Effect of glucose on plasma glucagon and free fatty acids during prolonged exercise

Summary The effects of glucose ingestion on the changes in blood glucose, FFA, insulin and glucagon levels induced by a prolonged exercise at about 50% of maximal oxygen uptake were investigated. Healthy volunteers were submitted to the following procedures: 1. a control test at rest consisting of the ingestion of 100 g glucose, 2. an exercise test without, or 3. with ingestion of 100 g of glucose. Exercise without glucose induced a progressive decrease in blood glucose and plasma insulin; plasma glucagon rose significantly from the 60th min onward (+45 pg/ml), the maximal increase being recorded during the 4th h of exercise (+135 pg/ml); plasma FFA rose significantly from the 60th min onward and reached their maximal values during the 4th h of exercise (2177±144 ΜEq/l, m±SE). Exercise with glucose ingestion blunted almost completely the normal insulin response to glucose. Under these conditions, exercise did not increase plasma glucagon before the 210th min; similarly, the exercise-induced increase in plasma FFA was markedly delayed and reduced by about 60%. It is suggested that glucose availability reduces exercise-induced glucagon secretion and, possibly consequently, FFA mobilization. Chercheur Qualifié of the Fonds National Belge de la Recherche Scientifique     

Diet induced changes in sympatho-adrenal activity during submaximal exercise in relation to substrate utilization in man

In order to study how the diet may influence sympatho-adrenal activity during exercise, 7 subjects were examined at rest and during submaximal exercise (25 min at 65% of VO2 max) on two occasions. The first occasion was preceded by 5 days on a carbohydrate poor diet (5% carbohydrate, 72% fat and 23% protein) and the second one by 5 days on a carbohydrate rich diet (78% carbohydrate, 8% fat and 14% protein) with the same energy content. Oxygen uptake, respiratory exchange ratio (R), heart rate and arterial plasma concentrations of adrenaline, noradrenaline, dopamine, insulin, glucose, lactate, free fatty acids (FFA), glycerol and beta-hydroxybutyrate were measured at rest and during exercise. Oxygen uptake and heart rate during exercise were higher and R was lower after the carbohydrate poor than after the carbohydrate rich diet. During exercise the arterial plasma concentrations of FFA, glycerol and beta-hydroxybutyrate were higher after the carbohydrate poor than after the carbohydrate rich diet whereas concentrations of insulin and lactate were lower. At rest arterial plasma noradrenaline and adrenaline levels were similar on the two diets (0.70 +/- 0.31 nM noradrenaline and 0.35 +/- 0.32 nM adrenaline one the carbohydrate rich diet, mean values +/- SD). Exercise induced increases in noradrenaline were more pronounced after the carbohydrate poor than after the carbohydrate rich diet (12.42 +/- 3.41 vs. 7.45 +/- 2.68 at 25 min of exercise, p less than 0.001). A similar, although more variable accentuation of exercise induced increases in adrenaline was found. It is concluded that, when compared to a carbohydrate rich diet, a carbohydrate poor diet increases the relative contribution of fat to oxidative metabolism and increases the sympatho-adrenal response to exercise. Stimulation of lipolysis by sympatho-adrenal mechanisms might be of importance for the substrate availability when carbohydrate intake in low.     

Prior endurance exercise attenuates growth hormone response to subsequent resistance exercise

This study examined the influence of prior endurance exercise on hormonal responses to subsequent resistance exercise. Ten males exercised on a cycle ergometer at 50% of maximal oxygen uptake for 60 min and subsequently completed a resistance exercise (bench and leg press, four sets at ten repetitions maximum with an interset rest period of 90 s). Alternatively, the subjects performed the protocol on a separate day with prior endurance exercise limited to 5 min. Blood was obtained before and after the endurance exercise, and 10, 20, and 30 min after the resistance exercise. Maximal isometric torque measured before and after endurance and resistance exercises showed no significant difference between trials. No significant difference was seen in the concentrations of glucose, lactate, testosterone, and cortisol between the trials, but free fatty acids (FFA) and growth hormone (GH) increased (P<0.01 and P<0.05, respectively) after 60 min of endurance exercise. Conversely, after the resistance exercise, GH was attenuated by 60 min of prior exercise (P<0.05). These results indicate that the GH response to resistance exercise is attenuated by prior endurance exercise. This effect might be caused by the increase in blood FFA concentration at the beginning of resistance exercise.     

Utilization of blood-borne and intramuscular substrates during continuous and intermittent exercise in man.

1. Substrate utilization in the legs during bicycle exercise was studied in five subjects when performing intermittent intense exercise (15 sec work--15 sec rest) as well as continuous exercise during 60 min, with an almost identical average power output and oxygen uptake in both situations. 2. Muscle biopsies were obtained from vastus lateralis at rest, during, and after exercise in order to determine intramuscular lipid and carbohydrate utilization. The contribution from blood-borne substrates to total oxidative metabolism was determined by arterial-femoral venous (a-fv) differences for oxygen, FFA, glucose, and lactate and leg blood flow. 3. Intermittent and continuous exercise revealed a similar glycogen depletion and the intramuscular lactate accumulation was rather small. A similar uptake of blood-borne substrate (FFA, glucose) was found in both situations whereas a release of lactate only was observed in intermittent exercise. 4. ATP and CP levels oscillated between work and rest periods in intermittent exercise but were not resynthesized to resting levels at the end of the rest periods. The mainly aerobic energy release during each work period in intermittent exercise is partly caused by myoglobin functioning as an oxygen store; this factor was calculated to be more important than ATP and CP or lactate level oscillations. 5. The metabolic response to intermittent exercise was found to be similar to that found in continuous exercise with approximately the same average power output and oxygen uptake. This indicates that some factor in the intermediary metabolism, for instance citrate, functions as a regulator retarding glycolysis and favouring lipid utilization and an aerobic energy release in intermittent exercise.     

The Effect of Lactate in Canine Subcutaneous Adipose Tissue in Situ1

Fredholm , B. B. The effect of lactate in canine subcutaneous adipose tissue in situ. Acta physiol. scand. 1971. 81. 110–123. Na-L(+)-lactate and Na-pyruvate were administered by intraarterial infusion in canine subcutaneous adipose tissue, perfused with the dogs own blood either at a constant rate from a reservoir or by autoperfusion. The glucose uptake was found to be dependent upon the arterial glucose concentration. Similarly the uptake of lactate and pyruvate increased with increasing arterial concentrations, the latter more rapidly than the former. Infusion of Na-L(+)-lactate below 5 mM and Na-D(—)-lactate (10–11 mM) had no effect on the release of FFA and glycerol upon nerve stimulation (4 cps for 5 to 10 min). On the other hand Na-L(+)-lactate above 10 mM caused a 70 per cent inhibition of the release of FFA without significantly affecting the glycerol release. Na-pyruvate (5 mM) decreased the glycerol output significantly, but increased the FFA release. Neither of the anions had any significant effect on the glucose uptake. Na-lactate was not vasoactive, whereas Na-pyruvate was slightly vasodilator. It is concluded that lactate in concentrations occurring a.g. during muscular exercise and shock is capable of significantly depressing the rate of FFA release upon nerve stimulation by increasing the rate of re-esterification. The finding that lactate and pyruvate had opposite effects on esterification indicates a role of the cytoplasmatic NADH/NAD ratio in determining the rate of esterification.     

Effects of pre-exercise ingestion of carbohydrate on glycaemic and insulinaemic responses during subsequent exercise at differing intensities

The development of rebound hypoglycaemia has been reported after pre-exercise carbohydrate (CHO) ingestion in some studies but not in others. Differences in the experimental design and factors such as the exercise intensity are likely to be responsible for the discrepancies between these studies. Exercise intensity might be a crucial factor since it affects both insulinaemia and glucose uptake. Therefore the aim of the present study was to compare the glycaemic and insulinaemic responses to exercise at different intensities after ingestion of a standardized pre-exercise CHO load. Eight moderately trained subjects consumed 75 g of glucose 45 min prior to 20 min of exercise at 40%, 65% or 80% maximal power output. Blood samples were collected before glucose ingestion, at 15 min intervals at rest and 5 min intervals during exercise. During exercise, measurements of heart rate and breath-by-breath analysis of expired gas were performed continuously. The trials were performed at [mean (SEM)] 55 (1), 77 (1) and 90 (1) percentages maximal oxygen uptake . At the onset of exercise, plasma glucose concentration returned to pre-ingestion levels, while the insulin concentration was more than three times higher than at rest [on average 57 (7) compared to 16 (1) μU·ml^–1). During exercise, plasma glucose concentrations decreased during the first 5 min of exercise and then stabilized in all trials at concentrations that would not be considered to be hypoglycaemic. There were no significant differences in glucose or insulin concentrations between the three trials during exercise. These data suggest that the glycaemic response to ingestion of 75 g of CHO 45 min pre-exercise is similar during exercise of different intensities. Electronic Publication     

Comparison of the effects of pre-exercise feeding of glucose,glycerol and placebo on endurance and fuel homeostasis in man

Summary Six men were studied during exercise to exhaustion on a cycle ergometer at 73% of following ingestion of glycerol, glucose or placebo. Five of the subjects exercised for longer on the glucose trial compared to the placebo trial (p<0.1; 108.8 vs 95.9 min). Exercise time to exhaustion on the glucose trial was longer (p<0.01) than on the glycerol trial (86.0 min). No difference in performance was found between the glycerol and placebo trials. The ingestion of glucose (lg · kg^–1 body weight) 45 min before exercise produced a 50% rise in blood glucose and a 3-fold rise in plasma insulin at zero min of exercise. Total carbohydrate oxidation was increased by 26% compared to placebo and none of the subjects exhibited a fall in blood glucose below 4 mmol · l^–1 during the exercise. The ingestion of glycerol (lg · kg^–1 body weight) 45 min before exercise produced a 340-fold increase in blood glycerol concentration at zero min of exercise, but did not affect resting blood glucose or plasma insulin levels; blood glucose levels were up to 14% higher (p<0.05) in the later stages of exercise and at exhaustion compared to the placebo or glucose trials. Both glycerol and glucose feedings lowered the magnitude of the rise in plasma FFA during exercise compared to placebo. Levels of blood lactate and alanine during exercise were not different on the 3 dietary treatments. These data contrast with previous reports that have indicated glucose feeding pre-exercise produces hypoglycaemia during strenuous submaximal exercise and reduces endurance performance. It appears that man cannot use glycerol as a gluconeogenic substrate rapidly enough to serve as a major energy source during this type of exercise.     

Cardiovascular and metabolic response to adrenaline infusion in weight-losing patients with and without cancer

Fasting is generally accompanied by a decrease in energy metabolism and hormones. On the other hand, indirect evidence has suggested that the response to adrenergic agonists may be maintained or even increased in malnutrition. The present study evaluated whether weight-losing patients with and without cancer have increased plasma concentrations of catecholamines and different responses to intravenously infused adrenaline compared to weight-stable individuals. Eight malnourished cancer and 10 non-cancer patients (11% weight loss) were compared to seven well-nourished and weight-stable patients. Adrenaline was infused i.v. at a rate of 0.005 microgram min-1 kg-1 body weight during 40 min followed by a 40 min rest period (without infusion) and then a final 40 min period with i.v. adrenaline infusion (0.02 microgram min-1 kg-1 body weight). Plasma glycerol concentration at fast was higher in weight-losing patients compared to weight-stable individuals. Whole body oxygen uptake, carbon dioxide production, heart rate and plasma concentrations of free fatty acids (FFA) increased while the mean arterial pressure decreased significantly in response to adrenaline infusion at 0.02 microgram kg-1 min-1 in both weight-losing and weight-stable patients. Adrenaline at 0.005 microgram kg-1 min-1 increased plasma FFA levels by 19% (P less than 0.05) in weight-losing patients while no significant alteration was observed in well-nourished patients. Adrenaline infusion at 0.02 microgram kg-1 min-1 decreased the mean arterial blood pressure and stimulated respiratory gas exchange and heart rate significantly more in weight-losing than in weight-stable patients. The slopes for oxygen uptake, carbon dioxide production, heart rate, plasma FFA and plasma glycerol vs. plasma adrenaline and noradrenaline were all significantly steeper (P less than 0.05-0.01) in malnourished patients than in well-nourished controls. The present study suggests an increased sensitivity to adrenaline in weight-losing patients compared to matched controls with normal nutritional state and stable weight.     

Active recovery and post-exercise white blood cell count, free fatty acids, and hormones in endurance athletes

Strenuous endurance exercise in fasted subjects is accompanied by increased plasma levels of catecholamines, leucocytosis, low insulin, and elevated plasma free fatty acids (FFA). Immediately after such exercise, plasma FFA may rise to high and potentially harmful levels, whereas the white blood cell count (WBCC) rapidly decreases towards or below baseline values. The present work investigated how active recovery (AR) for 15 min at 50% of maximal oxygen consumption ( ), after 60 min of uphill running at 83% of , influenced plasma FFA, lymphocyte, neutrophil, granulocyte, and monocyte count, as well as adrenaline, noradrenaline, insulin and cortisol concentrations until 120 min post-exercise. Thirteen endurance athletes participated in the study [24.2 (3.7) years, 1.82 (0.06) m, 76.7 (7.9) kg and 69.2 (6.8) ml min^–1 kg^–1]. In a randomized order, the subjects completed two sets of strenuous workouts, followed by either AR or complete rest in the supine position (RR). Compared with RR, AR strongly counteracted the rapid increase in plasma FFA 5 min post-exercise. The decreases in neutrophil and monocyte counts post-exercise were nullified by AR, and the cell count stayed above resting values throughout the observation period. AR also counteracted the rapid return of hormone concentration towards baseline levels. It would appear that active recovery at low intensity after strenuous exercise can maintain sufficient adrenergic activation to counteract the post-exercise drop in WBCC. However, in spite of keeping the catecholamine concentration high and insulin levels low, AR can also maintain a low plasma FFA concentration, probably because of the continued use of FFA in muscle. It remains to be elucidated whether the observed high FFA and low WBCC values after RR have a negative effect on health. If so, AR could be a preventive measure. Electronic Publication     

Glucoregulation and hormonal changes during prolonged exercise in boys and girls

A group of 17 children, 8.5–11 years old, performed a 60-min cycle exercise at 60% of maximal oxygen uptake (VO_2max) 2 h after a standardized breakfast. They were 10 young boys (pubertal stage =1) and 7 young girls (pubertal stage 2) of similarVO_2max (respective values were 48.5 ml min^–1 kg^–1, SEM 1.8; 42.1 ml min^–1 kg^–1, SEM 2.4). Blood samples of 5 ml were withdrawn by heparinized catheter, the subjects being in a supine position, 30 min before the test, then after 0, 15, 30 and 60 min of exercise and following 30 min recovery. Haematocrit was immediately measured. Thereafter plasma was analysed for glucose, non-esterified fatty acid, glycerol, catecholamine (noradrenaline, adrenaline), insulin and glucagon concentrations. This study showed two main results. First, the onset of exercise induced a significant glucose decrease (of about 11,4%) in all the children. Secondly, both the glycaemic and the hormonal responses were obviously different according to the sex. In boys only, the initial glucose drop was significantly correlated to the pre-exercise insulin values. Whatever the time, the glycaemic levels and the catecholamine responses were lower in girls than in boys, whereas the insulin values remained higher. However, none of these two hormonal parameters seemed to be really responsible for the lower glucose values in girls. On the one hand, the great individual variability of noradrenaline and adrenaline and differences in their relative intensity at the end of the exercise between boys and girls might contribute to the lower catecholamine levels in girls. On the other hand, the lack of a significant relationship in girls between the glucose decrease after exercise and the pre-exercise insulin values might be explained by a relative insulin insensitivity concomitant with the earlier growth spurt in girls, as demonstrated in subjects at rest by other authors. Finally the mechanisms of all these gender differences remain to be clarified and might be accounted for by a different maturation level in boys and girls.     

Effect of diet on the utilization of blood-borne and intramuscular substrates during exercise in man

20 subjects were studied at rest and during a 25 min submaximal exercise (65% of VO₂ max) on two occasions, the first preceded by a fat rich diet and the second by a carbohydrate rich diet. Oxygen uptake, respiratory exchange ratio (R) and arterial-femoral venous differences for glucose, lactate, β-hydroxybutyrate and FFA (based on the fractional extraction of ³H-palmitate) were measured at rest and during exercise. Changes in intramuscular glycogen, triglyceride and lactate concentrations were determined in muscle biopsies taken before and immediately after exercise form m. quadriceps femoris. R was lower after the fat than after the carbohydrate diet and simultaneously the FFA extraction by the exercising leg was higher. The muscle triglycerides did not changes significantly during exercise after either diet. The glucose extraction was insignificantly greater after the fat diet. The glycogen reduction was numerically smaller after the fat diet, but the difference was uncertain and difficult to evaluate due to a large variation after the carbohydrate diet. However, muscle lactate accumulation and release by the exercising leg was smaller after the fat diet, indicating a slower rate of muscle glycogenosis. It is concluded that a fat rich diet increases the relative contribution of fat to the oxidative metabolism, that this increase, to a great extent, is covered by plasma FFA and that the concomitant decrease in carbohydrate utilization concerns muscle glycogen rather than blood glucose.     

Blood flow, substrate utilization and heat generation in tissues drained by the azygos vein in man

The present study was undertaken to examine the blood flow, heat generation and substrate utilization in tissues drained by the azygos vein in healthy subjects. Catheters were inserted percutaneously into the azygos vein and the pulmonary artery in 10 healthy male subjects in the basal, post-absorptive state. Blood flow in the azygos vein was measured by thermodilution technique, blood temperature was recorded in both the azygos vein and the pulmonary artery and blood samples for the determination of oxygen content and substrate concentrations were collected from both vessels repeatedly at timed intervals. Free fatty acid (FFA) exchange was evaluated following the intravenous infusion of 14-C labelled oleic acid. The average azygos vein blood flow was 94 +/- 10 ml/min. The coefficient of variation for the flow determination was 3.6%. The blood temperature in the azygos vein was consistently higher than that in the pulmonary artery, indicating an average calculated net heat production in the tissues of 0.5 W. The oxygen uptake to the tissues drained by the azygos vein amounted to 6 +/- 1 ml/min. Significant amounts of glucose, FFA and ketone bodies were taken up in the azygos area, while both glycerol and FFA were released. The FFA uptake could, if oxidized, account for about half of the oxygen uptake. In conclusion, the findings indicate that, in the basal state, the tissues drained by the azygos vein utilize both glucose and FFA. Heat is generated within the area but the rate of generation is low and can largely be explained by the oxidative metabolism. The findings do not support an important role for brown adipose tissue metabolism in the interscapular region in man.     

Association between fatigue and failure to preserve cerebral energy turnover during prolonged exercise

AIM: This study evaluated if the fatigue and apathy arising during exercise with hypoglycaemia could relate to a lowering of the cerebral metabolic rates of glucose and oxygen. METHODS AND RESULTS: Six males completed 3 h of cycling with or without glucose supplementation in random order. Cerebral blood flow, metabolism and interleukin-6 (IL-6) release were evaluated with the Kety-Schmidt technique. Blood glucose was maintained during the glucose trial, while it decreased from 5.2 +/- 0.1 to 2.9 +/- 0.3 mmol L-1 (mean +/- SE) after 180 min of exercise in the placebo trial with a concomitant increase in perceived exertion (P < 0.05). During hypoglycaemia, the cerebral glucose uptake was reduced from 0.34 +/- 0.05 to 0.28 +/- 0.04 micromol g(-1) min(-1), while the cerebral uptake of beta-hydroxybutyrate increased to 5 +/- 1 pmol g(-1) min(-1) (P < 0.05). The reduced glucose uptake was accompanied by a lowering of the cerebral metabolic rate of oxygen from 1.84 +/- 0.19 mmol g(-1) min(-)1 during exercise with glucose supplementation to 1.60 +/- 0.16 mmol g(-1) min(-1) during hypoglycaemia (P < 0.05). In addition, the cerebral IL-6 release was reduced from 0.4 +/- 0.1 to 0.0 +/- 0.1 pg g(-1) min(-1) (P < 0.05). CONCLUSIONS: Exercise-induced hypoglycaemia limits the cerebral uptake of glucose, exacerbates exercise, reduces the cerebral metabolic rate of oxygen and attenuates the release of IL-6 from the brain.     

Fat metabolism in brown adipose tissue in vivo

1. Noradrenaline infusions (I.V. for 30 min) in new-born and 1-week-old unanaesthetized rabbits caused a rapid and sustained rise in oxygen consumption and an increase in blood glucose, free fatty acid and glycerol concentrations. Similar changes occurred in anaesthetized 1-week-old rabbits.2. A simple direct method was used to measure the net exchange of metabolites across brown adipose tissue in anaesthetized young rabbits. It was found that the brown adipose tissue of rabbits reared from birth in a thermoneutral environment and studied when their next feed was due took glucose from and released fatty acids and glycerol into the circulation.3. Similar rabbits kept unfed for a further 48 hr in a warm environment released fatty acids and glycerol from their brown adipose tissue at a far greater rate, but the rate of glucose uptake was reduced.4. On the other hand the brown adipose tissue of rabbits kept unfed in a cold environment (20 degrees C) took up circulating free fatty acids as well as glucose and did not release glycerol. The brown adipose tissue of these rabbits was depleted of fat.5. The rate of blood flow through brown adipose tissue and the exchange of all three metabolites increased fourfold during noradrenaline infusion in the three groups of rabbits.6. It is concluded (i) that brown adipose tissue releases significant amounts of fatty acids and glycerol into the circulation and that this contribution is greatly increased with noradrenaline infusion and presumably cold exposure, and (ii) that brown adipose tissue depleted of fat produces heat by drawing free fatty acids as well as glucose from the circulation.     

An acute oral dose of caffeine does not alter glucose kinetics during prolonged dynamic exercise in trained endurance athletes

This study investigated the possible influence of oral caffeine administration on endogenous glucose production and energy substrate metabolism during prolonged endurance exercise. Twelve trained endurance athletes [seven male, five female; peak oxygen consumption ( ) = 65.5 ml·kg^–1·min^–1] performed 60 min of cycle ergometry at 65% twice, once after oral caffeine administration (6 mg·kg^–1) (CAF) and once following consumption of a placebo (PLA). CAF and PLA were administered in a randomized double-blind manner 75 min prior to exercise. Plasma glucose kinetics were determined with a primed-continuous infusion of [6,6-²H]glucose. No differences in oxygen consumption ( ), and carbon dioxide production ( ) were observed between CAF and PLA, at rest or during exercise. Blood glucose concentrations were similar between the two conditions at rest and also during exercise. Exercise did lead to an increase in serum free fatty acid (FFA) concentrations for both conditions; however, no differences were observed between CAF and PLA. Both the plasma glucose rate of appearance ( ) and disappearance ( ) increased at the onset of exercise (P<0.05), but were not affected by CAF, as compared to PLA. CAF did lead to a higher plasma lactate concentration during exercise (P<0.05). It was concluded that an acute oral dose of caffeine does not influence plasma glucose kinetics or energy substrate oxidation during prolonged exercise in trained endurance athletes. However, CAF did lead to elevated plasma lactate concentrations. The exact mechanism of the increase in plasma lactate concentrations remains to be determined. Electronic Publication     

Greater serum GH response to arm than to leg exercise performed at equivalent oxygen uptake

Summary The aim of this study was to provide information concerning the mechanism of exercise-induced stimulation of growth hormone (GH) release in human subjects. For this reason serum GH as well as some hemodynamic variables and blood concentrations of noradrenaline (NA), insulin (IRI), lactate (LA), glucose (BG), and free fatty acids (FFA) were determined in seven healthy male subjects exercising on a bicycle ergometer with arms or legs and running on a treadmill at equivalent oxygen consumption levels. Significantly greater increases in serum GH concentration accompanied arm exercises than those observed during the leg exercises. This was accompanied by greater increases in heart rate, blood pressure, and plasma NA and blood lactate concentrations. Serum IRI decreased during both leg exercises and did not change during the arm exercise. There were no differences in BG and plasma FFA concentrations between the three types of exercise. The role of humoral and neural signals responsible for the greater GH response to arm exercise is discussed. The findings are consistent with the hypothesis that neural afferent signals sent by muscle “metabolic receptors” participate in the activation of GH release during physical exercise. It seems likely that the stimulation of these chemoreceptors is more pronounced when smaller muscle groups are engaged at a given work load. However, a contribution of efferent impulses derived from the brain motor centres to the control system of GH secretion during exercise is also possible. This work was partly supported by the Polish Academy of Sciences (project 10.4), and performed within the Scientific Exchange Programme between Medical Research Centre, Polish Academy of Sciences and Institute of Experimental Endocrinology, Slovak Academy of Sciences     

Effect of diet on muscle glycogen and blood glucose utilization during a short-term exercise in man

7 subjects were studied at rest and during a 6 min submaximal exercise (65% of Vo₂, max) on two occasions, the first preceded by a fat rich diet and the second by a carbohydrate rich diet. Oxygen uptake and respiratory exchange ratio (R) were measured at rest and heart rate both at rest and during exercise. Arterial-femoral venous differences for oxygen, glucose, lactate and β-hydroxybutyrate and arterial concentrations of free fatty acids were measured at rest and during exercise. Changes in muscle glycogen (in 6 subjects) and lactate concentration were determined by biopsies from m. quadriceps femoris taken before and immediately after exercise. Muscle glycogen decreased less during exercise after the fat than after the carbohydrate diet in 5 of the 6 subjects, whereas blood glucose extraction by the exercising legs did not change with diet. Muscle lactate accumulation and release were smaller after the fat diet. In conclusion, the muscle glycogen utilization during a short-term exercise appeared to be lower after the fat than after the carbohydrate diet, but not the concomitant blood glucose extraction. These differences between diets were similar to those observed after a more prolonged work at the same load.     

Plasma FFA responses to prolonged walking in untrained men and women

Summary Gender differences in plasma FFA responses to 90 min of treadmill walking at 35% were investigated in six men and six women following an overnight fast. The subjects represented average values for maximal oxygen uptake and body fat percentage for age and gender. Mean plasma FFA concentration at 45 and 90 min of exercise were significantly (P<0.05) higher for women (0.82 mmol·l^–01, 0.88 mmol·l^–01) than men (0.42 mmol·l^–01, 0.59 mmol·l^–1). Lower R values for women throughout the exercise period indicated a greater percentage fat in total metabolism than for men while the FFA/glycerol results supported greater lipolytic activity for women. The uniformity of percent fat in metabolism for women from rest to exercise showed that FFA release from adipose tissue increased rapidly with the onset of exercise which was not the case for men. Comparison of metabolic data as well as a statistical analysis (ANCOVA) controlling for the influence of and percentage body fat on FFA plasma concentration suggested that gender differences in FFA responses to prolonged submaximal exercise can be expected to occur in untrained subjects.     

Effect of adrenaline on exchange of glucose in leg tissues and splanchnic area. A comparison with the metabolic response to surgical stress

Surgical trauma is accompanied by increased energy expenditure and raised arterial concentrations of adrenaline and glucose. In order to study the acute effects of an adrenaline infusion on glucose metabolism and oxygen uptake in the leg and splanchnic bed, adrenaline was administered at a rate giving plasma concentrations of adrenaline similar to those in connection with abdominal surgery. Seven healthy males participated in the study. Adrenaline 40 ng/(min X kg body weight) (0.22 nmol/(min X kg body weight] was infused producing a plasma concentration of 2.77 +/- 0.42 nmol/l (mean +/- SEM). Leg and splanchnic blood flows and the femoral and hepatic arterio-venous differences for oxygen, glucose, lactate and other metabolites were determined. Measurements were made before and between 30 and 40 min after the start of the adrenaline infusion. Following the infusion of adrenaline the leg blood flow increased by 140% and hepatic blood flow by 25%. The leg oxygen uptake increased by 30%, but no significant increase in splanchnic oxygen uptake was observed. The arterial glucose concentration rose by 35%. Splanchnic glucose output increased X 2.5, but no significant increase in leg glucose uptake was observed. Leg release of gluconeogenic substrates increased but only lactate and glycerol uptake increased in the splanchnic bed. Leg blood flow increased more than that usually seen after surgery, whereas leg oxygen uptake and splanchnic oxygen uptake was higher in the immediate postoperative period. Splanchnic glucose release increased more during the infusion than in connection with surgery. It is concluded that adrenaline at a plasma concentration similar to that during and immediately after surgery can induce changes in glucose metabolism which are of the same order or more pronounced than those seen in connection with abdominal surgery.     

Glucose uptake in relation to metabolic state in perfused rat hind limb at rest and during exercise

Summary A modified rat hindlimb perfusion technique, aimed at studying factors of importance for glucose uptake at rest and during exercise, is presented. The modifications involved cannulation of the femoral artery and femoral vein in the groin, instead of the aorta and caval vein. This modification gives a number of advantages, among others the possibility of using the contralateral leg as control, perfused or nonperfused.The muscle tissue was well preserved after 40 min of perfusion, as judged from normal levels of muscle metabolites. The glucose uptake at rest was dependent on glucose delivery (glucose concentration times blood flow) as well as insulin concentration. During exercise, induced by sciatic nerve stimulation, glucose uptake, lactate production and oxygen uptake increased. The glucose uptake during exercise was closely related to the metabolic state of the muscle tissue. Thus, the glucose uptake was negatively correlated with the ATP/ADP ratio and the creatine phosphate level, and positively correlated to the lactate level in both soleus and gastrocnemius muscle. The results suggest that the level of the glucose uptake in exercising muscles is determined by the energy state of the muscle tissue.Supported by grants from the Canadian Medical Research Council and Swedish Medical Research Council (project No 536)