Relationships between renal hemodynamics and plasma levels of arginine vasotocin and mesotocin during hemorrhage in the domestic fowl (Gallus domesticus)

Laboratory Evaluation of Renal Function in Birds

Renal disease often remains undetected in living patients. Urinalysis might contribute to the diagnosis of some kinds of renal and metabolic diseases. Blood uric acid concentrations reflect the excretory functional capacity of the renal proximal tubules. In contrast, blood urea concentrations are significantly affected by the bird's hydration status and have been proposed as a useful variable to detect prerenal causes for renal impairment in birds. Measurement of exogenous creatinine excretion shows promising preliminary results to become a useful test for the assessment of renal excretion in birds.

Effects of nest-deprivation on hypothalamic mesotocin in incubating native Thai hens (Gallus domesticus)

Avian mesotocin (MT) is homologous to oxytocin in mammals. Native Thai chickens (Gallus domesticus) strongly express maternal behaviors including incubation and rearing. However, the role of MT during incubation behavior has never been studied. The objective of this study was to determine the physiological function(s) of the MTergic system in incubation behavior in native Thai chickens. The brains were collected from incubating (INC) and nest-deprived (ND) hens at different time points (days 3, 6, 8, 10, 14, 18, and 21; n=6). Immunohistochemistry technique was used to compare the numbers of MT-immunoreactive (-ir) neurons between the INC and ND hens within the Nucleus supraopticus, pars ventralis (SOv), Nucleus preopticus medialis (POM), and Nucleus paraventricularis magnocellularis (PVN). The results revealed that the numbers of MT-ir neurons within the SOv, POM, and PVN remained high during the incubating stage. The number of MT-ir neurons in the SOv was lower than that of the POM and PVN. Disruption of incubation behavior by nest deprivation caused the numbers of MT-ir neurons within the SOv, POM, and PVN to decrease throughout the observation periods. For the first time, this study demonstrates that the MTergic system within the SOv, POM, and PVN may be involved with incubation behavior. In addition, these results further suggest that the MTergic neurons in these nuclei are not only regulated by rearing behavior but also might have a role in the initiation and maintenance of incubation behavior in this tropical species.

A possible mechanism contributing to the synergistic action of vasotocin (VT) and corticotropin-releasing hormone (CRH) receptors on corticosterone release in birds

Arginine vasotocin (AVT) and corticotropin-releasing hormone (CRH) are two neuronal regulators in the hypothalamic-pituitary-adrenal (HPA) axis that modulate biological responses to stress in avian species. When AVT and CRH are administered together in vitro or in vivo, levels of adrenocorticotropic hormone (ACTH) or plasma corticosterone (CORT) are released, respectively, in a synergistic manner. The underlying mechanism of this greater than additive stress response was investigated by expressing the vasotocin receptor type 2 (VT2R) and CRH receptor type 1 (CRH-R1), both G-protein coupled receptors, in HeLa cells. Fluorescence resonance energy transfer (FRET) analysis provided the evidence for heterodimerization of the VT2R/CRH-R1 in the presence of their respective ligands, AVT and CRH. The VT2R and CRH-R1 were tagged at the C-terminal ends with either cyan fluorescent protein (CFP) or yellow fluorescent protein (YFP), and a VT2R chimera was constructed by replacing the fourth transmembrane region (TM4) of the VT2R with TM-IV of the β2-adrenergic receptor (β2AR). When VT2R/β2AR chimera and CRH-R1 were expressed in HeLa cells, heterodimerization was partly disrupted. Taken together, these data indicate that TM-IV of the VT2R may provide an important interface for effective receptor dimerization, suggesting that direct molecular interaction between VT2R and CRH-R1 receptors plays a role in mediating an enhanced interaction between these two receptors. Their interaction at the anterior pituitary level may potentiate the endocrine output of the avian HPA system.

Mesotocin and maternal care of chicks in native Thai hens (Gallus domesticus)

Oxytocin (OT) is known to induce and regulate maternal behaviors in mammals via the supraoptic nucleus and paraventricular nucleus (PVN), whereas the function of mesotocin (MT; the avian homolog of OT) is poorly understood in birds. To elucidate the association of MT and the regulation of maternal behaviors in birds, we studied changes in the number of MT-immunoreactive (ir) neurons in native Thai chickens using immunohistochemistry. We observed that MT-ir neurons and fibers appeared in discrete regions located close to the third ventricle from the level of the preoptic area through the anterior hypothalamus with an abundance observed in the nucleus supraopticus, pars ventralis (SOv), nucleus preopticus medialis (POM), and PVN. The number of MT-ir neurons was low in the SOv, POM, and PVN of non-laying hens, but it increased gradually when the hens entered the laying stage, and peaked in incubating and rearing hens. We compared the number of MT-ir neurons in the SOv, POM, and PVN of native Thai hens rearing chicks (R) with that of non-rearing chicks (NR). The number of MT-ir neurons was high in the R hens, but low in the NR hens in these nuclei. For the first time, these results indicate that the association between the MT neurons and the presence of chicks might, in part, play a role in the neuroendocrine reorganization to establish and maintain maternal behaviors in native Thai chickens. MTergic activity is likely related to the contribution of rearing behavior in this equatorial precocial species.

Dopamine and mesotocin neurotransmission during the transition from incubation to brooding in the turkey

We investigated the neuroendocrine changes involved in the transition from incubating eggs to brooding of the young in turkeys. Numbers of mesotocin (MT; the avian analog of mammalian oxytocin) immunoreactive (ir) neurons were higher in the nucleus paraventricularis magnocellularis (PVN) and nucleus supraopticus, pars ventralis (SOv) of late stage incubating hens compared to the layers. When incubating and laying hens were presented with poults, all incubating hens displayed brooding behavior. c-fos mRNA expression was found in several brain areas in brooding hens. The majority of c-fos mRNA expression by MT-ir neurons was observed in the PVN and SOv while the majority of c-fos mRNA expression in dopaminergic (DAergic) neurons was observed in the ventral part of the nucleus preopticus medialis (POM). Following intracerebroventricular injection of DA or oxytocin (OT) receptor antagonists, hens incubating eggs were introduced to poults. Over 80% of those injected with vehicle or the D1 DA receptor antagonist brooded poults, while over 80% of those receiving the D2 DA receptor antagonist or the OT receptor antagonist failed to brood the poults. The D2 DA/OT antagonist groups also displayed less c-fos mRNA in the dorsal part of POM and the medial part of the bed nucleus of the stria terminalis (BSTM) areas than did the D1 DA/vehicle groups. These data indicate that numerous brain areas are activated when incubating hens initially transition to poult brooding behavior. They also indicate that DAergic, through its D2 receptor, and MTergic systems may play a role in regulating brooding behaviors in birds.

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.

Renal responses of normal and preascitic broilers to systemic hypotension induced by unilateral pulmonary artery occlusion

During the pathophysiological progression of pulmonary hypertension syndrome (PHS; ascites), broilers concurrently develop systemic hypotension (low mean systemic arterial pressure) that may initiate renal retention of water and solute, contributing to fluid accumulation in the abdominal cavity (ascites). In male Single Comb White Leghorns, glomerular filtration is autoregulated over a systemic arterial pressure range of 110 to 60 mm Hg, and corresponding reductions in urine flow are attributed to a phenomenon known as pressure natriuresis. Acute unilateral pulmonary artery occlusion was used in the present study to reduce systemic arterial pressure toward the lower autoregulatory limit for glomerular filtration, and to evaluate kidney function in normal and preascitic broilers. Preascitic broilers characteristically exhibited lower (P < or = 0.05) values for mean systemic arterial pressure (91 vs 100 mm Hg) and percentage saturation of hemoglobin with oxygen (73 vs 84%), higher hematocrits (35 vs 30%), heavier right ventricles (3.44 vs 2.32 g), and higher right:total ventricular weight ratios (0.32 vs 0.24) than normal broilers. Body weights (2,445 vs 2,429 g, respectively), left ventricle plus septum weights (7.16 vs 7.19 g), and heart rates (349 vs 341 beats/min) were similar. Preascitic broilers exhibited larger (P < or = 0.05) dependent reductions in glomerular filtration, urine flow, osmolal clearance, and solute excretion and had a higher free water clearance than normal broilers in response to pulmonary artery occlusion. The differences observed between normal and preascitic broilers demonstrate that systemic hypotension can trigger renal mechanisms contributing to fluid and solute retention during development of PHS.

Arginine vasotocin gene expression and secretion during osmotic stimulation and hemorrhagic hypotension in hens

In chickens, hyperosmolality stimulates the secretion of vasotocin (AVT) and up-regulates hypothalamic AVT gene expression. Hemorrhage, on the other hand, has not been considered an effective stimulus for AVT release in this species. The effects of acute osmotic stress and prolonged hemorrhagic hypotension on AVT gene expression and secretion were studied in White Leghorn hens. Conscious hens were osmotically stimulated by administering a single ip injection of 3 M NaCl (5 ml/kg). Urethane-anesthetized hens were bled to a mean arterial pressure of 80-90 mm Hg and the pressure was maintained within this range by additional bleeding. A total of about 30% of the estimated blood volume was removed. Both experiments were terminated after 1 hr of stimulation. Plasma AVT levels in the hyperosmotic and hypovolemic hens were 4- and 2-fold higher, respectively, compared to controls. Hypothalamic AVT mRNA levels, detected by Northern blot analysis, were 2.5- and 2-fold higher in the osmotically stimulated and hypotensive groups, respectively, compared to control groups. As determined by in situ hybridization, both osmotic stimulation and hypovolemia resulted in an increase in the number of AVT mRNA-containing neurons in the supra-optic and paraventricular nuclei. Our results indicate that, under the conditions used, hypotension and hyperosmolality are equally effective in stimulating AVT gene expression and secretion of AVT.

Arginine vasotocin gene expression in neuroendocrine, reproductive and gastrointestinal tissues of the domestic fowl: detection by reverse transcriptase polymerase chain reaction

Arginine vasotocin gene transcripts in various tissues of the domestic fowl were detected by reverse transcriptase polymerase chain reaction followed by Southern blot analysis using a 209 bp fragment from the 3'-region of a cDNA encoding chicken arginine vasotocin as the probe. Relatively strong signals were observed with hypothalamic, adenohypophysial and proventricular RNA as the starting material. Lesser signals were obtained from RNA isolated from shell gland, adrenal gland, post-ovulatory follicles and ovarian thecal cells. Arginine vasotocin gene transcripts were undetectable in the posterior pituitary gland, small intestine and large intestine. These results suggest that in addition to its well-known antidiuretic and oxytocic actions, arginine vasotocin may act as a local neuromodulator or mediator and have other important autocrine or paracrine actions in non-hypothalamic tissues.

Aflatoxin and glutathione in domestic fowl (Gallus domesticus)—II. Effects on hepatic blood flow

1. The effect of aflatoxin on plasma aspartate aminotransferase (AST), protein, and hepatic glutathione (GSH) and hepatic blood flow (perfusion), were determined in 3-week-old male chickens. 2. Daily aflatoxin gavage (2 mg/kg body wt, in corn oil) for 5 and 10 days elevated plasma AST and hepatic GSH, and depressed plasma protein and hepatic perfusion. Also, renal GSH was elevated after 10 days of aflatoxin treatment. 3. Birds given aflatoxin for 10 days followed by a 10-day recovery period exhibited tissue GSH, plasma AST and protein levels that were not different from control, but hepatic perfusion remained depressed.

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.

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.

Effect of hemorrhage on hepatic tissue blood flow in the domestic fowl (Gallus domesticus)

1. Thermal Pulse Decay (TPD) methodology was used to monitor hepatic tissue blood flow (hepatic perfusion) in anesthetized birds prior to and during hemorrhagic hypotension. 2. Hemorrhage was accomplished by periodic removal of blood through a carotid cannula. Reducing the estimated blood volume (BV) from 100 to less than 50% decreased hepatic perfusion from 4.36 +/- 0.7 to 1.88 +/- 0.7 ml/min/g. 3. Changes in hepatic perfusion during the experiment were related to mean arterial blood pressure (MABP) by the following linear regression equation: hepatic perfusion = -1.79 +/- 0.0807x (r2 = 0.57).