Liver Na+K+-ATPase activity and circulating levels of corticosterone and thyroid hormones following cold and heat exposure in the pigeon

Oral administration of L-citrulline changes the concentrations of plasma hormones and biochemical profile in heat-exposed broilers

We examined the effects of oral administration of L-citrulline (L-Cit) on plasma metabolic hormones and biochemical profile in broilers. Food intake, water intake, and body temperature were also analyzed. After dual oral administration (20 mmol/head/administration) of L-Cit, broilers were exposed to a high ambient temperature (HT; 30 ± 1°C) chamber for 120 min. Oral administration of L-Cit reduced (p < .001) rectal temperature in broilers. Food intake was increased (p < .05) by heat stress, but it was reduced (p < .05) by L-Cit. Plasma levels of 3,5,3'-triiodothyronine, which initially increased (p < .0001) due to heat stress, were reduced (p < .01) by oral administration of L-Cit. Plasma insulin levels were increased by heat exposure (p < .01) and oral L-Cit (p < .05). Heat stress caused a decline (p < .05) in plasma thyroxine. Plasma lactic acid (p < .05) and non-esterified fatty acids (p < .01) were increased in L-Cit-treated heat-exposed broilers. In conclusion, our results suggest that oral L-Cit can modulate plasma concentrations of major metabolic hormones and reduces food intake in broilers.

The role of glucocorticoids in the vertebrate response to weather

Changes in the environment related to inclement weather can threaten survival and reproductive success both through direct adverse exposure and indirectly by decreasing food availability. Glucocorticoids, released during activation of the hypothalamic-pituitary-adrenal axis as part of the stress response, are an important candidate for linking vertebrate coping mechanisms to weather. This review attempts to determine if there is a consensus response of glucocorticoids to exposure to weather-related stimuli, including food availability, precipitation, temperature and barometric pressure. The included studies cover field and laboratory studies for all vertebrate taxa, and are separated into four exposure periods, e.g., hours, days, weeks and months. Each reported result was assigned a score based on the glucocorticoid response, e.g., increased, no change, or decreased. Short-term exposure to weather-related stimuli, of up to 24 h, is generally associated with increased glucocorticoids (79% of studies), suggesting that these stimuli are perceived as stressors by most animals. In contrast, the pattern for exposures longer than 24 h shows more variation, even though a majority of studies still report an increase (64%). Lack of glucocorticoid increases appeared to result from instances where: (1) prolonged exposure was a predictable part of the life history of an animal; (2) environmental context was important for the ultimate effect of a stimulus (e.g., precipitation limited food availability in one environment, but increased food in another); (3) prolonged exposure induced chronic stress; and (4) long-term responses appeared to reflect adaptations to seasonal shifts, instead of to short-term weather. However, there is a strong bias towards studies in domesticated laboratory species and wild animals held in captivity, indicating a need for field studies, especially in reptiles and amphibians. In conclusion, the accumulated literature supports the hypothesis that glucocorticoids can serve as the physiological mechanism promoting fitness during inclement weather.

Endocrine consequences of an acute stress under different thermal conditions: A study of corticosterone, prolactin, and thyroid hormones in the pigeon (Columbia livia)

In the context of global change, the physiological and hormonal stress responses have received much attention because of their implications in terms of allostasis. However, most studies have focused on glucocorticoids only as the "common" response to stressors while neglecting other endocrine axes and hormones (e.g. prolactin, thyroid hormones) that play a crucial role in metabolic adjustments. Interestingly, the responsiveness of all these endocrine axes to stress may depend on the energetic context and this context-dependent stress response has been overlooked so far. In the wild, temperature can vary to a large extent within a short time window and ambient temperature may affect these metabolic-related endocrine axes, and potentially, their responsiveness to an acute stressor. Here, we explicitly tested this hypothesis by examining the effect of a standardized stress protocol on multiple hormonal responses in the rock pigeon (Columbia livia). We tested the effect of an acute restraint stress on (1) corticosterone levels, (2) prolactin levels, and (3) thyroid hormone levels (triiodothyronine, thyroxine) in pigeons that were held either at cool temperature (experimental birds) or at room temperature (control birds) during the stress protocol. Although we found a significant influence of restraint stress on most hormone levels (corticosterone, prolactin, and thyroxine), triiodothyronine levels were not affected by the restraint stress. This demonstrates that stressors can have significant impact on multiple endocrine mechanisms. Importantly, all of these hormonal responses to stress were not affected by temperature, demonstrating that the exposure to cold temperature does not affect the way these hormone levels change in response to handling stress. This suggests that some endocrine responses to temperature decreases may be overridden by the endocrine responses to an acute restraint stress.

Vitamin E supplementation reduces dexamethasone-induced oxidative stress in chicken semen

1. We examined the effects of supplemental dietary vitamin E (Vit E) on semen quality and antioxidative status in male domestic fowls exposed to oxidative stress induced by synthetic glucocorticoid, dexamethasone (DEX) injection. 2. Thirty-six Egyptian local cross males, 42 weeks old, were housed individually in cages in an open-sided building under 16 h light:8 h dark and were provided with commercial feed and water ad libitum. Birds were divided into 4 groups: DEX (4 mg/bird/d), Vit E (200 mg/kg diet), DEX + Vit E (4 mg/bird/d + 200 mg/kg diet, respectively) and control, n = 9. All treatments lasted for 7 continuous days. 3. Oxidative stress induced by injection of DEX (4 mg/bird/d) resulted in decreased sperm count and motility correlated with an increased percentage of dead sperms. Vit E (200 mg/kg diet) enhanced sperm count and viability when supplemented to stress-induced birds, compared to DEX treatment alone. 4. In seminal plasma, low calcium concentration, high lipid peroxidation and reduced activity of glutathione peroxidase were associated with the oxidative stress. Vit E reduced lipid peroxidation in the seminal plasma. 5. In conclusion, excessive supplemental dietary Vit E improved semen quality when cockerels were subjected to stress conditions. It increased both sperm count and motility, reduced the percentage of dead sperm and enhanced the antioxidative status of seminal plasma.

Effect of cold acclimation on oxidative capacity and respiratory properties of liver and muscle mitochondria in ducklings, Cairina moschata

1. The effect of cold acclimation on the oxidative capacity of the skeletal muscle (gastrocnemius and pectoralis) and the liver of ducklings was investigated. 2. In cold-acclimated (CA) ducklings, the oxidative capacity of the liver was higher (+40%) than in ducklings reared at thermoneutraility (TN). In these animals an increase in state 4 respiration and a decrease in the respiratory control index (RCI) was also found. 3. The oxidative capacity of both pectoralis and gastrocnemius muscles also increased in CA animals. 4. In these muscles the oxidatibe capacity of the subsarcolemmal mitochrondrial fraction of CA ducklings was higher (+96% in the gastrocnemius and +58% in the pectoralis) than the intermyofibrillar one (+51% in the gastrocnemius and +33% in the pectoralis). No variations were observed in either the RCI or the ADP/O ratios. 5. These findings indicate that the energy expenditure needed for non-shivering thermogenesis (NST) in cold-acclimated ducklings can be met by the increase in the oxidative capacity of the skeletal muscle and the liver, each by different mechanisms; the gastrocnemius muscle would seem to play a prominent role.

Influence of corticosterone infusion on plasma levels of catecholamines, thyroid hormones, and certain metabolites in laying hens

Corticosterone was infused continuously through subcutaneously implanted mini-osmotic pumps into laying White Leghorn hens at the rate of 30 micrograms/hr for 14 or 28 days. In both groups receiving corticosterone, plasma levels of glucose and triglycerides were not altered significantly. Circulating levels of cholesterol and free fatty acids increased significantly following both 14 and 28-day infusions of the hormone. Corticosterone treatment for 28 days produced significant increases in plasma levels of thyroxine (T4) and triiodothyronine (T3). However, following the 14-day corticosterone infusion, only T3 showed significant increase. The T3:T4 ratio in both groups of corticosterone-infused hens was significantly higher than in control hens. The concentration of plasma epinephrine showed no significant response to corticosterone treatment, while norepinephrine increased significantly following both periods of treatment.

Effects of vagotomy on circulating levels of catecholamines and corticosterone in the pigeon

The effects of bilateral cervical vagotomy on the blood levels of corticosterone, and catecholamines, adrenaline (A) and noradrenaline (NA), in pigeons, were studied. Plasma levels of corticosterone and NA were found to be significantly higher and of A lower, in the vagotomized (VgX) pigeons as compared to their sham-operated (VgS) controls. These changes in VgX pigeons are explained as caused mainly by the lack of the vagal tone.

The effects of ACTH and dexamethasone upon plasma thyroid hormone levels and heat production in the domestic fowl

Treatment with long acting ACTH (20 IU kg-1) produces a large and sustained elevation of plasma corticosterone in the domestic fowl. Both ACTH treatment and administration of dexamethasone produce significant reductions in plasma concentrations of T4 and T3, and these changes are accompanied by a sustained hyperglycaemia. Despite the changes in circulating thyroid hormones only a small reduction in heat production (-14%) was induced by either treatment and mainly during the dark period. Whilst there may be some causal relationship between increased corticosterone secretion, decreased plasma thyroid hormone levels and reduced metabolic heat production it is unlikely that these responses alone account for the adjustments in energy expenditure observed in short term food deprivation.