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Plasma glucagon and energy substrate responses of domestic fowl to treadmill exercise
Camp. Biochem.
Physiol. Vol. 86A, No. 2, pp. 209-212,
1987
0300-9629/87
Printed in Great Britain
0
$3.00 + 0.00
1987 Pergamon Journals Ltd
PLASMA GLUCAGON AND ENERGY SUBSTRATE RESPONSES OF DOMESTIC FOWL TO TREADMILL EXERCISE J. H. BRACKENBURY,*
R. VINCENT*
and M. A. MITCHELL?
*Sub-Department of Veterinary Anatomy, University of Cambridge, Cambridge, CB2 lQS, UK. Telephone: (0223)333791 and tAFRC Poultry Research Centre, Roslin, Midlothian EH25 9PS, Scotland, UK (Received
19 May
1986)
Abstract-l. Exercise-induced alterations in the concentrations of plasma glucagon-like immunoreactivity (GLI), plasma free fatty acids (FFA) and blood glucose and lactate were measured in separate groups of male and female domestic fowl. 2. There were only small changes in blood glucose and lactate concentrations but plasma FFA and GLI rose by up to 450 and 200% respectively. There was evidence that the GLI response was stronger at higher exercise intensities. 3. It is suggested that the mobilization of FFA for use as energy substrates by the working muscles may be stimulated by the enhanced secretion of glucagon.
INTRODUCTION In a recent study it was shown that there was a large increase in plasma free fatty acid concentrations (FFA) during prolonged treadmill exercise in domestic fowl (Brackenbury and El-Sayed, 1984). This was consistent with the view that FFA are mobilized as a major energy source for the working muscles. Little is known about the hormonal control of energy metabolism in exercizing birds but the fact that catecholamines have little effect on avian adipocytes whilst glucagon is a potent lipolytic agent (Freeman and Manning, 1974) suggests that there may be considerable differences from exercizing mammals. There is also a strong feedback relationship between avian plasma FFA and glucagon levels (Gross and Mialhe, 1974; Laurent and Mialhe, 1978; Strosser et al., 1983a,b; Foltzer et al., 1985). The primary purpose of the present investigation was therefore to examine whether the mobilization of FFA during treadmill exercise in domestic fowl might be correlated with alterations in plasma glucagon-like immunoreactivity (G.L.I.). MATERIALS AND METHODS The experiments were carried out on separate groups of male (N = 9) and female (N = 11) domestic fowl Gallus domesticus (Light Sussex breed) aged between 6 months and 2 years. The birds were fed ad libitum on a diet of mixed cereals. Each bird was given at least two 40min practice runs on the treadmill before the experiments began. During the training period the birds were placed in small groups in a cage at the end of the moving treadmill and removed one by one in order to take their turn on the treadmill. In this way it was hoped that they would become accustomed to the experimental procedures before the series began. The running surface of the treadmill measured 153 x 40 cm and each long side was guarded by a 1 m high smoked perspex wall. The farther end of the treadmill was closed by the cage containing the birds whilst one of the experimenters
remained seated at the nearer open end of the treadnull throughout each run. During the experiments the birds ran at two different speeds: a “low” speed which could be sustained for at least 70min and a “high” speed which lasted 30min. These speeds were 2.5 and 3.5 km. hrr’ respectively in the females, and 3.5 and 5.0 km. hr-’ respectively in the males. Each bird ran a low speed run for 40 min, then for 70 min, on different occasions. Finally, each bird ran a single 30 min high speed run. Only one run was performed per individual per day. Blood samples were drawn from the brachial vein by venepuncture immediately after each run. In the control experiments blood samples were drawn from birds that had been resting on the stationary treadmill, or had been seated in the cage at the end of the moving treadmill for 70min. Each of these control samples was taken on a different occasion in order to obviate any effect of venepuncture on the measured blood parameters. A 3 ml sample of blood was drawn of which 0.5 ml was placed immediately in ice-cold 0.6 N perchloric acid and used subsequently for lactate analysis. The remainder of the blood was placed in a tube lined with anti-coagulant (EDTA) and centrifuged at 4-5000 rev. min-’ for 15 min. A 0.6 ml sample of plasma was removed and deep frozen for subsequent hormone assay whilst the rest was used for glucose and FFA analysis. Standard enzymatic techniques were used for the measurement of lactate and glucose (Boehringer, Mannheim). Plasma FFA were determined according to the calorimetric method of Falholt et al. (1973). The method for the determination of plasma G.L.I. was as follows. After thawing, all samples were centrifuged to remove precipitated lipoprotein which may interfere with the assay procedure, particularly in plasma from adult female birds. Plasma glucagon-like immunoreactivity (G.L.I.) was determined by means of a heterologous double antibody radioimmunoassay. To prevent degradation of glucagon by plasma proteases Kallikrein inactivator (Trasylol-Bayer Ltd UK) was added at a concentration of 500 KIU ml-’ to all samples. This reagent was also added at the same concentration to the assay incubation mixture. All assay reagents were obtained from Cambridge Medical Diagnostics UK Ltd. The first antibody was raised against porcine pancreatic 209
J. H. BRACKENBURYet al
210
Statistical comparisons paired where appropriate.
glucagon in rabbit. It has a cross reactivity of less than 3% with canine gut G.L.I., less than 1% with porcine glucagon fragment l-26 and less than 1% with jejunal and ileal extracts. The second antibody was goat anti-rabbit gamma globulin. Iiz5 labelled porcine glucagon tracer was made up in normal rabbit serum immediately prior to assay. Purified porcine glucagon was employed as standard. The first incubation was for 24 hr at 4°C. Normal sheep serum was added to all standards and sample tubes prior to addition of second antibody and incubation at 22’C for a further 2 hr. Recovery of porcine glucagon (Eli Lilly Research Laboratories, Indianapolis, Ind.) added to laying hen plasma was 89%. The intra-assay coefficient of variation was 5%. The G.L.I. in plasma from both male and female chickens diluted parallel to the porcine standard as did extracts of chicken pancreas prepared according to Kenny (1955). All results are expressed as ng ml-’ equivalents of porcine glucagon-like immunoreactivity. The values of plasma G.L.I. obtained for control birds in the present study are in close agreement with previous studies in the domestic fowl (Hazelwood and Langslow. 1978; Cramb and Langslow, 1984).
were made using Student’s
RESULTS Exercise at the lower intensity stimulated a 200% increase in plasma FFA concentrations in males and a 40&600% increase in females (Fig. 1). Glucose concentrations generally decreased after exercise but in seven birds out of twenty it increased. The changes in glucose and FFA concentrations between 0 and 40, 0 and 70 and 40 and 70 min of exercise were statistically related (P < 0.02, 0.001 and 0.05, respectively). Lactate concentrations were not significantly affected by exercise in the males but were slightly elevated in the females. G.L.I. concentration showed a sustained 75% increase in the males and a 150% increase in the females, although the latter was not maintained beyond the first 40min. Although G.L.I. and FFA concentrations clearly show the same overall pattern of change (Fig. I), The
Female
T 1.0-
2
0.4
5
2.0
1
;;I
?!
-
+ 0
Ai 20
40 Time, min.
60
r-test,
80
0
20
40 60 Time, min.
80
Fig. 1. Changes in the concentrations of plasma glucagon-like immunoreactivity, free fatty acids (FFA), blood glucose and blood lactate in exercised (filled circles) and control (unfilled circles) birds. Exercise took place at the lower treadmill speed. Mean f 1SE. Data from 9 males and 11females. Asterisks denote values that were significantly different from rest (P I 0.05).
Responses
of domestic
Female
*
fowl to treadmill
Male
exercise
211
Female
1.0 .
z 5 @82 4 0.6 2
0.4-
4: @2hI d.0 -
g
lo-
2.0 ;;
F
1.6 2
-1.2 2 -0.8 5 -0.4 4 -0.0 0 Rest aEnd-Exercise Fig. 2. Concentrations of plasma glucagon-like immunoreactivity, plasma FFA, blood glucose and blood lactate in birds at rest and immediately after 30 min exercise at the higher speed. Mean k 1 SE. Data from 9 males and 1I females. Asterisks denote values that were significantly different from rest (P $0.05).
concentrations at any single time point were not correlated, nor were the magnitudes of the exercise induced changes in these parameters. There were no corresponding correlations between G.L.I. and glucose. The response to exercise at the higher intensity was similar to that measured at the lower intensity, but with an increased magnitude. Blood glucose concentration underwent a significant 20% drop in both sexes (Fig. 2). Lactate again was marginally elevated in the females. G.L.I. levels increased by 150 and 200% in males and females respectively. DISCUSSION
The magnitude of hormonal responses to physical exercise is related not only to the work intensity, but more directly to the fractional work load measured in terms of the maximum oxygen consumption vo’,,,,, (Galbo, 1985). Two work loads were therefore selected in the present study in order to take into accound the effects of exercise intensity on hormonal and energy substrate responses. pojo2max was not measured directly but previous studies had shown that the low and high treadmill speeds corresponded approximately to 6&65% Vo,,,, and 75-85% Vo,,,,, respectively (Brackenbury and El-Sayed, 1985). Although blood lactate concentration rose significantly in the females, the change was marginal compared to the increases previously measured (Brackenbury and El-Sayed, 1985) in females running at faster speeds. It can therefore be inferred that the birds in the present study were producing energy by purely aerobic means. The large increase in plasma FFA concentration during exercise (Figs 1 and 2) is similar to that previously reported (Brackenbury and El-Sayed, 1984) and is consistent with the view that lipid is mobilized and utilized as an important source of
energy and that this takes place within half an hour of the start of running. The observed increase in G.L.I. along with plasma FFA concentration may reflect the well-known lipolytic role of glucagon in birds. However, the absence of any direct correlation between concentrations, or changes in concentrations of plasma G.L.I. and FFA (in individual birds) suggests that the link between the two is not simple. Numerous studies in ducks have demonstrated the existence of a complex feedback relationship between plasma glucagon and FFA (Gross and Miahle. 1974; Laurent and Miahle, 1978; Foltzer et al., 1985; Strosser et al., 1983a,b). Infusion of oleic acid into juvenile ducks produced a decrease in plasma glucagon-like immunoreactivity (Foltzer et al., 1985). On the other hand linoleate stimulated glucagon secretion by isolated chicken pancreatic fragments (Colca and Hazelwood, 1981). In the context of the exercising bird it is possible that a feedback relationship between FFA and glucagon, acting via the inhibition of pancreatic A cell secretion, would help preserve the hormone at a level sufficient to promote lipid mobilization whilst at the same time preventing an over-utilization of glucose. In a study of the endocrine responses of running ducks, Harvey et al. (1982) observed a progressive rise in glucagon concentration coupled with a fall in insulin concentration. It was suggested that these alterations in pancreatic function may have been triggered by augmented catecholamine release and later Rees et al. (1984) measured increased plasma levels of dopamine, adrenaline and noradrenaline in treadmill-exercised chickens. The possibility that increased glucagon secretion may have been caused by hypoglycaemia was discounted since in a related study by Harvey and Phillips (1982) the blood glucose concentration of running ducks did not fall. Similarly in the present study, changes in G.L.I. and glucose concentrations were not linked directly.
212
J. H. BRACKENBURYetal.
Acknowledgements-The work was supported by the Agricultural and Food Research Council (Grant No. AG8/258). We thank Mr I. R. Edgar of the Sub-Department of Veterinary Anatomy for technical assistance. REFERENCES Brackenbury J. H. and El-Sayed M. S. (1984) Changes in plasma glucose and lipid concentrations during treadmill exercise in domestic fowl. Camp. Biochem. Physiol. 79A, 447450. Brackenbury J. H. and El-Sayed M. S. (1985) Comparison of running energetics in male and female domestic fowl. J. exp. Biol. 117, 349-355. Colca J. R. and Hazelwood R. L. (1981) Insulin, pancreatic polypeptide, and glucagon release from the chicken pancreas in vitro: responses to changes in medium glucose and free fatty acid content. Gen. camp. Endocrinol. 45, 482490. Cramb E. and Langslow D. R. (1984) The endocrine pancreas: control of secretions and actions of the hormones In Physiology and Biochemistry of the Domestic Fowl (Edited by Freeman B. M.), Vol. 5, pp. 94124. Academic Press, London. Falhoh K., Lund B. and Falholt W. (1973) An easy calorimetric micro-method for routine determination of free fatty acids in plasma. Clin. chim. Acra 46, 105-l Il. Foltzer Ch., Strosser M. Th., Harvey S. and Mialhe P. (1985) Control of plasma levels of growth hormone, glucagon and insulin in ducklings: roles of free fatty acids and somatostatin. J. Endocr. 106, 21-25. Freeman B. M. and Manning A. C. C. (1974) The prandial
state and the glycaemic and lipolytic responses of Callus domesficus to catecholamines and glucagon. Camp. Biothem. Physiol. 47A, 114551152. Galbo H. (1985) The hormonal response to exercise. Proc. Nutr. Sot. 44, 257-266. Gross R. and Miahle P. (1974) Free fatty acid-glucagon feed-back mechanism. Diabetologia 10, 277-283. _ Harvev S. and Phillios J. G. (1982) Adrenocortical resoonses of ducks to treadmill exercise.‘J. Endocr. 90, 141-146. Harvey S., Klandorf H., Foltzer C., Strosser M. T. and Phillips J. G. (1982) Endocrine responses of ducks (Anas platyrhynchos) to treadmill exercise. Gen. camp. Endocr. 48, 415420. Hazelwood R. L. and Langslow D. R. (1978) Intrapancreatic regulation of hormone secretion in the domestic fowl, Callus domeskus. J. Endocr. 76, 449459. Kenny A. J. (1955) Extractable glucagon of the human pancreas. J. clin. Endocr. Metab. 15,~1089~1105. Laurent F. and Mialhe P. (1978) Effect of free fattv acids and amino acids on glucagon and insulin secretions in normal and diabetic ducks. Diabefologia 15, 313-321. Rees A., Hall R. R. and Harvey S. (1984) Adrenocortical and adrenomedullary responses of fowl to treadmill exercise. Gen. camp. Endocr. 55, 488492. Strosser M. T., Fohzer C., Cohen L. and Mialhe P. (1983a) Evidence for an indirect effect of somatostatin on glucagon secretion via inhibition of free fatty acid release in the duck. Horm. Metabol. Res. 15, 279-283. Strosser M. T., Di Scala-Guenot D., Koch B. and Mialhe P. (1983b) Inhibitory effect and mode of action of somatostatin on lipolysis in chicken adipocytes. Biochim. biophys. Acta 763, 191-196.
Physiol. Vol. 86A, No. 2, pp. 209-212,
1987
0300-9629/87
Printed in Great Britain
0
$3.00 + 0.00
1987 Pergamon Journals Ltd
PLASMA GLUCAGON AND ENERGY SUBSTRATE RESPONSES OF DOMESTIC FOWL TO TREADMILL EXERCISE J. H. BRACKENBURY,*
R. VINCENT*
and M. A. MITCHELL?
*Sub-Department of Veterinary Anatomy, University of Cambridge, Cambridge, CB2 lQS, UK. Telephone: (0223)333791 and tAFRC Poultry Research Centre, Roslin, Midlothian EH25 9PS, Scotland, UK (Received
19 May
1986)
Abstract-l. Exercise-induced alterations in the concentrations of plasma glucagon-like immunoreactivity (GLI), plasma free fatty acids (FFA) and blood glucose and lactate were measured in separate groups of male and female domestic fowl. 2. There were only small changes in blood glucose and lactate concentrations but plasma FFA and GLI rose by up to 450 and 200% respectively. There was evidence that the GLI response was stronger at higher exercise intensities. 3. It is suggested that the mobilization of FFA for use as energy substrates by the working muscles may be stimulated by the enhanced secretion of glucagon.
INTRODUCTION In a recent study it was shown that there was a large increase in plasma free fatty acid concentrations (FFA) during prolonged treadmill exercise in domestic fowl (Brackenbury and El-Sayed, 1984). This was consistent with the view that FFA are mobilized as a major energy source for the working muscles. Little is known about the hormonal control of energy metabolism in exercizing birds but the fact that catecholamines have little effect on avian adipocytes whilst glucagon is a potent lipolytic agent (Freeman and Manning, 1974) suggests that there may be considerable differences from exercizing mammals. There is also a strong feedback relationship between avian plasma FFA and glucagon levels (Gross and Mialhe, 1974; Laurent and Mialhe, 1978; Strosser et al., 1983a,b; Foltzer et al., 1985). The primary purpose of the present investigation was therefore to examine whether the mobilization of FFA during treadmill exercise in domestic fowl might be correlated with alterations in plasma glucagon-like immunoreactivity (G.L.I.). MATERIALS AND METHODS The experiments were carried out on separate groups of male (N = 9) and female (N = 11) domestic fowl Gallus domesticus (Light Sussex breed) aged between 6 months and 2 years. The birds were fed ad libitum on a diet of mixed cereals. Each bird was given at least two 40min practice runs on the treadmill before the experiments began. During the training period the birds were placed in small groups in a cage at the end of the moving treadmill and removed one by one in order to take their turn on the treadmill. In this way it was hoped that they would become accustomed to the experimental procedures before the series began. The running surface of the treadmill measured 153 x 40 cm and each long side was guarded by a 1 m high smoked perspex wall. The farther end of the treadmill was closed by the cage containing the birds whilst one of the experimenters
remained seated at the nearer open end of the treadnull throughout each run. During the experiments the birds ran at two different speeds: a “low” speed which could be sustained for at least 70min and a “high” speed which lasted 30min. These speeds were 2.5 and 3.5 km. hrr’ respectively in the females, and 3.5 and 5.0 km. hr-’ respectively in the males. Each bird ran a low speed run for 40 min, then for 70 min, on different occasions. Finally, each bird ran a single 30 min high speed run. Only one run was performed per individual per day. Blood samples were drawn from the brachial vein by venepuncture immediately after each run. In the control experiments blood samples were drawn from birds that had been resting on the stationary treadmill, or had been seated in the cage at the end of the moving treadmill for 70min. Each of these control samples was taken on a different occasion in order to obviate any effect of venepuncture on the measured blood parameters. A 3 ml sample of blood was drawn of which 0.5 ml was placed immediately in ice-cold 0.6 N perchloric acid and used subsequently for lactate analysis. The remainder of the blood was placed in a tube lined with anti-coagulant (EDTA) and centrifuged at 4-5000 rev. min-’ for 15 min. A 0.6 ml sample of plasma was removed and deep frozen for subsequent hormone assay whilst the rest was used for glucose and FFA analysis. Standard enzymatic techniques were used for the measurement of lactate and glucose (Boehringer, Mannheim). Plasma FFA were determined according to the calorimetric method of Falholt et al. (1973). The method for the determination of plasma G.L.I. was as follows. After thawing, all samples were centrifuged to remove precipitated lipoprotein which may interfere with the assay procedure, particularly in plasma from adult female birds. Plasma glucagon-like immunoreactivity (G.L.I.) was determined by means of a heterologous double antibody radioimmunoassay. To prevent degradation of glucagon by plasma proteases Kallikrein inactivator (Trasylol-Bayer Ltd UK) was added at a concentration of 500 KIU ml-’ to all samples. This reagent was also added at the same concentration to the assay incubation mixture. All assay reagents were obtained from Cambridge Medical Diagnostics UK Ltd. The first antibody was raised against porcine pancreatic 209
J. H. BRACKENBURYet al
210
Statistical comparisons paired where appropriate.
glucagon in rabbit. It has a cross reactivity of less than 3% with canine gut G.L.I., less than 1% with porcine glucagon fragment l-26 and less than 1% with jejunal and ileal extracts. The second antibody was goat anti-rabbit gamma globulin. Iiz5 labelled porcine glucagon tracer was made up in normal rabbit serum immediately prior to assay. Purified porcine glucagon was employed as standard. The first incubation was for 24 hr at 4°C. Normal sheep serum was added to all standards and sample tubes prior to addition of second antibody and incubation at 22’C for a further 2 hr. Recovery of porcine glucagon (Eli Lilly Research Laboratories, Indianapolis, Ind.) added to laying hen plasma was 89%. The intra-assay coefficient of variation was 5%. The G.L.I. in plasma from both male and female chickens diluted parallel to the porcine standard as did extracts of chicken pancreas prepared according to Kenny (1955). All results are expressed as ng ml-’ equivalents of porcine glucagon-like immunoreactivity. The values of plasma G.L.I. obtained for control birds in the present study are in close agreement with previous studies in the domestic fowl (Hazelwood and Langslow. 1978; Cramb and Langslow, 1984).
were made using Student’s
RESULTS Exercise at the lower intensity stimulated a 200% increase in plasma FFA concentrations in males and a 40&600% increase in females (Fig. 1). Glucose concentrations generally decreased after exercise but in seven birds out of twenty it increased. The changes in glucose and FFA concentrations between 0 and 40, 0 and 70 and 40 and 70 min of exercise were statistically related (P < 0.02, 0.001 and 0.05, respectively). Lactate concentrations were not significantly affected by exercise in the males but were slightly elevated in the females. G.L.I. concentration showed a sustained 75% increase in the males and a 150% increase in the females, although the latter was not maintained beyond the first 40min. Although G.L.I. and FFA concentrations clearly show the same overall pattern of change (Fig. I), The
Female
T 1.0-
2
0.4
5
2.0
1
;;I
?!
-
+ 0
Ai 20
40 Time, min.
60
r-test,
80
0
20
40 60 Time, min.
80
Fig. 1. Changes in the concentrations of plasma glucagon-like immunoreactivity, free fatty acids (FFA), blood glucose and blood lactate in exercised (filled circles) and control (unfilled circles) birds. Exercise took place at the lower treadmill speed. Mean f 1SE. Data from 9 males and 11females. Asterisks denote values that were significantly different from rest (P I 0.05).
Responses
of domestic
Female
*
fowl to treadmill
Male
exercise
211
Female
1.0 .
z 5 @82 4 0.6 2
0.4-
4: @2hI d.0 -
g
lo-
2.0 ;;
F
1.6 2
-1.2 2 -0.8 5 -0.4 4 -0.0 0 Rest aEnd-Exercise Fig. 2. Concentrations of plasma glucagon-like immunoreactivity, plasma FFA, blood glucose and blood lactate in birds at rest and immediately after 30 min exercise at the higher speed. Mean k 1 SE. Data from 9 males and 1I females. Asterisks denote values that were significantly different from rest (P $0.05).
concentrations at any single time point were not correlated, nor were the magnitudes of the exercise induced changes in these parameters. There were no corresponding correlations between G.L.I. and glucose. The response to exercise at the higher intensity was similar to that measured at the lower intensity, but with an increased magnitude. Blood glucose concentration underwent a significant 20% drop in both sexes (Fig. 2). Lactate again was marginally elevated in the females. G.L.I. levels increased by 150 and 200% in males and females respectively. DISCUSSION
The magnitude of hormonal responses to physical exercise is related not only to the work intensity, but more directly to the fractional work load measured in terms of the maximum oxygen consumption vo’,,,,, (Galbo, 1985). Two work loads were therefore selected in the present study in order to take into accound the effects of exercise intensity on hormonal and energy substrate responses. pojo2max was not measured directly but previous studies had shown that the low and high treadmill speeds corresponded approximately to 6&65% Vo,,,, and 75-85% Vo,,,,, respectively (Brackenbury and El-Sayed, 1985). Although blood lactate concentration rose significantly in the females, the change was marginal compared to the increases previously measured (Brackenbury and El-Sayed, 1985) in females running at faster speeds. It can therefore be inferred that the birds in the present study were producing energy by purely aerobic means. The large increase in plasma FFA concentration during exercise (Figs 1 and 2) is similar to that previously reported (Brackenbury and El-Sayed, 1984) and is consistent with the view that lipid is mobilized and utilized as an important source of
energy and that this takes place within half an hour of the start of running. The observed increase in G.L.I. along with plasma FFA concentration may reflect the well-known lipolytic role of glucagon in birds. However, the absence of any direct correlation between concentrations, or changes in concentrations of plasma G.L.I. and FFA (in individual birds) suggests that the link between the two is not simple. Numerous studies in ducks have demonstrated the existence of a complex feedback relationship between plasma glucagon and FFA (Gross and Miahle. 1974; Laurent and Miahle, 1978; Foltzer et al., 1985; Strosser et al., 1983a,b). Infusion of oleic acid into juvenile ducks produced a decrease in plasma glucagon-like immunoreactivity (Foltzer et al., 1985). On the other hand linoleate stimulated glucagon secretion by isolated chicken pancreatic fragments (Colca and Hazelwood, 1981). In the context of the exercising bird it is possible that a feedback relationship between FFA and glucagon, acting via the inhibition of pancreatic A cell secretion, would help preserve the hormone at a level sufficient to promote lipid mobilization whilst at the same time preventing an over-utilization of glucose. In a study of the endocrine responses of running ducks, Harvey et al. (1982) observed a progressive rise in glucagon concentration coupled with a fall in insulin concentration. It was suggested that these alterations in pancreatic function may have been triggered by augmented catecholamine release and later Rees et al. (1984) measured increased plasma levels of dopamine, adrenaline and noradrenaline in treadmill-exercised chickens. The possibility that increased glucagon secretion may have been caused by hypoglycaemia was discounted since in a related study by Harvey and Phillips (1982) the blood glucose concentration of running ducks did not fall. Similarly in the present study, changes in G.L.I. and glucose concentrations were not linked directly.
212
J. H. BRACKENBURYetal.
Acknowledgements-The work was supported by the Agricultural and Food Research Council (Grant No. AG8/258). We thank Mr I. R. Edgar of the Sub-Department of Veterinary Anatomy for technical assistance. REFERENCES Brackenbury J. H. and El-Sayed M. S. (1984) Changes in plasma glucose and lipid concentrations during treadmill exercise in domestic fowl. Camp. Biochem. Physiol. 79A, 447450. Brackenbury J. H. and El-Sayed M. S. (1985) Comparison of running energetics in male and female domestic fowl. J. exp. Biol. 117, 349-355. Colca J. R. and Hazelwood R. L. (1981) Insulin, pancreatic polypeptide, and glucagon release from the chicken pancreas in vitro: responses to changes in medium glucose and free fatty acid content. Gen. camp. Endocrinol. 45, 482490. Cramb E. and Langslow D. R. (1984) The endocrine pancreas: control of secretions and actions of the hormones In Physiology and Biochemistry of the Domestic Fowl (Edited by Freeman B. M.), Vol. 5, pp. 94124. Academic Press, London. Falhoh K., Lund B. and Falholt W. (1973) An easy calorimetric micro-method for routine determination of free fatty acids in plasma. Clin. chim. Acra 46, 105-l Il. Foltzer Ch., Strosser M. Th., Harvey S. and Mialhe P. (1985) Control of plasma levels of growth hormone, glucagon and insulin in ducklings: roles of free fatty acids and somatostatin. J. Endocr. 106, 21-25. Freeman B. M. and Manning A. C. C. (1974) The prandial
state and the glycaemic and lipolytic responses of Callus domesficus to catecholamines and glucagon. Camp. Biothem. Physiol. 47A, 114551152. Galbo H. (1985) The hormonal response to exercise. Proc. Nutr. Sot. 44, 257-266. Gross R. and Miahle P. (1974) Free fatty acid-glucagon feed-back mechanism. Diabetologia 10, 277-283. _ Harvev S. and Phillios J. G. (1982) Adrenocortical resoonses of ducks to treadmill exercise.‘J. Endocr. 90, 141-146. Harvey S., Klandorf H., Foltzer C., Strosser M. T. and Phillips J. G. (1982) Endocrine responses of ducks (Anas platyrhynchos) to treadmill exercise. Gen. camp. Endocr. 48, 415420. Hazelwood R. L. and Langslow D. R. (1978) Intrapancreatic regulation of hormone secretion in the domestic fowl, Callus domeskus. J. Endocr. 76, 449459. Kenny A. J. (1955) Extractable glucagon of the human pancreas. J. clin. Endocr. Metab. 15,~1089~1105. Laurent F. and Mialhe P. (1978) Effect of free fattv acids and amino acids on glucagon and insulin secretions in normal and diabetic ducks. Diabefologia 15, 313-321. Rees A., Hall R. R. and Harvey S. (1984) Adrenocortical and adrenomedullary responses of fowl to treadmill exercise. Gen. camp. Endocr. 55, 488492. Strosser M. T., Fohzer C., Cohen L. and Mialhe P. (1983a) Evidence for an indirect effect of somatostatin on glucagon secretion via inhibition of free fatty acid release in the duck. Horm. Metabol. Res. 15, 279-283. Strosser M. T., Di Scala-Guenot D., Koch B. and Mialhe P. (1983b) Inhibitory effect and mode of action of somatostatin on lipolysis in chicken adipocytes. Biochim. biophys. Acta 763, 191-196.