Blood flow distribution during graded treadmill exercise in domestic cockerels.

1. White Leghorn cockerels were exercised continuously for 45 minutes on a treadmill at work loads equivalent to 2.1 and 2.7 times pre-exercise metabolic rates, the latter being close to the performance limits of the experimental birds. 2. Relative blood flow to the abdominal viscera and selected leg muscles was estimated using 113Sn-, 153Gd- and 46Sc-labelled microspheres, injected into the root of the aorta. 3. There was no significant shift of blood flow away from the viscera towards the leg muscles at either work load. However, relative colonic and duodenal blood flow fell significantly at both work loads and relative pancreatic blood flow doubled at the higher work load. 4. It is concluded that, as previously reported in female domestic fowl performing physical exercise close to their performance limits, male fowl are largely refractory to shifts in blood flow away from the viscera to the working muscles. Nevertheless, there is evidence of blood flow shifts between visceral organs, probably related to the intermediary metabolism of fuel substrates.

Effect of acute heat exposure on triglyceride transfer to the preovulatory follicles of the laying fowl (Gallus domesticus).

1. The effect of acute heat exposure on triglyceride (TG) transfer to preovulatory follicles was studied in the laying fowl. 2. Heat exposure of laying fowl resulted in a 1.1 degree C rise in body temperature, a 10-fold increase in respiration frequency and mild hypocapnia and hypoxaemia. 3. Plasma and follicular tissue TG concentrations were not significantly affected by heat exposure, but plasma TG specific radioactivity decreased significantly and was negatively correlated with body temperature. 4. The transfer rate of TG to the preovulatory follicles was not affected significantly by hyperthermia. 5. We conclude that nutrient supply to the developing follicles is not compromised in acutely heat-exposed laying fowl.

Age and exercise effects on mitochondrial density and capillary fibre ratio in bird leg muscle.

1. Muscle fibre composition, capillary-fibre ratio and mitochondrial density of the Iliotibialis lateralis muscle were monitored during growth from the age of 8 weeks to sexual maturity (24 weeks) in sedentary birds and in birds subjected to regular treadmill exercise. 2. The Iliotibialis lateralis muscle consists almost exclusively of type IIA and IIB fibres with a small percentage of "unclassified" fibres. Over the 16-week period of growth there was no change in fibre composition but a marked fibre hypertrophy linked with a fall in the capillary-fibre ratio. Mitochondrial volume density increased with age but this was not significant. 3. Exercise significantly increased the IIA:IIB fibres ratio from 0.77 to 1.1 but had no significant effect on any other measured characteristics. 4. It is concluded that exercise at the intensity and duration employed (10-15 min daily, ca. 70-80% maximum oxygen consumption) has little effect on the growth and development of avian skeletal muscle although there was evidence of an increased oxidative capacity of the muscle.

Respiratory responses of domestic fowl to hyperthermia following selective air sac occlusions.

Ventilation together with blood and respiratory gas tensions were measured in adult domestic fowl under normothermic and hyperthermic conditions, following bilateral occlusion of the cranial and caudal thoracic air sacs (series I) or the cranial and caudal thoracic plus the abdominal air sacs (series II). Series I birds showed no significant differences from controls. Both control and experimental animals displayed a typical thermal polypnoea combined with mild hypocapnaemia. A larger drop in PCO2 was demonstrated in the clavicular sac than in the blood, possibly indicating partial failure of inspiratory valving at the ventrobronchi. However, there was no evidence of any effect of thoracic air sac occlusion on inspiratory airflow valving in the palaeopulmo. Series II birds were strongly hypercapnaemic/hypoxaemic in normothermic conditions, with a normal minute volume, but a faster, shallower breathing pattern. During hyperthermia they increased minute ventilation 3-fold, as in control animals, and blood gas tensions were almost restored to normal. Again, there was no evidence that experimental reduction in air sac capacity, in this case up to 70% of the total, had any effect on inspiratory airflow valving in the palaeopulmo, although inevitably in this case airflow in the neopulmo was abolished.

Effects of treadmill exercise on the distribution of blood flow between the hindlimb muscles and abdominal viscera of the laying fowl.

1. Blood flow distribution between the abdominal viscera and the leg muscles of regularly-laying Rhode Island Red hens was measured at rest and immediately following treadmill exercise, using the radioactive microsphere technique. 2. Exercise brought about a 150% increase in metabolic rate and this was maintained continuously for 90 min. 3. Although there was a small shift in blood flow distribution towards the hindlimb muscles at the expense of the kidneys and reproductive organs, this was not statistically significant. 4. There was a significant reduction in blood flow to the preovulatory follicles of the ovary during exercise, relative to the rest of the abdominal viscera. 5. It is concluded that exercise of this intensity is insufficient to bring about gross changes in blood flow distribution between the abdominal viscera and the hindlimb muscles. The implications of this finding are discussed in relation to the nutrient and blood flow requirements of the reproductive organs.

Treadmill exercise training increases the oxidative capacity of chicken iliotibialis muscle.

The number of fibers staining for the oxidative enzyme succinic dehydrogenase (SDH) was measured in the iliotibialis lateralis caudalis muscle of the domestic fowl before treadmill training and after 6 wk and 15 wk of training, respectively. This leg muscle contains exclusively fast-twitch or type II fibers, and before exercise training approximately 40% of these stained intensely for SDH. After 6 and 15 wk training this proportion rose to approximately 50 and 60%, respectively. Most of these highly oxidative fibers also stained weakly for the glycolytic enzyme alpha-glycerophosphate dehydrogenase (alpha-GPDH) and belonged to the fast-twitch oxidative category. Most of the poorly oxidative fibers stained strongly for alpha-GPDH and therefore belonged to the fast-twitch glycolytic category. It is concluded that exercise training in birds can bring about adaptive changes in the oxidative capacity of skeletal muscle similar to those that have been observed in man and other mammals.

Effects of moderate intensity treadmill exercise on triglyceride production in the laying fowl.

1. Sustained aerobic exercise in domestic fowl has previously been shown to enhance lipid utilization by the skeletal muscles. The present study examined the possibility that such increased lipid oxidation in the laying female might lower the production of plasma triglycerides destined for transfer to the developing oocytes. 2. Following an intravenous injection of 25 muCi of 14C-labelled glycerol trioleate, the experimental birds performed 90 min of treadmill exercise at a work intensity approximately equivalent to 2.5 times the resting metabolic rate. 3. There was no evidence of either glycogen or triglyceride depletion in either the leg muscles or the viscera of the exercised birds. The specific activity of triglyceride TG-SRA found in the tissues was also the same in control and experimental birds. The time-course of the changes in plasma TG-SRA throughout the experimental period gave no indication that TG production had been affected by exercise. 4. It is concluded that the increased energy substrate demand arising from moderate-intensity, aerobic exercise is almost fully met by the liberation of fatty acids from adipose tissue TG stores, and has minimal impact on the hepatic manufacture of egg lipids.

Effects of treadmill exercise on the transfer of plasma triglyceride into the ovary of the laying fowl.

1. The effects of 90 min continuous treadmill exercise on the plasma-to-ovary transfer of 14C-labelled triglycerides in laying hens were examined. 2. Exercised birds showed a 4-fold increase in plasma free fatty acid concentration, a 15% decrease in plasma glucose concentration and unchanged plasma triglyceride concentration compared with resting controls. The mean plasma-to-ovary triglyceride transfer rate was approximately halved by exercise. 3. The surface area-specific triglyceride transfer rate was greatest for oocytes weighing 0.25-1.5 g and decreased with increasing oocyte size. The lowest rates were in the small (less than 0.25 g) white oocytes. This pattern was largely unaffected by exercise. 4. Factors that might be responsible for the reduction in triglyceride transfer into the oocytes during exercise include hormonal effects on the permeability of the oocyte envelope, increased competition for plasma lipids by the working muscles and reduced blood flow to the ovary, as a result of the release of vasoconstrictors.

Utilisation of energy substrates in treadmill-exercised domestic fowl (Gallus gallus domesticus): blood glucose.

1. Blood glucose concentration, glucose turnover and gas exchange were monitored in adult male domestic fowl at rest and during 90 min of continuous treadmill exercise. 2. During exercise oxygen consumption increased to about three times its resting value. Blood glucose concentration fell by 26% by the end of exercise. 3. Blood glucose turnover was not altered by exercise and oxidation showed only a moderate increase (35%). Glucose oxidation accounted for 23% of the total energy expenditure at rest and this value fell to 10% during exercise. At the same time the plasma free fatty acid concentration rose to three times its resting value suggesting an increased mobilisation of this substrate. 4. It is concluded that during exercise of this relatively moderate intensity glucose is a quantitatively minor fuel for the working muscles.

Utilisation of energy substrates in treadmill-exercised domestic fowl (Gallus gallus domesticus): blood plasma free fatty acids.

1. Plasma free fatty acid (FFA) concentration, FFA turnover and gas exchange were measured in adult male domestic fowl at rest and during 90 min continuous treadmill exercise at a work load of approximately three times the resting metabolic rate. 2. Plasma FFA concentration and turnover increased 7-fold and 4-fold respectively during exercise. Of the FFA turnover 0.54 was oxidised at rest and this increased to 0.70 during exercise. The fraction of the total carbon dioxide production derived from plasma FFA oxidation rose from 0.33 at rest to 0.55 during exercise. 3. It is concluded that plasma FFA are the most important source of energy for the working muscles of domestic fowl during treadmill exercise of this intensity and duration.

Sexual maturity and physical exercise alter fibrinolytic activity in birds (chickens).

1. Sexual maturity in the domestic hen is accompanied by hyperlipidaemia. This study examined effects of hyperlipidaemia on fibrinolytic activity at rest and following prolonged treadmill exercise. 2. In immature hens the mean pooled-plasma fibrinolytic activity was 50 mm2 and following 90 min continuous exercise this rose to 114 mm2. In contrast, fibrinolytic activity in mature hens was undetectable but rose to 51 mm2 after exercise. 3. The fibrinolytic response of mature and immature cocks was comparable to that of the immature hens. 4. The resting plasma triglyceride concentration in mature hens was approximately seven times that of the immature hens, immature and mature cocks. Exercise induced significant increases in plasma non-esterified fatty acid concentrations but had no significant effect on triglyceride or cholesterol levels. 5. The results demonstrate that prolonged exercise in birds, as in man, evokes hyperfibrinolysis. However, the response is impaired in mature females and this may be associated with increased blood lipid levels.

Plasma free fatty acid profile in male and female domestic fowl at rest and after exercise.

The concentration and profile of the plasma free fatty acid (FFA) pool was determined in three male and three female domestic fowl before and after a 70 min treadmill run. The fatty acid profile of total food lipids was also determined. At rest, palmitic, stearic oleic, and linoleic acids were the main individual fatty acids in the plasma FFA pool and together constituted 50 to 60% of the total. Shorter chain fatty acids (C10 to C15) made up 24 to 38% of the total. In food lipids C16 and C18 fatty acids constituted more than 95% of total fatty acids, therefore food was not a significant direct source of short chain (less than C16) fatty acids. After exercise, there was an 8 to 10 fold increase in plasma FFA concentration. The proportion of lower chain (less than C16) FFA decreased and the proportion of C16 and C18 FFA, in particular oleic acid, increased. At the end of exercise the profile of the plasma FFA pool was similar to that of the adipose tissue triglyceride. Release of fatty acids from adipose tissue may be a major influence on exercise-induced changes in the plasma FFA profile.

Plasma glucagon and energy substrate responses of domestic fowl to treadmill exercise.

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. 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. 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.

Blood gases and respiratory pattern in exercising fowl: comparison in normoxic and hypoxic conditions.

Clavicular air sac pressure, arterial blood gases and pH, and rectal temperature were measured in treadmill-exercised cockerels breathing air, 10% O2 in N2 or a mixture of 10% O2/3% CO2 in N2. Air sac pressures were used to estimate changes in the rate and the relative depth of breathing. In air-breathing conditions exercise took place at two intensities corresponding to treadmill speeds of 3.2 and 5.0 km h-1, respectively. Rectal temperature increased by 0.5 degrees C but there was no sign of thermal hyperventilation and arterial PCO2 remained constant. Increased ventilation was mainly brought about by changes in respiratory rate, with relatively small increases in depth. During exercise at 3.2 km h-1 inhalation of 10% O2 in N2 produced a 35% increase in ventilation and breathing became faster and shallower. Arterial PCO2 fell by 3-4 Torr, apparently as a result of lung hyperventilation. Addition of 3% CO2 to the hypoxic gas restored normal arterial PCO2 and reversed the trend to polypneic breathing. However, it failed to produce an exact matching of respiratory characteristics with those observed during isocapnic exercise hyperpnea. It is concluded that rapid, shallow breathing during hypocapnic hypoxia in running birds serves as a mechanism to minimize lung hyperventilation and CO2 washout. This reflex, which may stem from the intrapulmonary CO2 receptors, occurs in the face of a severe hypoxic challenge. Failure to match respiratory characteristics during isocapnic hypoxia and isocapnic exercise may be due to an inhibitory effect of the inhaled CO2 on these receptors.

Exercise hyperpnea in birds: evidence against a primary role for pCO2.

Ventilatory responses of domestic fowl to graded intensities of treadmill exercise were compared when the birds breathed air, 3% CO2 in air or 4.2% CO2 in air. During exercise in air, increased minute ventilation resulted mainly from increased respiratory rate with little change in tidal volume. This pattern of ventilatory response was not altered when the birds respired CO2. In contrast, the pattern of ventilatory response to CO2, at given work loads, consisted of a primary increase in tidal volume with little change in respiratory rate. It is concluded that intrapulmonary pCO2 does not affect the ventilatory response to exercise.

Comparison of running energetics in male and female domestic fowl.

Carbon dioxide production (VCO2) and end-exercise venous lactate concentration were compared in intensively-trained, mature male and female domestic fowl running on a treadmill for 10-min periods at maximal and sub-maximal work loads. The relationship between VCO2 and running speed was linear and had the same slope in male and female birds. However the maximum sustainable running speed of the males was approximately twice that in the females and the maximum weight-specific VCO2 was 60% higher in males. End-exercise venous lactate concentration rose significantly above resting at work loads above 75% maximum in females, but only at work loads above 95% maximum in fully-trained males. The results indicate a greater work capability in male than in female birds in the conditions of the experiments.

Respiratory metabolism of D[U-14C]glucose in hens and cocks during prolonged treadmill exercise.

1. The specific activity of expired 14CO2 was measured at rest and during 90 min treadmill exercise following an initial intravenous injection of D[U-14C]glucose. 2. The rate of CO2 production rose 4.5-fold during exercise in cocks but only 2.5-fold in females. The mean respiratory quotient was close to unity at rest and during exercise. 3. Estimated glucose turnover rate rose approximately 3.5-fold during exercise in cocks. Turnover rate did not increase in hens but the fraction of the glucose turnover oxidized to provide energy for the working muscles was increased. 4. It is concluded that carbohydrate sources account for the major fraction of energy expenditure during exercise of this magnitude and duration.

Vagal control of respiratory pattern during hyperpnea in domestic fowl.

Minute volume, tidal volume, and respiratory frequency were measured during hyperpnea induced by exercise, increased body temperature, and CO2 inhalation. Ventilatory characteristics were compared before and after the vagus nerve had been blocked. In normal birds exercise produced increases in both tidal volume and respiratory frequency; hyperthermia produced a typical thermal polypnea consisting of greatly increased respiratory frequency and reduced tidal volume; CO2 inhalation produced increases in tidal volume and respiratory frequency when the birds were euthermic but a slowing of respiratory rate when the birds were hyperthermic. After vagal block these pronounced differences in the pattern of ventilatory response to the various respiratory stimuli were abolished. Instead there was a uniform ventilatory response to all three stimuli consisting mainly of increases in tidal volume combined with small increases in respiratory frequency. It is concluded that in the normal animal control of the varied pattern of ventilatory response to different respiratory stimuli is dependent on vagal fiber activity.