Mediation of glucagon in the response of the domestic fowl to stress

The Role of Glucagon in Regulating Chicken Hepatic Malic Enzyme and Histidase Messenger Ribonucleic Acid Expression In Response to an Increase in Dietary Protein Intake

Increased dietary protein intake rapidly (3 h) decreases hepatic malic enzyme and increases hepatic histidase mRNA expression in broiler chicks. A series of experiments was conducted to determine the role that glucagon or a specific mixture of dietary amino acids might have in regulating the rapid changes in mRNA expression of these enzymes, when dietary protein intake is increased. Three hours after the injection of glucagon (240 microg/kg of BW) into the brachial vein of broiler chicks, hepatic malic enzyme mRNA expression was significantly lower and hepatic histidase mRNA expression was significantly greater than the level detected in saline-injected chicks. In addition, broiler chicks fed a high (40 g/ 100 g of diet) protein diet had significantly higher plasma glucagon levels at 1 and 3 h after initial access to this diet than broiler chicks fed a basal (22 g/100 g of diet) protein diet. The plasma glucagon concentration, however, was not different between the chicks fed the 2 dietary protein levels at 2 h after the initial access to the 2 diets. When a mixture of indispensable or dispensable amino acids was added to the basal diet to equal the concentrations of the individual indispensable or dispensable amino acids in the high protein diet, hepatic mRNA expression of malic enzyme and histidase were intermediate to the expression found in chicks fed the basal and high protein diet. The results indicate that glucagon may mediate the changes in the mRNA expression of malic enzyme and histidase in response to dietary protein intake and that total amino acid intake rather than the ingestion of specific amino acids regulates the mRNA expression of malic enzyme and histidase in chicks.

Glucose regulates lipid metabolism in fasting king penguins

This study aims to determine whether glucose intervenes in the regulation of lipid metabolism in long-term fasting birds, using the king penguin as an animal model. Changes in the plasma concentration of various metabolites and hormones, and in lipolytic fluxes as determined by continuous infusion of [2-3H]glycerol and [1-14C]palmitate, were examined in vivo before, during, and after a 2-h glucose infusion under field conditions. All the birds were in the phase II fasting status (large fat stores, protein sparing) but differed by their metabolic and hormonal statuses, being either nonstressed (NSB; n = 5) or stressed (SB; n = 5). In both groups, glucose infusion at 5 mg.kg-1.min-1 induced a twofold increase in glycemia. In NSB, glucose had no effect on lipolysis (maintenance of plasma concentrations and rates of appearance of glycerol and nonesterified fatty acids) and no effect on the plasma concentrations of triacylglycerols (TAG), glucagon, insulin, or corticosterone. However, it limited fatty acid (FA) oxidation, as indicated by a 25% decrease in the plasma level of beta-hydroxybutyrate (beta-OHB). In SB, glucose infusion induced an approximately 2.5-fold decrease in lipolytic fluxes and a large decrease in FA oxidation, as reflected by a 64% decrease in the plasma concentration of beta-OHB. There were also a 35% decrease in plasma TAG, a 6.5- and 2.8-fold decrease in plasma glucagon and corticosterone, respectively, and a threefold increase in insulinemia. These data show that in fasting king penguins, glucose regulates lipid metabolism (inhibition of lipolysis and/or of FA oxidation) and affects hormonal status differently in stressed vs. nonstressed individuals. The results also suggest that in birds, as in humans, the availability of glucose, not of FA, is an important determinant of the substrate mix (glucose vs. FA) that is oxidized for energy production.

Stress and nutritional quality of broilers

Broiler chicks were reared in environmental chambers. All birds were started under ideal conditions, i.e., 30.6 C with 35% RH. Beginning at Day 36, half of the chicks were maintained at 24 C and 35% RH. The other half were subjected to a cyclic temperature-RH regime that approximated a typical August day in central Mississippi (heat treatment). Half of each of the described groups received implants of osmotic pumps that released adrenocorticotropin (ACTH) at 8 IU/kg BW/d for 7 d. The remaining birds received placebo pumps. The main effects of ACTH and heat treatments were similar. Both treatments caused reductions in BW, carcass weight (CW), carcass protein (CP), and muscle calorie (C) content. ACTH, but not heat, reduced carcass moisture (M). Carcass fat and ash, however, were not affected. Most changes were not reversed after 1 wk of recovery. Although visible signs of pale, soft, exudative muscle (PSE) were present, "white" areas of muscle were absent. The decreased meat yield and detrimental changes in meat quality suggest that stress, whether induced hormonally or by exposure to over-heating, caused losses that were as severe as those associated with PSE under field conditions.

Model of physiological stress in chickens 2. Dosimetry of adrenocorticotropin

Continuous adrenocorticotropin (ACTH) delivery by mini-osmotic pumps is a reliable method to induce stress in broilers. The present study was conducted to determine the minimum effective dose of ACTH that will evoke physiological stress. Chicks, which had been reared under floor-pen conditions until 5 wk of age received mini-osmotic pumps by surgical implantation. The mini-osmotic pumps delivered 2, 4, 8, or 16 IU of porcine ACTH/kg BW/d for 7 consecutive d. Controls (CON) were untreated chicks. Continuous infusion of ACTH caused dose-related stress responses. Chicks that received 8 or 16 IU showed the greatest responses, whereas those that received 2 or 4 IU were intermediate to the birds dosed with high ACTH and the CON birds. Responses included decreased BW; decreased relative weights of the bursa of Fabricius, thymus, and spleen; and increased relative liver weight. Concomitantly, increased liver lipid and decreased liver moisture were recorded. Plasma concentrations of corticosterone (CS), glucose (GLU), total protein (TP), cholesterol (CHOL), and triglycerides (TRI) and the ratio of heterophils to lymphocytes were increased during ACTH infusion. ACTH infusion at 8 IU/kg BW/d for 7 d was determined to be the minimum effective dose that caused physiological stress in broilers.

Metabolic responses of the turkey hen (Meleagris gallopavo) to an intravenous injection of chicken or porcine glucagon

The purpose of this study was to compare the metabolism of chicken and porcine glucagon in the turkey hen. Six hens each were infused with either porcine or chicken glucagon (16.6 micrograms/kg body weight). Blood samples were obtained at intervals pre- and post-infusion and analyzed for glucagon, glucose, insulin, free fatty acids, thyroxine (T4) and triiodothyronine (T3). The half-life (T 1/2) of porcine (4.5 min) and chicken glucagon (5.5 min) were similar. A 13% increase in glucose concentrations occurred within 10 min and remained elevated (22%) for 2 hr. A concomitant increase in insulin was noted, though not significant from pre-injection levels. A 50% increase in free fatty acids occurred in 2 min, reaching a zenith at 10-15 min post-treatment, and returned to baseline by 2 hr. Significant (P < 0.05) decreases in the circulating concentrations of both T3 and T4 hormones were observed within 5-10 min post-glucagon treatment and remained suppressed for the duration of sampling. These data indicate that the hormonal and metabolic responses of female turkeys to mammalian and avian glucagon are similar.

Effect of ACTH and glucocorticoids on lipid metabolism in the Japanese quail, Coturnix coturnix japonica

1. Immature male Japanese quail received repeated (chronic) injections of 0.8 I.U. corticotrophin (ACTH), 0.1 mg or 1.0 mg corticosterone (B), or 0.02 mg dexamethasone (DXM) and were fasted then refed at the end of the treatment period. A subgroup of the DXM group were given a single (acute) injection of 0.8 I.U. ACTH or saline before refeeding. A further group that had been given repeated injections of saline were fasted at the end of the treatment period. 2. All chronic hormone treatments decreased the rate of body weight gain and increased food consumption. Only the higher dose of B increased the lipid content of the carcass. This treatment and DXM also decreased the non-fat content of the carcass. 3. Plasma glucose and free fatty acids (FFA) were not altered by the chronic hormone treatments except DXM which increased plasma FFA. Acute injections of ACTH increased levels of plasma FFA and glucose in both controls and DXM-treated quails. Plasma glucose, but not FFA, was decreased by fasting. 4. De novo hepatic fatty acid synthesis in vitro was unaffected by the chronic treatments, whilst acute injections of ACTH or fasting decreased it.

Comparative effects of adrenaline and noradrenaline on the synthesis and secretion of soluble protein by isolated hepatocytes

1. Adrenaline (A) supplementation of the incubation medium of monolayer cultures of hepatocytes at 0.1, 0.2, 0.3, 1 and 10 ng/ml resulted in consistently enhanced levels of secreted and newly synthesised non-secreted proteins; supplementation with 100 and 1000 ng/ml resulted in lower or unchanged levels. These effects were most consistent 6 hr after a medium change. 2. Noradrenaline supplementation of the medium resulted in increased levels of secreted and non-secreted proteins at low concentrations (less than 2.4 ng/ml) at 6 hr after a medium change, but significantly decreased levels of both populations at high concentrations of noradrenaline (NA) (2.4 less than NA less than 1000 ng/ml), at 6-9 hr after a medium change and sustained to 24 hr, the most significant decrease being at 10 ng/ml. 3. All combinations of concentrations of A + NA resulted in non-dose-dependent decreased levels of both the secreted and non-secreted soluble protein fractions. The most significant decreases occurred at concentrations of (1 + 5) and (10 + 10) ng/ml adrenaline + noradrenaline. 4. Medium supplementation with adrenaline, noradrenaline or a combination of the two had no effect on the uptake of [3H]leucine by the cells. 5. The results are discussed in relation to receptor status on the hepatocyte membranes.

Effect of feed deprivation on hepatic membrane and lipoprotein fluidity and binding of lipoproteins to hepatic membranes in the chick (Gallus domesticus)

1. Male chicks were deprived of feed for 48 hr to study the effect of metabolic stress on hepatic membrane and lipoprotein fluidity and binding of radioiodinated lipoproteins to hepatic membranes. 2. Plasma levels of low density lipoprotein (LDL) and high density lipoprotein (HDL) were markedly and slightly elevated, respectively. 3. There was a reduction in lipoprotein and hepatic membrane fluidity. 4. Binding of [125I]LDL, but not [125I]HDL, to hepatic membranes was decreased. 5. It is suggested that a reduction in the fluidity of LDL and/or hepatic membranes impedes LDL catabolism in vivo.

Effect of fatty acid administration on plasma thyroid hormones in the domestic fowl

In birds a severe stress is associated with a reduction in concentrations of plasma thyroxine. Studies in man and the rat have demonstrated that severe illness is associated with an increase in serum concentrations of free fatty acids, notably oleic acid, and that they are associated with a reduction in concentrations of serum thyroxine (T4) and/or triiodothyronine (T3). Since stress is associated with increased fatty acids in birds, we have, in the present study, examined the role of oleic acid and another polyunsaturated fatty acid, arachidonic acid, on thyroid function tests (plasma thyroxine, triiodothyronine, and T3 resin uptake (RT3U) index) and on the thyroidal response to exogenous thyroid-stimulating hormone (TSH) in the domestic fowl. In the first study we observed that the iv administration of arachidonic (10 mg/kg) or oleic acid (15 mg/kg) to groups of 10-week-old cockerels (six per group) was associated with a significant reduction in concentrations of plasma T4, whereas there was little change in saline-injected controls. However, administration of fatty acids to chickens was not associated with a significant change in RT3U index or in the levels of plasma T3. In the second study, groups of animals (n = 6) were injected with bovine TSH (0.5 IU/kg, im) or saline 2.5 hr after the fatty acid injection and blood samples were obtained at -2.5 to 24 hr after the TSH injection. A similar progressive increase in serum T4 was observed for the three groups studied whereas there was little change in the concentrations of plasma T3.(ABSTRACT TRUNCATED AT 250 WORDS)

Interorgan metabolism of amino acids, glucose, lactate, glycerol and uric acid in the domestic fowl (Gallus domesticus)

Arterial--venous differences for metabolites across liver, kidney and hindquarters were measured in fed or starved, artificially ventilated chickens. The results indicate that the liver takes up amino acids under both conditions. Urate and glucose are released by the liver in both the fed and the starved state. Lactate and amino acids are extracted from blood by the kidneys, and this increases in the starved chicken. Urate is removed from the circulation by the kidney in the fed and starved state and excreted. In the fed bird there is no significant arteriovenous difference of glucose across the kidney, but in the starved state the kidney releases glucose into the circulation. The hindquarters take up glucose in the fed but not in the starved state. The branched-chain amino acids valine and leucine were taken up by the hindquarters in the fed, but not the starved, chicken. Glycerol is released by the hindquarter of fed and starved chickens. In the starved state, alanine and glutamine represent 57% of the amino acids released by the hindquarter. Lactate is released by the hindquarter of starved chickens and represents the major gluconeogenic carbon source released by the hindquarter and taken up by kidney and liver. Although the liver is the major gluconeogenic organ in the starved chicken, the kidney accounts for approx. 30% of the glucose produced.

A preliminary report on the effects of parasitism by the leeches Theromyzon cooperi and Placobdella garoui on the physiology of the redbilled teal Anas erythrorhyncha

The effects of parasitism by leeches Theromyzon cooperi and Placobdella garoui on the redbilled teal Anas erythrorhyncha were investigated. Leeches with initial body mass ranging from 5.2 to 28.4 mg were allowed to parasitize redbilled teal clamped in Perspex containers. Theromyzon cooperi increased its body mass after parasitism with a mean of 10.5-fold compared to 6.9-fold for P. garoui. Changes were also observed in values of various haematological and biochemical variables of the redbilled teal monitored during this investigation.

A surgical technique for serial blood sampling or continuous infusion of adult turkey hens

A technique for cannulating the jugular vein of turkey hens is described. The procedure is relatively easy to perform with no deleterious effects elicited by the procedure. Cannulae have remained patent for up to 1 month.

A simple method for measuring albumin-bound non-esterified fatty acid concentration in laying-hen plasma

Selective precipitation of triglyceride-rich (TGR) lipoproteins with dextran sulphate and magnesium chloride provides a simple and effective means of determining albumin-bound non-esterified fatty acids, (NEFA) in laying-hen plasma. Albumin-bound NEFA concentrations in the plasma of laying hens fed ad libitum are very low. Most of the NEFA are associated with TGR-lipoproteins, and their concentration is directly proportional (r = 0.82) to TGR-lipoprotein concentration. Subcutaneous injection of glucagon into laying hens produces an approximately 50% increase in total plasma NEFA concentration that persists for at least 2 hr. Most of this increase occurs in the TGR-lipoproteins, but albumin-bound NEFA concentrations increase at least 5-fold before rapidly returning to near control values. These results demonstrate the importance of measuring both albumin- and TGR-lipoprotein-bound NEFA in studies of plasma fatty acid metabolism in the laying hen.

Re-establishment of the stress response in Gallus domesticus after hatching

Cold caused a hypercorticosteronaemia and hypothermia in the 2-day-old chick. Heat did not affect plasma corticosterone concentrations, despite the birds becoming hyperthermic. The 2-day-old chick has a lower resting concentration of corticosterone than the 1-day-old. The minimum effective dose of corticotrophin in stimulating a hypercorticosteronaemia was 0.5 IU/kg in the former, 1.0 IU/kg in the latter. It is concluded that stress non-responsiveness persists for about 48 hr after hatching and that it is due to a temporary inhibition of hypothalamic function.

Hyperinsulinemia and its role in maintaining the hypothalamic hyperphagia in chickens

Electrolytic lesions of the ventromedial hypothalamus including nucl. hypothalamicus inferior caused the cockerels to become hyperphagic. The plasma insulin level of the control birds was low before feeding and it increased after feeding, while that of the hyperphagic birds was higher before feeding and increased even more after feeding. Under the fasting condition on the 19th day, the insulin secretion of the hyperphagic birds remained at a high level, and there was a high correlation between the insulin value and the food consumption. Hyperactivity of insulin secretion in the hypothalamic hyperphagic birds was inhibited by administration of diazoxide and their insulin levels declined to a level similar to that of the controls. As a result the hyperphagia was interrupted and the daily food consumption declined to the same level as the controls. Therefore, the hyperinsulinemia seemed to be necessary for maintaining the hypothalamic hyperphagia in chickens. The role of glucagon in this phenomenon is also discussed.

Dietary ascorbic acid or procaine penicillin and the response of the immature fowl to stressors

1. The effectiveness of dietary ascorbic acid and procaine penicillin in ameliorating the response to the stressors glucagon, corticotrophin, withdrawal of food and water and extremes of environmental temperature, both short and long-term, has been assessed. 2. No consistent changes in the responses were found, but it is suggested that the rates of inclusion of the substances may be important.

The effects of restricted feeding on adrenal cortical activity in the immature domestic fowl

1. The effect of reducing food intake to 75% of the ad libitum intake was determined from hatching to 8 weeks in young Light Sussex chickens. 2. Restricted birds were lighter throughout the experiment. 3. Relative adrenal weight tended to be greater in restricted birds but the difference decreased with time. 4. There was no depletion of adrenal cholesterol: from week 5 there was a significantly greater amount in the adrenals of restricted birds. 5. After 1 week of restriction plasma corticosterone concentration was 73% greater than in controls. It decreased progressively, falling within the normal range at 5 weeks. 6. Restricted birds were hypoglycaemic from weeks 2 to 7 and hyperlipacidaemic throughout. A negative correlation between plasma glucose and free fatty acids was found.

Short-term stressor effects of propranolol

1. The effects of propranolol (10 mg/kg) on plasma cholesterol, glucose, corticosterone and free fatty acids, on adrenal mass and cholesterol content and on body temperature were determined over a 24-h period in 3-week-old Light Sussex chicks. 2. Changes in plasma cholesterol were equivocal, though there was perhaps a trend towards hypercholesteraemia. 3. Birds became hypoglycaemic within an hour but were hyperglycaemic between 2 and 4 h. At 24 h they were normoglycaemic. 4. Plasma corticosterone was increased markedly at 1 h but was decreased compared with the control at 2 h ( P < 0.01). Thereafter the concentration was in the normal range. 5. There was an enhanced hyperlipacidaemia in the treated birds after 1 h. 6. Adrenal cholesterol stores were decreased by 10% at 4 h but were unaffected at all other times. 7. Colonic temperature decreased by 1x6 degrees C after 2 h but was normal by 4 h. 8. It is concluded that propranolol has mild stressor activity which is lost within 24 h.

Short-term stressor effects of reserpine

The effects of reserpine on plasma glucose, FFA and cholesterol and on adrenal cholesterol were determined in 1-and 21-d-old chicks over a 24-h period. 2. Irrespective of age, reserpinised chicks became hyperglycaemic and hypocholesteraemic, their stores of adrenal cholesterol were depleted and the mobilisation of the lipid was impaired. The response of the older bird was quantitatively larger than that of the younger bird. 3. Propranolol prevented the increase in plasma glucose concentration seen 1 h after reserpine but it did not affect subsequent changes. 4. It is concluded that reserpine acts as a stressor and it is shown that its effects have not been entirely overcome after 24 h.