The effects of corticosterone and catecholamine infusion on plasma glucose levels in chicken (Gallus domesticus) and Turkey (Meleagris gallapavo)

Camp. Biochem. Physiol.

Vol. 106C.

No. 1, pp. 5942,

0742-8413/93$6.00+ 0.00 0 1993Pergamon Press Ltd

1993

Printed in Great Britain

THE EFFECTS OF CORTICOSTERONE AND CATECHOLAMINE INFUSION ON PLASMA GLUCOSE LEVELS IN CHICKEN (GALLUS DOkfEsTICUS) AND TURKEY (MELEAGRIS GALLAPA VO)* R. J. THURSTON,~ C. C. BRYANT and N. KORN Department of Poultry Science, Clemson University, Poole Agricultural Center, Box 340379, Clemson, SC 29634-0378, U.S.A. (Tel. 803-656-3162; Fax 803-656-1033) (Received 16 March 1993; acceptedfor publication7 May 1993) Abstract-l. Continuous 5 hr infusion of low levels of corticosterone, epinephrine, isoproterenol or phenylephrine plus a high dose bolus injection at 3 hr had different effects on the plasma glucose levels of chickens and turkeys. 2. Corticosterone had no effect on plasma glucose in turkeys, but increased glucose after the bolus and at 270 and 300min for chickens. 3. Epinephrine increased plasma glucose in turkeys, but only caused a transient elevation after the bolus in chickens. 4. Isoproterenol increased plasma glucose in turkeys, but had no effect in chickens. 5. Phenylephrine increased plasma glucose after the bolus in turkeys but had no effect in chickens.

norepinephrine had little effect on plasma glucose levels in the turkey.

INTRODUCTION The avian adrenal gland plays a central role in mediation of stress. Plasma concentrations of corticosterone, the principle glucocorticoid in birds, as well as the catecholamines epinephrine and norepinephrine, have been shown to increase in both chickens and turkeys in response to stressors such as infection, temperature extremes, handling and blood sampling (Brown and Nester, 1973; El Halawani et al., 1973; Saleh and Jaksch, 1977; Beuving and Vonder, 1978; Lagadic et al., 1990; Augustine and Denbow, 1991). Increased levels of plasma glucose have also been observed in response to applied stressors (Saleh and Jaksch, 1977; Lagadic et al., 1990; Augustine and Denbow, 1991; Donaldson et al., 1991). Studies of the effects of the adrenal hormones on plasma glucose levels in chickens and turkeys have usually involved single injections of these substances at doses much higher than physiological levels. The current research was undertaken to investigate changes in chicken and turkey plasma glucose levels resulting from continuous infusion of approximate physiological doses of corticosterone and epinephrine, as well as the synthetic catecholamines isoproterenol (B-agonist) and phenylephrine, (a-agonist). Bolus injections of 3-20 times the infusion doses were also given midway through the infusion period. Norepinephrine was not tested as Grande (1969) has shown that administration of

MATERIALS AND METHODE Animals and reagents

Male chickens (Callus domesticus) and turkeys (Meleagris gallapauo) from commercial strains were used in these experiments. Birds were reared in littered-floor pens with 23 hr of light per day and had free access to food and water. Diets at the time the experiments were performed contained 18.93% protein and 3260 kcal/kg for chickens or 18.6% protein and 3210 kcal/kg for turkeys. Chickens were 7-9 weeks old and weighed 2.38-2.78 kg. Turkeys were 17-21 weeks old and weighed 7.8s13.26 kg. Corticosterone, L-epinephrine. HCl, DL-iSOproterenol . HCl and L-phenylephrine . HCI were purchased from Sigma Chemical Co. (St Louis, MO). Experimental procedures and glucose assay

To minimize the amount of activity around the birds during the experiment, only one bird and one treatment (corticosterone, epinephrine, isoproterenol, phenylephrine, or 0.9% NaCl) were tested at a time. This continued until five chickens and five turkeys had been tested with each treatment. The 5 hr treatment administration generally took place between 4:00 and 9:00 pm. About midday (and 4 hr prior to the start of treatment), a bird was transferred from its pen to an open-sided cage in the laboratory where it remained until completion of the experiment. The cage measured 12 x 16 x 18 in. for chickens and 24 x 30 x 36 in. for turkeys. Food was withheld from

*Technical Contribution No. 3360 of the South Carolina Agricultural Experimental Station. tTo whom correspondence should be addressed. 59

60

R. J. THURSTONei al. Table I. Treatment schedule and dose levels

Treatment

Time (min)

Injection rate

0.9% N&I

tS300 180 O-300 180 O-300 180 O-300 180 o-300 180

50.0 pl/min I.Oml 0.063 fig/kg/n& 1.27rg/kg f I.Oml) 2.5 pg/kg/min 50.0 fig/kg (I .Oml) 7.1 pg/kg/min 23.6rg/kg (1.01111) 5.0 Fg/kg/min 96.0 &kg (1 .Oml)

Corticosterone Epinephrine Isoproterenol Phenylephrine

this time until completion of the experiment, but free access to water was maintained throughout the study. Birds were not anesthetized during any phase of the experiment. Two hours prior to the start of infusion, heparinized indwelling cannulas were placed into both brachial veins. The cannula from the left vein was attached to a 50 cm3 syringe via a three-way stopcock. The syringe was placed in a Harvard Infusion Pump (South Natick, MA) for treatment administration. The cannula from the right vein was used for withdrawal of blood samples (0.5 ml). A blood sample was taken to determine the initial (&) plasma glucose concentration for each bird. One of the treatments (corticosterone, epinephrine, isoproterenol, phenylephrine, or 0.9% NaCl) was then continuously infused for 5 hr with a large bolus injection given at 180 min after the start of the infusion. The infusion and bofus dose level for each treatment are shown in Table 1. The NaCl was administered to determine the effects on glucose levels of 0.9% NaCl infusion superimposed on handling, confinement and general environmental stress. Blood samples were taken at 5, 15 and 30 min after beginning the infusion and at 30 min intervals thereafter to the end of the 5 hr period. In addition, a blood sample was taken at 5 and 15 min after the bolus injection, which was given immediately following the blood sample taken at 180min. Blood samples were centrifuged to remove the blood cells. The plasma was frozen at -20°C until assayed for glucose content using the hexokinase/glucose-6-phosphate dehydrogenase method (Glucose 15-UV Diagnostic Kit, Sigma Chemical Company, St Louis, MO). Glucose solutions (50-500 mg/lOOml) were used as standards. Absorbance at 340 nm was monitored using a Gilford Mode1 250 spectrophotometer (Oberlin, OH). Statistics

the corresponding presentation.

pretreatment

levels for graphic

RESULTS

The plasma glucose levels in the chickens during continuous infusion and bolus injection of corticosterone, epinephrine, isoproterenol, phenylephrine and 0.9% NaCl are shown in Fig. 1, There were no significant changes in glucose levels of chickens that received 0.9% NaCl during the 5 hr interval of the study. When corticosterone was administered to chickens, glucose levels were not significantly different from those prior to treatment (To) except at the 180 min, 270 min and 300 min intervals when levels were significantly elevated. The bolus injection of 20 times the infusion level, which occurred immediately after the 180 min blood sample, was followed by a return of plasma glucose to pre-treatment levels which did not become elevated again until the 270min and 300min samples. Administration of epinephrine to chickens resulted in no signi~~ant change in glucose levels, except for a transient significant 40% increase in plasma glucose levels immediately following the bolus injection, which decreased by 30 min post bolus. There was no significant change

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The mean plasma glucose concentration (mg/lOO ml) at each time period within a treatment group was determined, and statistical differences from the pretreatment concentrations were estimated by analysis of variance using the general linear models (GLM) of SAS (SAS Institute Inc., Cary, NC) with P < 0.05 considered significant. The glucose levels during treatment were also expressed as a percentage of

Fig. 1. Plasma glucose levels in chickens during continuous infusion of 0.9% NaCl, corticosterone, epinephrine, isoproterenol or phenylephrine for 5 hr. A bolus injection of 3-20 times the infusion dose was given immediately after the blood sample taken at 180min (arrow). Values are expressed as percentage of pretreatment glucose levels (T,) and are marked with an asterisk if significantly different from the T, value.

61

Plasma glucose levels in poultry in plasma glucose levels of chickens during administration of either isoproterenol or phenylephrine. The plasma glucose levels in turkeys during continuous infusion and bolus injection of corticosterone, epinephrine, isoproterenol, phenylephrine and 0.9% NaCl are shown in Fig. 2. There were no significant changes seen in the plasma glucose levels of turkeys that received either 0.9% NaCl or corticosterone during the 5 hr interval of the study. In contrast, administration of epinephrine resulted in a progressive increase in plasma glucose levels which approached significance by 60 min (P = 0.06) and remained significantly elevated throughout the rest of the study period. There was a spike increase following the bolus injection which lasted for 15 min before glucose levels returned to the pre-bolus elevated levels. The maximum increase in plasma glucose levels represented an 83% increase over that seen prior to treatment. Isoproterenol increased plasma glucose levels throughout the 5 hr continuous infusion, an effect which was significant by the 30 min interval. Glucose levels as high as 130% of the pretreatment levels were seen, and no additional effects due to the bolus were detected. Following phenylephrine administration to turkeys, there was no significant change in plasma glucose levels except during the 15 min interval immediately following the bolus injection.

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Fig. 2. Plasma glucose levels in turkeys during continuous infusion of 0.9% NaCl, corticosterone, epinephrine, isoproterenol or phenylephrine for 5 hr. A bolusinjection of 3-20 times the infusion dose was given immediately after the blood sample taken at 180 min (arrow). Values are expressed as percentage of pretreatment glucose levels (T,) and are marked with an asterisk if significantly different from the T, value.

DISCUSSION

The average plasma glucose levels in both the chickens and turkeys prior to treatment (234.1 + 8.5 mg/lOO ml and 224.3 f 10.2 mg/lOO ml, respectively) were within the normal range of previously reported values (Grande, 1968; Langslow et al., 1970; Freeman and Manning, 1974; Hazelwood and Cieslak, 1989; Lagadic et al., 1990; Augustine and Denbow, 1991; Donaldson er al., 1991). Glucose levels during administration of 0.9% NaCl in both chickens and turkeys were not significantly different from levels prior to treatment, so it is concluded that plasma glucose was not altered by the experimental procedures used in this study. The glucose elevations that occurred during corticosterone administration to chickens did not relate well with infused levels, and therefore may not have been a direct result of corticosterone. Corticosterone administration also had no significant effect on plasma glucose in the turkey. This is consistent with the idea that corticosterone causes modest hyperglycemia via gluconeogenesis, rather than by glycogenolysis as is the case for the catecholamines (Hazelwood, 1986). This would require a latent period because steroids act through DNA to stimulate the synthesis of proteins which usually orchestrate the steroid response. Thus, increases in plasma glucose levels resulting from corticosterone administration may be delayed and not detectable in the 5 hr time interval of this study. Catecholamines produce their effects through u - or /I-receptors. It is generally agreed that glycogenolysis in isolated hepatocytes, embryos, immature or adult chickens is stimulated by /?-agonists (Langslow et al., 1970; Freeman and Manning, 1974; Dickson et al., 1978; Picardo and Dickson, 1982). For the chickens in the present study, approximate physiological doses of epinephrine, a compound with both G(- and /Iactivity, did not significantly change plasma glucose levels and produced only a slight transient increase following a bolus dose. Similarly, isoproterenol, a B-agonist only, had no significant effect on plasma glucose. Thus, failure to detect an increase in blood glucose when chickens were given physiological levels of catecholamines with b-agonist activities suggests that for this species, at least under the conditions used in the present experiments, P-agonists do not produce measurable glycogenolysis. Therefore, the possibility that blood glucose is not significantly altered by catecholamines in chickens during stress must be considered. Glucagon appears to be the major hormonal glycolytic agent in the chicken, but is not thought to be released by neural mechanisms (Hazelwood, 1986). In contrast to chickens, turkeys showed a progressive rise in plasma glucose levels in response to epinephrine infusion at 2.5 mg/kg/min. Furthermore, an even greater rise in plasma glucose was seen during continuous infusion of isoproterenol. At the time of

62

R. J.

THURSTON et al.

the bolus, levels were already greater than 200% of the T, glucose concentration, so the bolus injection of isoproterenol had little effect on stimulating additional increases in blood glucose. This finding clearly demonstrates that catecholamines, which are B-agonists, can mobilize glucose in the turkey, presumably via glycogenolysis. Grande (1969) reported that infusion of epinephrine into geese also causes plasma glucose levels to rise significantly. Phenylephrine, an a-agonist, did not significantly increase plasma glucose in the chicken, and in the turkey, the only significant effect was a transient increase in plasma glucose following the bolus injection. This is consonant with the understanding that if catecholamines cause glycogenolysis, they have their effect through /?-receptors (Freeman and Manning, 1974). The finding that epinephrine and isoproterenol had no effects on blood glucose levels in chickens was surprising given that these catecholamines have been reported to be glycolytic agents for this species (Langslow et al., 1970; Freeman and Manning, 1974). However, these investigators used pharmacological doses given in an unorthodox manner. Langslow et al. (1970) gave 25 mg of adrenaline intracardially, whereas, Freeman and Manning (1974) administered the catecholamines at a level of 300 pg/kg intraabdominally. Nevertheless, in hepatocytes isolated from chicken embryos, adrenaline (1.1 x 10e5 M) caused glycogenolysis, an effect abolished by the b-blocker propranolol (Picardo and Dickson, 1982). No effect was observed for the cc-agonist, phenylephrine. This data suggests that adrenaline stimulates glycogenolysis in the chicken by /I-receptors. Thus the lack of response of blood glucose to /I-agonists in the present study is an enigma, but the following possibilities are proposed: (a) as for lipogenesis (Harris et al., 1988), the response of hepatocytes to /I-agonists may decline in older birds; and (b) glycogenolysis in the chicken, under physiological conditions, may be relegated to control by the more potent hormone, glucagon (Picardo and Dickson, 1982). In summary, the present experiments have produced evidence that exposure of turkeys to stress may deplete glycogen through sympathetic release of B-agonists, but no effect was observed for the chicken. This may have practical application as the chickens and turkeys used in this study were of the same strain and approximate age as are commercial birds in the United States which are processed for food

production. confounded

However, the results may have been by age differences in the birds. REFERENCES

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