Effect of environmental temperatures on the catecholamines of chickens

Avian adjustments to cold and non-shivering thermogenesis: whats, wheres and hows

Avian cold adaptation is hallmarked by innovative strategies of both heat conservation and thermogenesis. While minimizing heat loss can reduce the thermogenic demands of body temperature maintenance, it cannot eliminate the requirement for thermogenesis. Shivering and non-shivering thermogenesis (NST) are the two synergistic mechanisms contributing to endothermy. Birds are of particular interest in studies of NST as they lack brown adipose tissue (BAT), the major organ of NST in mammals. Critical analysis of the existing literature on avian strategies of cold adaptation suggests that skeletal muscle is the principal site of NST. Despite recent progress, isolating the mechanisms involved in avian muscle NST has been difficult as shivering and NST co-exist with its primary locomotory function. Herein, we re-evaluate various proposed molecular bases of avian skeletal muscle NST. Experimental evidence suggests that sarco(endo)plasmic reticulum Ca²⁺ -ATPase (SERCA) and ryanodine receptor 1 (RyR1) are key in avian muscle NST, through their mediation of futile Ca²⁺ cycling and thermogenesis. More recent studies have shown that SERCA regulation by sarcolipin (SLN) facilitates muscle NST in mammals; however, its role in birds is unclear. Ca²⁺ signalling in the muscle seems to be common to contraction, shivering and NST, but elucidating its roles will require more precise measurement of local Ca²⁺ levels inside avian myofibres. The endocrine control of avian muscle NST is still poorly defined. A better understanding of the mechanistic details of avian muscle NST will provide insights into the roles of these processes in regulatory thermogenesis, which could further inform our understanding of the evolution of endothermy among vertebrates.

Pulmonary arterial hypertension (ascites syndrome) in broilers: a review

Pulmonary arterial hypertension (PAH) syndrome in broilers (also known as ascites syndrome and pulmonary hypertension syndrome) can be attributed to imbalances between cardiac output and the anatomical capacity of the pulmonary vasculature to accommodate ever-increasing rates of blood flow, as well as to an inappropriately elevated tone (degree of constriction) maintained by the pulmonary arterioles. Comparisons of PAH-susceptible and PAH-resistant broilers do not consistently reveal differences in cardiac output, but PAH-susceptible broilers consistently have higher pulmonary arterial pressures and pulmonary vascular resistances compared with PAH-resistant broilers. Efforts clarify the causes of excessive pulmonary vascular resistance have focused on evaluating the roles of chemical mediators of vasoconstriction and vasodilation, as well as on pathological (structural) changes occurring within the pulmonary arterioles (e.g., vascular remodeling and pathology) during the pathogenesis of PAH. The objectives of this review are to (1) summarize the pathophysiological progression initiated by the onset of pulmonary hypertension and culminating in terminal ascites; (2) review recent information regarding the factors contributing to excessively elevated resistance to blood flow through the lungs; (3) assess the role of the immune system during the pathogenesis of PAH; and (4) present new insights into the genetic basis of PAH. The cumulative evidence attributes the elevated pulmonary vascular resistance in PAH-susceptible broilers to an anatomically inadequate pulmonary vascular capacity, to excessive vascular tone reflecting the dominance of pulmonary vasoconstrictors over vasodilators, and to vascular pathology elicited by excessive hemodynamic stress. Emerging evidence also demonstrates that the pathogenesis of PAH includes characteristics of an inflammatory/autoimmune disease involving multifactorial genetic, environmental, and immune system components. Pulmonary arterial hypertension susceptibility appears to be multigenic and may be manifested in aberrant stress sensitivity, function, and regulation of pulmonary vascular tissue components, as well as aberrant activities of innate and adaptive immune system components. Major genetic influences and high heritabilities for PAH susceptibility have been demonstrated by numerous investigators. Selection pressures rigorously focused to challenge the pulmonary vascular capacity readily expose the genetic basis for spontaneous PAH in broilers. Chromosomal mapping continues to identify regions associated with ascites susceptibility, and candidate genes have been identified. Ongoing immunological and genomic investigations are likely to continue generating important new knowledge regarding the fundamental biological bases for the PAH/ascites syndrome.

Behavioral responses of neonatal chicks exposed to low environmental temperature

Research has shown that on exposure to low environmental temperature, neonatal chicks (Gallus gallus) show hypothermia and absence of gene transcript enhancement of putative thermogenic proteins, mitochondrial fatty acid transport, and oxidation enzymes. Various behavioral abnormalities may also decrease the thermogenic capacity of low-temperature-exposed neonatal chicks. Therefore, to investigate behavioral irregularities in low-temperature-exposed (20 degrees C) neonatal chicks, we studied behavioral responses when compared with the control kept at thermoneutral temperature (30 degrees C). Two-day-old chicks (n = 5) were exposed to either low or thermoneutral temperature for 3 h and were then immediately placed in an acrylic monitoring cage (40 x 30 x 20 cm). The monitoring cage was fitted with a 3-dimensional mirror (to prevent isolation-induced stress) and maintained either at 20 or 30 degrees C. Behavioral responses were monitored for 10 min. Behavioral observations revealed that low-temperature exposure decreased distress vocalizations and spontaneous activity. Low-temperature exposure induced sleep-like behavior in neonatal chicks; active wakefulness was decreased while standing or sitting motionless with eyes closed or open and sleeping posture was significantly increased. In conclusion, there is evidence that on exposure to low-temperature, neonatal chicks decrease behavioral activity. Increased sleep-like behavior and decreased activity may reduce heat production in low-temperature-exposed neonatal chicks and could potentiate the sensitivity to cold exposure.

Influence of long-term changes in incubation temperature on catecholamine levels in plasma of chicken embryos (Gallus gallus f. domestica)

Catecholamine concentrations were determined from day 18 to 21 of incubation (D18, D21) in developing chicken embryos. The control group was continuously incubated at 37.5 degrees C. The eggs of the two other groups were incubated at 37.5 degrees C until day 14. In the cold group, temperature was decreased to 35.0 degrees C and in the warm group, incubation temperature was increased to 38.5 degrees C for the remainder of incubation. Plasma catecholamine concentrations were measured in eggs exposed to a change in incubation temperature for 4, 5, 6 and 7 days. Embryos in the warm group had dopamine (DA) and noradrenaline (NA) concentrations that were significantly higher than in the control group. On the contrary, eggs incubated at the cooler temperature had hormone levels that were significantly lower than in the control group. Adrenaline (A) levels in the two experimental treatments were significantly lower compared to control eggs. Temperature modulated the time needed for development. Chicken embryos are supposed to hatch on day 21. However, on day 20, NA concentration in the cold-incubated group was too low to fulfill its essential physiological function, whereas in the warm group, the NA concentration seems to be sufficient. Long-term exposure to altered incubation temperature affects the quantitative catecholamine concentration during development, but the relative proportion of each catecholamine remained constant.

Cardiac output in four-, five-, and six-week-old broilers, and hemodynamic responses to intravenous injections of epinephrine

Female broilers were evaluated at 4, 5, and 6 wk of age (1.2, 1.8, and 2.3 kg BW, respectively) to assess changes in cardiac output and related hemodynamics associated with BW gain, and to evaluate cardiopulmonary hemodynamic adjustments occurring secondary to i.v. injections of epinephrine (0.1 mg/ kg BW). Cardiac output increased with BW (253, 348, and 434 mL/min at 4, 5, and 6 wk, respectively) due to increases in stroke volume (0.70, 1.03, and 1.33 mL/beat) that more than compensated for reductions in heart rate (362, 337, and 328 bpm). Normalization for BW eliminated the differences in cardiac output and stroke volume. Increases in cardiac output were not associated with age- or BW-related increases in mean systemic arterial pressure (101.5, 108.6, and 108.0 mm Hg) due to corresponding reductions in total peripheral resistance (0.41, 0.32, and 0.26 relative resistance units). Epinephrine initially triggered immediate (within 90 s) threefold increases in total peripheral resistance and pulmonary vascular resistance, which, in turn, increased the systemic arterial pressure and pulmonary arterial pressure in spite of concurrent reductions in cardiac output that were associated with diminished venous return and dependent reductions in stroke volume and heart rate. Within 150 s after epinephrine injection, the systemic and pulmonary vascular resistances returned to preinjection control levels. By 300 s postinjection, stroke volume and heart rate increased, causing cardiac output to rise above preinjection control levels, which, in turn, elicited variable pulmonary arterial pressure responses apparently reflecting individual variability in the capacity for flow-dependent pulmonary vasodilation. These studies demonstrate that chronic (age- and BW-related) and acute (epinephrine-induced) changes in cardiac output in broilers reflect complex interactions among hemodynamic variables that include stroke volume, heart rate, and systemic and pulmonary vascular resistances.

Localization and changes in distribution of brain alpha 2- and beta-adrenoceptors in response to acclimation state in the American bullfrog (Rana catesbeiana)

Alpha (alpha)- and beta (beta)-adrenoceptors regulate physiological processes in vertebrates. This study determined the location of alpha 2- and beta-adrenoceptors in the brain of the American bullfrog, Rana catesbeiana, using autoradiography. As the density of receptors may be affected by environmental temperature, a comparative numerical analysis of adrenoceptors in the areas of localization with respect to warm and cold acclimation was also carried out. Areas of greatest concentration of alpha 2-adrenoceptors were the accessory olfactory bulb, medial pallium, and olfactory bulb. Adrenoceptor numbers were significantly decreased in the accessory olfactory bulb and medial pallium in cold-acclimated animals. beta-adrenoceptors were localized in the thalamus, cerebellum, medial pallium, and amygdala/ striatum. Cold acclimation decreased adrenoceptor density in medial pallium and torus semicircularis and increased adrenoceptor density in the thalamus and hypothalamic preoptic areas. Among the alpha 2- and beta-adrenoceptors, only four regions of overlap existed, the medial pallium, hypothalamic preoptic area, optic tract, and isthmic tegmentum. Otherwise, where there were alpha 2-adrenoceptors, there were few or no beta-adrenoceptors. No alpha 2- or beta-adrenoceptors were found in the pituitary and optic chiasm. The distribution of adrenoceptors in particular areas of the brain may have functional significance with respect to physiological changes which occur in response to hibernation.

Potential for non-shivering thermogenesis in perfused chicken (Gallus domesticus) muscle

The humoral modulation of resting muscle heat production of chickens (Gallus domesticus) was investigated in vitro. The resting distal lower limb was perfused via the popliteal artery at 25 degrees C without erythrocytes at constant flow. The preparation was stable for at least 3 hr, showing a constant oxygen uptake (MO2) and perfusion pressure as well as adequately maintaining muscle energy charge and creatine phosphate: creatine ratio. Noradrenaline (NOR), adrenaline (ADR) and serotonin (5-HT) each caused a dose-dependent rise in perfusion pressure. NOR and ADR evoked increased MO2 at low doses eventually followed by decreased MO2 at higher agonist concentrations. 5-HT gave smaller but qualitatively similar MO2 effects. The actions of 50 nM NOR were blocked by prazosin (10 microM) and nitroprusside (0.5 mM), but not altered by propranolol (10 microM). NOR-induced stimulatory MO2 changes in the presence of pharmacological concentrations (1 microM) of glucagon were more pronounced and the thermogenic concentration range of NOR was increased. Taken together, these in vitro findings demonstrate a potential for vasoconstrictor-controlled muscle nonshivering thermogenesis in birds as in marsupials and mammals, suggesting that vascular control of muscle MO2 may be a widespread biological mechanism. The possible implications of these findings for avian nonshivering thermogenesis are discussed.

Effect of chemical sympathectomy on serum levels of thyroid hormones and the biochemical profile of domestic pigeons

Recent studies have stressed the importance of the cholinergic system on avian metabolism. However, the role of the sympathetic nervous system (SNS) remains unclear. The present study was, therefore, aimed to probe the mechanisms for modulation of avian metabolism by the sympathetic nervous system after inhibition of the adrenergic responses. Activities of serum thyroid hormones (tri-iodothyronine, T3, and thyroxine, T4), body weight, hepatic weight, as well as total lipid and water content in the liver and body temperature were some of the parameters examined after chemical sympathectomy with 6-hydroxydopamine (6-OHDA) and reserpine treatment in 24-h starved pigeons. In addition, glucose was administered to the pigeons to identify the regulatory role played by glucose after disruption of the SNS. A reduction in body weight of the pigeons and an enhancement in the lipogenic machinery along with a corresponding increase in water content were some of the obvious effects in 6-OHDA+reserpine treated, as well as glucose-loaded sympathectomized birds. The cloacal temperature (Tc) and both the thyroid hormones showed a drastic decrease while the T3/T4 ratio was augmented as a result of sympathectomy. However, serum T3 and T4 levels were restored to control values when glucose load was given, indicating that glucose might be reversing some of the detrimental effects of 6-OHDA treatment by activating intrinsic autoregulatory mechanisms of thyroid gland, thereby reviving the levels of thyroid hormones. Thus, the influence of SNS appears to be crucial in the maintenance of serum thyroid hormones and body temperature, as well as metabolic activities of hepatic cells.

Effect of stress on the catecholamine content of the adrenal gland of intact and bursectomized chicks

1. Bursa-intact and bursectomized chicks were exposed to cold-wet immobilization (CWI) stress for 1.5 min. The catecholamines (CA) from the adrenal gland were measured spectrofluorometrically 5, 15, 30 and 60 min after stress. 2. In bursa-intact chicks, the CWI stress caused decrease of both norepinephrine and epinephrine from the adrenal glands 5 min after stress. Resynthesis of epinephrine exceeded the control value 30 and 60 min after stress. 3. In bursectomized chicks, the CWI stress brought about a decrease of norepinephrine 15 and 30 min and of epinephrine 30 and 60 min after stress. 4. The findings suggest that bursa facilitates early (5 min) release of CA and also helps in quick resynthesis of epinephrine during stress.

Blood plasma catecholamine concentration of poult embryos during the transition from diffusive to convective respiration

1. Plasma catecholamines were determined in turkey embryos. 2. Decreased eggshell permeability depressed dopamine and epinephrine, but increased permeability also depressed epinephrine. 3. Norepinephrine (NE) was greatest before transition to convective respiration when hypoxia occurs. 4. NE was associated inversely with eggshell permeability. 5. Catecholamines appear to assist the embryo during hatching hypoxia.

Alpha adrenergic regulation of celiac blood flow and plasma catecholamine response during acute heat stress in fed cockerels

Hubbard cockerels with chronically implanted electromagnetic blood flow probes on the celiac artery were used to establish a relationship between changes in postprandial celiac mean blood flow (MBF) and plasma catecholamines during a acute heat exposure. Five min after the elevation of ambient temperature from 25 to 37 C, there were concomitant reductions (P less than .05) in celiac MBF, norepinephrine (NE), and heart rate (HR). After 50 min of heat stress, rectal temperature (Tr), respiratory rate (RR), plasma epinephrine (E), and celiac vascular resistance (CVR) were significantly greater (P less than .05) than preheat stress thermoneutral control values. During the thermoneutral recovery period, all parameters returned to values comparable to preheat exposure control with the exception of NE, which tended (P less than .1) to remain lower. To determine the role of the sympathetic nervous system in regulating postprandial celiac MBF during acute heat exposure, chronically instrumented cockerels were infused with phenoxybenzamine, an alpha-adrenergic receptor-blocking agent. Alpha-receptor blockade attenuated both postprandial intestinal hyperemia under thermoneutral conditions as well as the heat-induced reduction of postprandial celiac MBF. The results of these studies implicate the sympathetic nervous system in the regulation of postprandial celiac MBF in heat-stressed cockerels and indicate a possible alpha-adrenergic-mediated mechanism involved in postprandial intestinal hyperemia.

Stress and adrenal function

The natural environment is composed of various potentially hostile stressors. It is a basic requirement of life that the cells of an organism must be maintained within closely defined physiological limits. The maintenance of a constant interior mileu results from physiological and behavioural homeostatic adaptations. The physiological regulation of homeostatis is achieved by complex endocrine interactions, principally by the hormones secreted from the adrenal glands. In this brief review the responses of the avian adrenal glands to stressful stimuli, the mechanism of adrenal activation, and the function of the adrenal responses will be considered.

Adrenergic regulation of insulin secretion from the chicken pancreas in vitro

Adrenergic regulation of insulin secretion in the chicken was studied using a perifused pancreas fragment preparation. Beta-adrenergic stimulation by 50 microM isoproterenol potentiated theophylline-stimulated insulin secretion. Glucose at 19.5 mM did not stimulate insulin secretion, a finding consistent with previous reports of chicken pancreas sensitivity in vitro. Pretreatment with 50 microM isoproterenol did not alter this glucose insensitivity. Alpha-adrenergic stimulation by 50 microM epinephrine in the presence of beta blockade by sotalol or by 50 microM phenylephrine did not alter insulin secretion. Inhibition of insulin secretion by somatostatin could be demonstrated, however. Epinephrine, 50 and 0.164 microM, potentiated theophylline-stimulated insulin release and at 50 microM stimulated insulin secretion as an off-response even in the absence of theophylline. It is concluded that adrenergic regulation of insulin secretion in the chicken is primarily mediated through beta-adrenergic receptors, resulting in stimulation of insulin secretion.

The effects of ambient temperature on urinary flow and composition in the fowl

1. Urine flow and compositions were determined in normally hydrated, waterloaded and hypotonic saline infused hens under various ambient temperatures (Ta). 2. At Ta 29 and 32 degrees C normal urine flow was reduced and osmolality increased; at Ta 0 and -5 degrees C urine flow increased and osmolality decreased. 3. In hydrated hens at Ta 32 degrees C antidiuresis occurred within 10 min and persisted for 2 hr without any significant change in rectal temperature (Tr). 4. At Ta 40 degrees C there was no antidiuresis but a tendency for urine flow to increase; Tr also rose. The antidiuresis shown by water-restricted hens at Ta 20 degrees C was abolished at Ta 40 degrees C. 5. An antidiuresis, similar to that seen at Ta 32 degrees C, could be produced at Ta 20 degrees C by moderate haemorrhage, exposure to infra-red heating or by vasopressin or vasotocin. Adrenaline and noradrenaline provoked a diuresis. 6. Hypothalamic heating failed to elicit an antidiuresis but hypothalamic cooling increased urine flow at Ta 20 degrees C and abolished the antidiuretic response at Ta 32 degrees C. 7. It is concluded that the antidiuresis seen at warm ambient temperatures is caused by the release of antidiuretic hormone possibly as a response to a rise in skin temperature.

Effect of restraint upon hypothalamic and adrenal catecholamines in Japanese quail

1. Changes in catecholamine concentration after periods of restraint up to 48 h in male Japanese quail have been measured. 2. Hypothalamic catecholamines decreased after 10 min restraint. Dopamine concentration increased after 4 h and persisted to 48 h. 3. Plasma catecholamines increased after 10 min, remained high for 2 h and then decreased despite continuing restraint. Catecholamine content of adrenals slightly decreased during restraint. 4. The activity of adrenal phenylethanolamine-N-methyl transferase increased from the 4th hour of restraint.

Evidence for noradrenaline and adrenaline as sympathetic transmitters in the chicken

1 The concentrations of noradrenaline and adrenaline in various organs, arterial plasma and venous outflow from isolated hearts of adult chickens have been determined. 2 The relative adrenaline concentrations (percentage of the sum of noradrenaline and adrenaline) in the heart (33%), spleen (16%) and brain (26%) were higher than those found in mammalian organs. Chemical sympathectomy by pretreatment with 6-hydroxydopamine caused a decrease of the noradrenaline and adrenaline concentrations in the heart to 20 and 23% and in the spleen to 16 and 29%, respectively. 3 Stimulation of the right sympathetic nerves, infusion of tyramine or infusion of a modified Tyrode solution containing 108mM K+ and 44 mM Na+ caused an output of both noradrenaline and adrenaline into the perfusate of isolated hearts. The relative adrenaline concentration in the perfusate (20-28%) was not significantly different from the relative adrenaline concentration remaining in these hearts (19-22%). In the individual experiments, the noradrenaline: adrenaline ratios of the stimulation perfusates were positively correlated with the ratios found in the hearts. 4 The effects of noradrenaline and adrenaline on cardiac rate and tension development were studied in spontaneously beating right atria and electrically driven left atria, respectively. In addition, the arterial pressure rise in response to noradrenaline or adrenaline was;measured in chickens. It was found that the cardio-vaseart rate, cardiac tension development and arterial blood pressure, was not significantly different from that of adrenaline. 5 It is concluded that, in the chicken heart and spleen, both noradrenaline and adrenaline act as sympathetic neutrotransmitters.