Evidence for the presence of arginine vasotocin (8-arginine oxytocin) and oxytocin in neurohypophyseal extracts from amphibians and reptiles

Egg Removal via Cloacoscopy in Three Dystocic Leopard Geckos (Eublepharis macularius)

Dystocia is a multifactorial, life-threatening condition commonly affecting pet reptiles. Treatment for dystocia can be either medical or surgical. Medical treatment usually involves the administration of oxytocin, but in some species or, in some cases, this treatment does not work as expected. Surgical treatments such as ovariectomy or ovariosalpingectomy are resolutive, but invasive in small-sized reptiles. In this paper, we describe three cases of post ovulatory egg retention in three leopard geckos (Eublepharis macularius) successfully treated through a cloacoscopic removal of the retained eggs, after a non resolutive medical treatment. The intervention was fast, non-invasive, and no procedure-related adverse effects were noted. The problem relapsed six months later in one animal, and a successful bilateral ovariosalpingectomy was performed. Cloacoscopy should be considered a valuable, non-invasive tool for egg removal in dystocic leopard geckos when the egg is accessible to manipulation. Recrudescence or complications such as adhesions, oviductal rupture, or the presence of ectopic eggs should recommend surgical intervention.

Stress, health and the welfare of laying hens

It is essential to understand responses to stress and the impact of stress on physiological and behavioural functioning of hens, so as to assess their welfare. The current understanding of stress in laying hens is comprehensively reviewed here. Most research on stress in hens has focussed on the activity of the adrenal glands, with the most common approach being to measure corticosterone, which is the predominant glucocorticoid produced by birds in response to stress. While these measures are useful, there is a need to understand how the brain regulates stress responses in hens. A greater understanding of the sympathoadrenal system and its interaction with the hypothalamo–pituitary–adrenal axis is required. There is also a lack of knowledge about the many other peptides and regulatory systems involved in stress responses in hens. The usefulness of understanding stress in hens in terms of assessing welfare depends on appreciating that different stressors elicit different responses and that there are often differences in responses to, and impacts of, acute and chronic stress. It is also important to establish the actions and fate of stress hormones within target tissues. It is the consequences of these actions that are important to welfare. A range of other measures has been used to assess stress in hens, including a ratio of heterophils to lymphocytes and haematocrit:packed cell-volume ratio and measures of corticosterone or its metabolites in eggs, excreta, feathers and the secretions of the uropygial gland. Measures in eggs have proffered varying results while measures in feathers may be useful to assess chronic stress. There are various studies in laying hens to indicate impacts of stress on the immune system, health, metabolism, appetite, and the quality of egg production, but, generally, these are limited, variable and are influenced by the management system, environment, genetic selection, type of stressor and whether or not the birds are subjected to acute or chronic stress. Further research to understand the regulation of stress responses and the impact of stress on normal functioning of hens will provide important advances in the assessment of stress and, in turn, the assessment of welfare of laying hens.

Oral administration of D-aspartate, but not L-aspartate, depresses rectal temperature and alters plasma metabolites in chicks

AIMS

L-Aspartate (L-Asp) and D-aspartate (D-Asp) are physiologically important amino acids in mammals and birds. However, the functions of these amino acids have not yet been fully understood. In this study, we therefore examined the effects of L-Asp and D-Asp in terms of regulating body temperature, plasma metabolites and catecholamines in chicks.

MAIN METHODS

Chicks were first orally administered with different doses (0, 3.75, 7.5 and 15 mmol/kg body weight) of L- or D-Asp to monitor the effects of these amino acids on rectal temperature during 120 min of the experimental period.

KEY FINDINGS

Oral administration of D-Asp, but not of L-Asp, linearly decreased the rectal temperature in chicks. Importantly, orally administered D-Asp led to a significant reduction in body temperature in chicks even under high ambient temperature (HT) conditions. However, centrally administered D-Asp did not significantly influence the body temperature in chicks. As for plasma metabolites and catecholamines, orally administered D-Asp led to decreased triacylglycerol and uric acid concentrations and increased glucose and chlorine concentrations but did not alter plasma catecholamines.

SIGNIFICANCE

These results suggest that oral administration of D-Asp may play a potent role in reducing body temperature under both normal and HT conditions. The alteration of plasma metabolites further indicates that D-Asp may contribute to the regulation of metabolic activity in chicks.

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.

Plasma aldosterone, angiotensin II, and arginine vasotocin concentrations in the toad, Bufo marinus, following osmotic treatments

To clarify the physiological roles of the renin-angiotensin-aldosterone system (RAAS) and arginine vasotocin (AVT) on body fluid regulation in amphibians, we measured plasma concentrations of aldosterone (ALDO), angiotensin II (ANG II), and AVT after various osmotic challenges in the marine toad, Bufo marinus (Bufonidae). Hematocrit value (Ht) as an indicator of plasma volume, plasma osmolality and concentrations of plasma components (Na(+), Cl(-), K(+), and urea) were also measured. The toads were maintained under various osmotic treatments for 7 days. In dehydrated toads, plasma concentrations of ALDO, ANG II, AVT, and all plasma components measured were increased. In toads maintained in 300 mosmol/kg H(2)O NaCl solution, plasma osmolality, Na(+), Cl(-), urea, and plasma AVT concentrations were significantly increased, and Ht and plasma concentrations of ALDO and ANG II were significantly decreased. In toads maintained in tap water, plasma osmolality, and concentrations of Na(+) and ALDO were significantly decreased. We also estimated total body water (TBW), plasma volume (PV) using Evans Blue dye and Ht in the toads under various osmotic treatments. In dehydrated toads, TBW and PV were significantly decreased and Ht was significantly increased in comparison with those of control. In toads maintained in 300 mosmol/kg H(2)O NaCl solution, TBW and PV were significantly increased and Ht was significantly decreased in comparison with those of control. There was a significant negative correlation between Ht and PV or TBW. These results show that dehydration, which induces hypovolemic and hyperosmotic conditions, stimulates increases of plasma ALDO, ANG II, and AVT concentrations, while hypervolemic treatment induces decreases of plasma ALDO and ANG II concentrations. There were significant correlations between plasma osmolality and AVT concentration, between Ht and concentrations of RAAS hormones, and between plasma concentrations of ALDO and ANG II. These results suggest that volumetric and osmometric systems regulated by RAAS hormones and AVT are present in B. marinus.

Effect of neurohypophysial hormones on fluid movement across isolated bladder of Rana cancrivora, Rana temporaria and Bufo melanostictus

1. The rate of fluid movement across the wall of isolated amphibian urinary bladder was estimated using hemi-bladders of the tropical euryhaline Rana cancrivora, the temperate R. temporaria and the tropical Bufo melanostictus.2. The rate of water outflow across the bladder walls was: Rana cancrivora, 4.8 mul./cm(2).hr; R. temporaria, 7.2 mul./cm(2).hr; Bufo melanostictus, 3.7 mul./cm(2).hr.3. When neurohypophysial peptides were added to the serosal solution the rates of water outflow were increased; dose-response curves were prepared relating the augmented rate of fluid movement to the concentration in the bathing fluid of vasopressin, oxytocin or vasotocin.4. The potencies of the peptides in respect of bladders of each species were:Vasopressin, B. melanostictus:Rana temporaria:R. cancrivora, 500:20:1.Oxytocin, R. temporaria:B. melanostictus:Rana cancrivora, 100:5:1.5. The ratio of sensitivity of the bladder of each species to the presence of the different peptides was:R. cancrivora, vasotocin:oxytocin:vasopressin, 1000:5:1.R. temporaria, oxytocin:vasopressin, 15:1. Bufo melanostictus, oxytocin:vasopressin, 1:30.6. The effect of extract of the pituitary gland of Rana cancrivora was examined on R. cancrivora bladder. It had a dose-response curve similar to the dose-response curve of vasotocin.7. The vasotocin content of the pituitary gland of R. cancrivora was estimated(a) from the dose-response curves using R. cancrivora bladder,(b) by a three-point assay using R. cancrivora bladder and(c) by its effect on water uptake across the skin of Bufo melanostictus. One pituitary gland of Rana cancrivora was found to contain about 0.1 mug vasotocin.8. The urinary bladder of R. cancrivora was less responsive to neurohypophysial peptides than the bladder of R. temporaria or Bufo melanostictus.9. The hormonal content of the pituitary gland of Rana cancrivora was smaller than that found in other amphibians.