 mU/min/kg body weight of arginine vasotocin (AVT) or mesotocin (MT) on cardiovascular and thermoregulatory responses, on plasma osmolality and ionic composition and on plasma concentrations of AVT, MT, prolactin and aldosterone, were investigated in conscious White Leghorn cockerels. 2. Neither of the peptides, at any dose, affected cardiovascular functions, plasma ions and osmolality. Infusion of MT at the rate of 10 mU/min/kg body weight increased respiratory rate. Both peptides at doses of 1 and 10 mU/min/kg reduced the temperatures of the comb and shank but had no effect on the skin and cloaca. 3. Doses of 0.1 and 1.0 mU MT/min/kg reduced plasma aldosterone and at 10 mU/min/kg increased plasma AVT. At any given dose MT had no effect on plasma prolactin. AVT at 0.1 and 1.0 mU/min/kg of AVT reduced plasma MT. AVT at 1.0 mU/min/kg increased plasma prolactin and at 10 mU/min/kg reduced plasma aldosterone. 4. During saline infusion, plasma MT was positively correlated with plasma AVT and negatively correlated with respiratory rate and cloacal temperature. Plasma AVT showed a positive correlation with plasma MT and aldosterone and a negative correlation with respiratory rate and skin temperature. 5. During saline infusion, there was no significant correlation between cardiovascular functions, or plasma osmolality and ionic composition and plasma MT or AVT. 6. The present study suggests that interrelationships between circulating concentrations of AVT and MT do exist and that AVT affects aldosterone secretion. These neurohypophysical peptides are involved in thermoregulation.

Plasma arginine vasotocin and angiotensin II in the water deprived Kelp gull (Larus dominicanus), Cape gannet (Sula capensis) and Jackass penguin (Spheniscus demersus)

1. The basal levels of the osmoregulatory hormones, arginine vasotocin (AVT) and angiotensin II (AII) were measured (by radioimmunoassay) in the plasma of conscious Kelp gulls, Cape gannets and Jackass penguins. 2. The responses of the hormones to similar degrees of hypertonicity and hypovolemia caused by water deprivation have also been determined. 3. Dehydration elevated plasma AVT and plasma AII in all three species. 4. The AVT concentration was increased by 2-4 fold and although in each case the correlation between plasma osmolality and plasma AVT was highly significant (2P less than 0.01), the sensitivity of release was greater in the gull (1.13 pg/ml per mOsm/kg) than in the gannet (0.36 pg/ml per mOsm/kg) or penguin (0.44 pg/ml per mOsm/kg). 5. Dehydration increased plasma AII 3-fold in the three bird types.

Interrelationship between arginine vasotocin, prostaglandin, and uterine contractility in the control of oviposition in the hen (Gallus domesticus)

Uterine electromyographic activity (EMG), plasma concentrations of prostaglandin (PG) F and E, and arginine vasotocin (AVT) were simultaneously measured in relation to PGE2-induced premature oviposition and to indomethacin-blocked oviposition in chickens. The administration of indomethacin (5 mg, im) 3 hr before the predicted time of oviposition delayed egg lay by 8-14 hr, whereas control hens laid eggs at the predicted time. In indomethacin-treated hens increases in uterine EMG activity and plasma concentrations of PGF, PGE, and AVT were not observed at the expected time of oviposition, whereas a marked increase in plasma PGF and AVT occurred during spontaneous oviposition. The intrauterine administration of PGE2 (1 microgram) 3 hr before predicted oviposition induced premature egg lay within 5 min. Premature oviposition was accompanied by significant elevations in both uterine EMG activity and plasma levels of AVT. Changes in plasma levels of PGF and PGE were not observed. When premature oviposition was induced, significant increases in EMG activity and plasma concentrations of PGF and AVT were observed at the expected time of oviposition in the absence of an egg in the uterus. The administration of PGE2 at the predicted time of oviposition in hens pretreated with indomethacin induced oviposition which was accompanied by a significant increase in plasma AVT levels. The results suggest that AVT release is stimulated by uterine contractility in chickens.

Arginine vasotocin (AVT) release in relation to uterine contractility in the hen

The relationship between plasma levels of arginine vasotocin (AVT) and factors associated with increases in uterine contractility was studied in the domestic hen. Plasma AVT levels increased from 3.3 +/- 0.3 microU/ml 15 min before a midsequence oviposition (OP) to 14.8 +/- 0.6 microU/ml at OP and then decreased to 5.2 +/- 0.6 microU/ml 15 min following OP. A ninefold increase in plasma AVT concentration was observed in hens laying a terminal egg of a sequence, which is not immediately followed by ovulation (OV). AVT levels also increased approximately 1 hr before the time of the first ovulation (C1OV) of the next sequence in association with an increase in uterine contractility. When OP was induced 2 hr before an expected OP by intrauterine administration of prostaglandin F2 alpha (PGF2 alpha, 1.0 microgram), plasma AVT levels immediately increased threefold (P less than 0.001) and then returned to basal levels within 30 min. In PGF2 alpha-treated hens AVT levels rose at the expected time of OP (P less than 0.05) in association with an increase in uterine contractility without OP actually occurring. When C1OV was induced by LH-RH (25 micrograms, iv), a small but significant increase of AVT similar to levels during spontaneous C1OV was observed. These results suggest that plasma AVT levels increase with every ovulation and oviposition in the absence of an egg in the uterus and that AVT is released in association with induced ovulation and oviposition.

Osmotic stimuli and NaCl-intake in the fowl; release of arginine vasotocin and prolactin

White Plymouth Rock hens were fed a high- and a low-NaCl content of the diet. The two groups were exposed to moderate dehydration, to intra-arterial hyperosmotic NaCl-loading, or to injection of physiological doses of arginine vasotocin (AVT). The plasma levels of AVT and prolactin were measured by accurate and sensitive radioimmunoassay and the osmolality and Na, K (and Cl) concentrations also measured for 48 h after dehydration, and for 60-90 min after NaCl-loading or AVT-injection. The plasma concentration of AVT after a given increase of plasma osmolality was in all experiments found higher in the low- as compared to the high-NaCl diet group. The average difference was 0.2 pg/ml X mOsm. The intra-arterial injection of AVT resulted in a strictly mono-exponential fall over the next hour with an average half-life of 6.3 min without any difference between the high- and the low-NaCl diet groups. It is concluded (a) that the release of prolactin after osmotic stimulation is most likely caused by a direct effect of osmolality (or Na concentration) and not by AVT, (b) that the release of AVT is influenced by the NaCl-intake in a direction which tends to maintain extracellular volume.

Haemorrhage and adrenocortical activity in the fowl (Gallus domesticus)

Plasma aldosterone concentrations were markedly elevated in chickens by the removal of 10-30% of their total blood volume. This aldosterone response to haemorrhage was delayed and of reduced magnitude in birds pretreated for 48 hr with dexamethasone (100 micrograms/kg every 12 hr), in which the basal aldosterone level was also suppressed. Corticosterone concentrations were elevated in both haemorrhaged and nonhaemorrhaged birds, although these responses were completely abolished by dexamethasone pretreatment, which also reduced the basal corticosterone concentration. Prolactin concentrations were unaffected by haemorrhage. These results demonstrate that haemorrhage specifically affects adrenocortical function by increasing aldosterone release and suggests that factors other than the pituitary-adrenal axis are responsible for this stimulation of secretion.