Diurnal variations of serum erythropoietin in trained and untrained subjects

The diurnal variations of serum-erythropoietin concentration ([s-EPO]) were investigated in six physically trained (T) and eight untrained (UT) men. The T subjects had a higher mean maximal oxygen uptake than UT subjects [75.7 (SEM 1.6) ml · min^–1 · kg^–1 versus 48.3 (SEM 1.4) ml · min^–1 · kg^–1, P < 0.0001] and a lower mean body mass index [BMI, 21.7 (SEM 0.7) kg · m^–2 versus 24.4 (SEM 0.6) kg · m^–2, P=0.02]. Each subject was followed individually for 24 h as they performed their normal daily activities. Venous blood samples were collected from awakening (0 min) until the end of the 24-h period (1440 min). Both T and UT had a nadir of [s-EPO] 120 min after awakening [10.0 (SEM 0.3) U · 1^–1 versus 11.5 (SEM 2.1) U · 1^–1, P > 0.05]. The UT and T increased their [s-EPO] to peak values at 960 min and 960–1200 min, respectively (ANOVA P=0.03) after awakening [UT: 18.4 (SEM 2.8) U · l^–1; T: 16.2 (SEM 2.5) U · l^–1, P > 0.05]. The mean 24-h [s-EPO] were 14.5 (SEM 1.0) U · l^–1 and 14.9 (SEM 0.9) U · l^–1 in T and UT, respectively (P > 0.05). The individual mean 24-h [s-EPO] were not correlated to body mass, BMI or maximal oxygen uptaken. Significant diurnal variations in [s-EPO] occurred in these healthy subjects irrespective of their levels of physical activity.     

Caffeine increases maximal anaerobic power and blood lactate concentration

Summary The aim of this study was to specify the effects of caffeine on maximal anaerobic power (W _max). A group of 14 subjects ingested caffeine (250 mg) or placebo in random double-blind order. TheW _max was determined using a force-velocity exercise test. In addition, we measured blood lactate concentration for each load at the end of pedalling and after 5 min of recovery. We observed that caffeine increasedW _max [964 (SEM 65.77) W with caffeine vs 903.7 (SEM 52.62) W with placebo;P<0.02] and blood lactate concentration both at the end of pedalling [8.36 (SEM 0.95) mmol · l^–1 with caffeine vs 7.17 (SEM 0.53) mmol · l^–1 with placebo;P<0.011 and after 5 min of recovery [10.23 (SEM 0.97) mmol · l^–1 with caffeine vs 8.35 (SEM 0.66) mmol · l^–1 with placebo;P<0.04]. The quotient lactate concentration/power (mmol · l^–1 · W^–1) also increased with caffeine at the end of pedalling [7.6 · 10^–3 (SEM 3.82 · 10^–5) vs 6.85 · 10^–3 (SEM 3.01 · 10^–5);P<0.01] and after 5 min of recovery [9.82·10^–3 (SEM 4.28 · 10^–5) vs 8.84 · 10^–3 (SEM 3.58 · 10^–5);P<0.02]. We concluded that caffeine increased bothW _max and blood lactate concentration.     

Sustained noradrenaline sulphate response in long-distance runners and untrained subjects up to 2 h after exhausting exercise

Summary We investigated the response of plasma and platelet free catecholamine ([CA]) and sulphated catecholamine ([CA-S]) concentrations after an incremental treadmill test to exhaustion and during recovery. In triathletes (n = 9) plasma and platelet [CA] and [CA-S] were measured before, immediately after and 0.5 and 24 h after exercise. In long-distance runners (n = 9) and in controls (n = 10) plasma [CA] and [CA-S] were determined 2 h instead of 24 h after exercise. Platelet [CA] and [CA-S] remained unchanged throughout the study. Plasma [CA] increased after exercise in all groups (P<0.05) and returned to pre-exercise values within 0.5 h of recovery. Plasma sulphoconjugated noradrenaline concentration ([NA-S]) was elevated after exercise in the triathletes, long-distance runners and in controls [9.96 (SEM 0.84) nmol·1^–1, 11.8 (SEM 1.19) nmol·1^–1, 9.53 (SEM 1.10) nmol·l^–1, respectively;P<0.05] compared with resting values [7.13 (SEM 1.04) nmol·l^–1, 6.19 (SEM 0.56) nmol·l^–1, 6.76 (SEM 0.67) nmol·1^–1, respectively] and remained elevated after 0.5 h of recovery [9.94 (SEM1.14) nmol·l^–1, 10.96 (SEM 0.80) nmol·l^–1, 8.95 (SEM 0.99) nmol·l^–1, respectively;P<0.05]. In the long-distance runners and controls plasma [NA-S] remained elevated during 2 h of recovery [9.96 (SEM 0.76) nmol·l^–1, 9.03 (SEM 0.88) nmol·l^–1, respectively]. These results would indicate that plasma [NA-S] increases after sympathetic nervous system activation by an exhausting incremental exercise test and remain elevated up to 2 h after exercise.     

Effects of glucose ingestion or glucose infusion on fuel substrate kinetics during prolonged exercise

To determine if bypassing both intestinal absorption and hepatic glucose uptake by intravenous glucose infusion might increase the rate of muscle glucose oxidation above 1 g · min^–1, ten endurance-trained subjects were studied during 125 min of cycling at 70% of peak oxygen uptake (VO_{2 peak}). During exercise the subjects ingested either a 15 g · 100 ml^–1 U-¹⁴C labelled glucose solution or H₂O labelled with a U-¹⁴C glucose tracer for the determination of the rates of plasma glucose oxidation (Rox) and exogenous carbohydrate (CHO) oxidation from plasma¹⁴C glucose and¹⁴CO₂ specific activities, and respiratory gas exchange. Simultaneously, 2-³H glucose was infused at a constant rate to measure glucose turnover, while unlabelled glucose (25% dextrose) was infused into those subjects not ingesting glucose to maintain plasma glucose concentration at 5 mmol · l^–1. Despite similar plasma glucose concentrations [ingestion 5.3 (SEM 0.13) mmol · l^–1; infusion 5.0 (0.09) mmol · l^–1], compared to glucose infusion, CHO ingestion significantly increased plasma insulin concentrations [12.9 (1.0) vs 4.8 (0.5) mU · l^–1;P<0.05], raised total Rox values [9.5 (1.2) vs 6.2 (0.7) mmol · 125 min^–1 kg fat free mass^–1 (FFM);P<0.05] and rates of CHO oxidation [37.2 (2.8)vs 24.1 (3.9) mmol · 125 min^–1 kg FFM^–1;P<0.05]. An increased reliance on CHO metabolism with CHO ingestion was associated with a decrease in fat oxidation. Whereas the contribution from fat oxidation to energy production increased to 51 (10)% with glucose infusion, it only reached 18 (4)% with glucose ingestion (P<0.05). Despite these differences in plasma insulin concentration and rates of fat oxidation, the rates of glucose oxidation by muscle were similar after 125 min of exercise for both trials [ingestion 93 (8); infusion 85 (5) mol · min^–1 kg FFM^–1], suggesting that peak rates of muscle glucose oxidation were primarily dependent on blood glucose concentration which, in turn, regulated the hepatic appearance of ingested CHO.     

Plasma metabolites, volume and electrolytes following 30-s high-intensity exercise in boys and men

It has been shown that boys recover faster than men following brief, high-intensity exercise. Better to understand this difference, plasma metabolite concenration, volume, electrolyte concentration [electrolyte], and hydrogen ion concentration [H⁺] changes were compared in five prepubescent boys [mean age 9.6 (SD 0.9) years] and 5 men [mean age 24.9 (SD 4.3) years] following 30-s, all-out cycling. Blood was collected prior to, at the end, and at the 1st, 3rd and 10th min following exercise. At the 10th min of recovery, the men's lactate concentration was 14.2 (SD 1.8) mmol · l^–1 and [H⁺] was 66.1 (SD 5.9) nmol · l^–1, compared with 5.7 (SD 0.7) mmol · l^–1 and 47.5 (SD 1.2) nmol · l^–1 respectively, in the boys (P < 0.01 for both). The glycerol concentration was higher in the boys at the end of exercise and until the 3rd min of recovery. Plasma volume (PV) decreased more in the men [16.9 (SD 3.0)%] than in the boys [9.4 (SD 2.8)%]. In both groups, [electrolyte] increased after exercise, tending to be higher in the men. Recovery of plasma [electrolyte] and PV started earlier in the boys (1st min) than in the men (3rd min). These findings would support the notion of a lesser reliance on glycolytic energy pathways in children and may explain the faster recovery of muscle power in boys compared to men.     

Perceived exertion and blood lactate concentration during graded treadmill running

The purpose of this study was to investigate the influences of treadmill gradients on the rating of perceived exertion (RPE) at two fixed blood lactate concentrations ( [La^–]_b). Ten subjects performed three different incremental treadmill protocols by running either uphill (concentrically-biased), downhill (eccentrically-biased), or on the flat (non-biased). Individual data of each protocol were interpolated to reflect [La^–]_b corresponding to 2.0 and 4.0 mmol·l^–1. At 2.0 mmol·l^–1 [La^– _b, RPE and treadmill speed during downhill running were greater than during level running which was greater than during uphill running (p < 0.05) . Also, the downhill heart rate (HR) was greater than the uphill HR, and downhill minute ventilation ( ) was greater than the level . Treadmill speed was the only measure at 4.0 mmol·l^–1 [La^–]_b to differ between gradients. There was a moderate correlation of RPE with HR at both [La^–]_b (r = 0.73 at 2.0 mmol·l^–1;r = 0.48 at 4.0 mmol·l^–1) while treadmill speed was moderately correlated with RPE only at 2.0 mmol·l^–1 [La^–]_b (r = 0.70). The results of this study demonstrated that the degree of eccentric-bias during running exercise is an influence of perceived exertion at a moderate but not at a high exercise intensity.     

The hormonal responses to repetitive brief maximal exercise in humans

Summary The responses of nine men and nine women to brief repetitive maximal exercise have been studied. The exercise involved a 6-s sprint on a non-motorised treadmill repeated 10 times with 30 s recovery between each sprint. The total work done during the ten sprints was 37,693±3,956 J by the men and 26,555±4,589 J by the women (M > F,P<0.01). This difference in performance was not associated with higher blood lactate concentrations in the men (13.96± 1.70 mmol·^–1) than the women (13.09±3.04 mmol·l^–1). An 18-fold increase in plasma adrenaline (AD) occurred with the peak concentration observed after five sprints. The peak AD concentration in the men was larger than that seen in the women (9.2 +- 7.3 and 3.7 ± 2.4 nmol · l^–1 respectively,P<0.05). The maximum noradrenaline (NA) concentration occurred after ten sprints in the men (31.6±10.9 nmol·l^–1) and after five sprints in the women (27.4 ± 20.8 nmol · l^–1). Plasma cardiodilatin (CDN) and atrial natriuretic peptide (ANP) concentrations were elevated in response to the exercise. The peak ANP concentration occurred immediately postexercise and the response of the women (10.8 ± 4.5 pmol · l^–1 was greater than that of the men (5.1 ± 2.6 pmol · l^–1,P<0.05). The peak CDN concentrations were 163 ± 61 pmol · l^–1 for the women and 135 ± 61 pmol · l^–1 for the men. No increases in calcitonin gene related peptide (CGRP) were detected in response to the exercise. These results indicate differences between men and women in performance and hormonal responses. There was no evidence for a role of CGRP in the control of the cardiovascular system after brief intermittent maximal exercise.     

Maximal oxygen uptake and erythropoietic responses after training at moderate altitude

Summary Six well-trained male cross-country skiers trained for 7 days at 2700 m above sea level, their accommodation being at 1695 m. Blood samples for haemoglobin concentration [Hb], erythropoietin concentration [EPO] and reticulocyte count were collected before, during and after altitude exposure. Packed cell volume (PCV), red blood cell count (RBC), transferrin-iron saturation, mean red cell volume (MCV), mean corpuscular haemoglobin concentration (MCHC), maximal oxygen uptake, maximal achieved ventilation and heart rate were determined pre- and postaltitude exposure. The [EPO] increased significantly from prealtitude (mean 36 mU·ml^–1, SD 5) to maximal altitude values (mean 47 mU·ml^–1, SD 3). The [Hb] had increased significantly above pre-altitude values (mean 8.8 mmol·l^–1, SD 0.5) on day 2 (mean 9.1 mmol·l^–1, SD 0.4) and day 7 (mean 9.4 mmol·l^–1, SD 0.4) at altitude and on day 4 postaltitude (mean 9.2 mmol·l^–1, SD 0.4). The reticulocyte counts had increased significantly above pre-altitude values (mean 6, SD 3) on day 3 at altitude (mean 12, SD 8) and day 4 postaltitude (mean 10, SD 5). The RBC counts had increased on the 4th postaltitude day. The transferrin-iron saturation had decreased below pre-altitude values (mean 23%, SD 4%) on day 4 postaltitude (mean 14%, SD 5%) and had increased on day 11 postaltitude (mean 22%, SD 7%). There were no significant changes in MCV, MCHC, PCV, maximal oxygen uptake and maximal achieved ventilation, and heart rate pre- to postaltitude. These observations demonstrated an erythropoietic response to the altitude training which was not sufficient to increase the postaltitude maximal oxygen uptake.     

The acute effect of 30 min of moderate exercise on high density lipoprotein cholesterol in untrained middle-aged men

Summary Fifteen middle-aged, untrained (defined as no regular exercise) men (mean age 49.9 years, range 42–67) cycled on a cycle ergometer at 50 rpm for 30 min at an intensity producing 60% predicted maximum heart rate [(f _c,max), wheref _{c, max} = 220 - age]. Total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C) and triglyceride (Tg) concentrations were measured from fasting fingertip capillary blood samples collected at rest, after 15 and 30 min of exercise, and at 15 min post-exercise. The mean HDL-C level increased significantly from the resting level of 0.85 mmol · l^–1 to 0.97 mmol · 1^–1 (P<0.05) after 15 min of exercise, increased further to 1.08 mmol · 1^–1 (P<0.01) after 30 min of exercise and remained elevated at 1.07 mmol · 1^–1 (P<0.01) at 15 min post-exercise. These increases represented changes above the mean resting level of 14.1%, 27.1% and 25.9% respectively. The HDL-C/LDL-C ratio increased significantly from a resting ratio of 0.20 to 0.26 after 30 min of exercise (P < 0.01) and to 0.24 at 15 min post-exercise (P<0.05). The mean Tg level increased significantly from a resting level of 0.88 mmol · 1^–1 to 1.05 mmol · 1^–1 after 15 min, and to 1.06 mmol · I^–1 after 30 min of exercise (P<0.05 at each time). The TC/HDL-C ratio decreased significantly (P=0.05) after 30 min of exercise and at 15 min post-exercise by 18.8% and 14%, respectively. No significant changes were observed in the levels of TC or LDL-C over time. These results indicate that 30 min of moderate exercise elicits significant changes in HDL-C concentration during and up to 15 min after the exercise in untrained middle-aged men with low mean resting levels of HDL-C (0.85 mmol · 1^–1).     

Effects of exercise during normoxia and hypoxia on the growth hormone—insulin-like growth factor I axis

The response of plasma insulin-like growth factor I (IGF I) to exercise-induced increase of total human growth hormone concentration [hGH_tot] and of its molecular species [hGH_20kD] was investigated up to 48 h after an 1-h ergometer exercise at 60% of maximal capacity during normoxia (N) and hypoxia (H) (inspiratory partial pressure of oxygen = 92 mmHg (12.7 kPa);n = 8). Lactate and glucose concentrations were differently affected during both conditions showing higher levels under H. Despite similar maximal concentrations, the increase of human growth hormone (hGH) was faster during exercise during H than during N[hGH_tot after 30 min: 8.6 (SD 11.4) ng · ml^–1 (N); 16.2 (SD 11.6) ng · ml^–1 (H);P < 0.05]. The variations in plasma [hGH_20kD] were closely correlated to those of [hGH_tot], but its absolute concentration did not exceed 3% of the [hGH_tot]. Plasma IGF I concentration was significantly decreased 24 h after both experimental conditions [N from 319 (SD 71) ng · ml^-1 to 228 (SD 72) ng · ml^–1,P < 0.05; H from 253 (SD 47) to 200 (SD 47) ng · ml^–1,P < 0.01], and was still lower than basal levels 48 h after exercise during H [204 (SD 44) ng · ml^–1,P < 0.01]. Linear regression analysis yielded no significant correlation between increase in plasma [hGH_tot] or [hGH_20kD] during exercise and the plasma IGF I concentration after exercise. It was concluded that the exercise-associated elevated plasma [hGH] did not increase the hepatic IGF I production. From our study it would seem that the high energy demand during and after the long-lasting intensive exercise may have overridden an existing hGH stimulus on plasma IGH I, which was most obvious during hypoxia.     

The influence of a 1-year programme of brisk walking on endurance fitness and body composition in previously sedentary men aged 42–59 years

This study examined the influence of a 1-year brisk walking programme on endurance fitness and the amount and distribution of body fat in a group of formerly sedentary men. Seventy-two males, aged 42–59 years, body mass index 25.2 (0.3) kg·m^–2 [mean (SEM)], were randomly allocated to either a walking group (n = 48) or control group (n = 24). Brisk walking speed was evaluated using a 1.6-km track walk. Changes in endurance fitness were assessed by measuring blood lactate concentration and heart rate during submaximal treadmill walking. Body composition was determined by hydrostatic weighing and anthropometry; energy intake was assessed from 7-day weighed food inventories. Differences in the response of walkers and controls were examined using two-way analyses of variance. Forty-two walkers (87.5%) completed the study and averaged 27.9 (1.4) min·day^–1 of brisk walking (range 11–46). Brisk walking speed averaged 1.95 (0.03) m·s^–1 and elicited approximately 68 (1) % of maximum heart rate. Heart rate and blood lactate concentration during submaximal treadmill walking were significantly reduced in the walkers after 3, 6 and 12 months and the oxygen uptake at a reference blood lactate concentration of 2 mmol·l^–1 was increased by 3.2 ml·kg^–1. min^–1 (14.9%) in the walkers at 6 months (P< 0.01). Although skinfold thicknesses at anterior thigh and medial calf sites decreased significantly for the walkers, the response of the two groups did not differ significantly for other body composition variables or for energy intake.     

Post-exercise rehydration in man: effects of electrolyte addition to ingested fluids

This study examined the effects on water balance of adding electrolytes to fluids ingested after exercise-induced dehydration. Eight healthy male volunteers were dehydrated by approximately 2% of body mass by intermittent cycle exercise. Over a 30-min period after exercise, subjects ingested one of the four test drinks of a volume equivalent to their body mass loss. Drink A was a 90 mmol·l^–1 glucose solution; drink B contained 60 mmol·l^–1 sodium chloride; drink C contained 25 mmol·l^–1 potassium chloride; drink D contained 90 mmol·l^–1 glucose, 60 mmol·l^–1 sodium chloride and 25 mmol·l^–1 potassium chloride. Treatment order was randomised. Blood and urine samples were obtained at intervals throughout the study; subjects remained fasted throughout. Plasma volume increased to the same extent after the rehydration period on all treatments. Serum electrolyte (Na⁺, K⁺ and Cl^–) concentrations fell initially after rehydration before returning to their pre-exercise levels. Cumulative urine output was greater after ingestion of drink A than after ingestion of any of the other drinks. On the morning following the trial, subjects were in greater net negative fluid balance [mean (SEM);P<0.02] on trial A [745 (130) ml] than on trials B [405 (51) ml], C [467 (87) ml] or D [407 (34) ml]. There were no differences at any time between the three electrolyte-containing solutions in urine output or net fluid balance. One hour after the end of the rehydration period, urine osmolality had fallen, with a significant treatment effect (P=0.016); urine osmolality was lowest after ingestion of drink A. On the morning after the test, subjects were in greater net negative sodium balance (P<0.001) after trials A and C than after trials B and D. Negative potassium balance was greater (P<0.001) after trials A and B than after C and D. Chloride balance was positive after drink D and a smaller negative balance (P<0.001) was observed after drink B than after A and C. These results suggest that although the measured blood parameters were similar for all trials, better whole body water and electrolyte balance resulted from the ingestion of electrolyte-containing drinks. There appeared, however, to be no additive effect of including both sodium and potassium under the conditions of this experiment.     

The physical demands of riding in National Hunt races

Heart rate (f _c) and post-competition blood lactate concentration ([La⁺]) were studied in seven male professional National Hunt jockeys over 30 races. Thef _c response for individual races followed a similar pattern for all subjects. The mean peakf _c recorded during competition was 184 beats·min^–1 (range 162–198 beats·min^–1) with averagef _c during the races ranging from 136 to 188 beats·min^–1. During consecutive races the recoveryf _c did not return to resting values. The mean [La⁺] was 7.1 mmol·l^–1 (range 3.5–15.0 mmol·l^–1). The conclusions of this study suggest that riding in National Hunt races is a physically demanding occupation. The muscular activity in this profession requires a high metabolic drive and produces a significant cardiorespiratory response.     

Exercise induces pentane production and neutrophil activation in humans. Effect of propranolol

Summary The effect of -adrenergic receptor blockade on exercise-induced lipid peroxidation in man has been examined by measuring the production of pentane in expired air. For this purpose, five healthy male subjects were subjected to dynamic exercise of graded intensity on a cycle ergometer (10 min at 45%, 5 min at 60% and 75% maximal oxygen uptake 1 h after ingestion of either a placebo or 40-mg propranolol. At rest, mean pentane concentration ([pent]) with placebo was 4.13 pmol · l^–1, SD 2.14. After exercise, this value significantly increased by 310% (17.1 pmol · l^–1, SD 7.73, P < 0.01). Oral administration of 40-mg propranolol significantly lowered the mean resting [pent] to 1.75 pmol · l^–1, SD 0.77, P < 0.05. After exercise, the increase of [pent] was much smaller (240%) and was less significant (P < 0.2) than with the placebo. The mechanism of this inhibitory effect of propranolol remains to be elucidated. However, as indicated by the measurement of plasma myeloperoxidase concentration, it can be concluded that the antioxidant property of propranolol cannot be attributed to the inhibition of neutrophil activation, a possible source of free radicals during exercise.     

Physiological changes and gastro-intestinal symptoms as a result of ultra-endurance running

Summary One hundred and seventy-two competitors of the Swiss Alpine Marathon, Davos, Switzerland, 1988, volunteered for this research project. of these volunteers 170 (158 men, 12 women) finished the race (99%). The race length was 67 km with an altitude difference of 1,900 m between the highest and lowest points. Mean age was 39 (SEM 0.8) years. Average finishing times were 8 h 18 min (men) and 8 h 56 min (women). Loss of body mass averaged 3.4% body mass [mean 3.3 (SEM 0.2)%; 4.0 (SEM 0.4)%; men and women, respectively]. Blood samples from a subgroup of 89 subjects (6 women and 83 men) were taken prior to and immediately after completion of the race. Changes in haemoglobin (9.3 mmol·l^–1 pre-race, 9.7 mmol·l^–1 post-race) and packed cell volume (0.44 pre, 0.48 post-race) were in line with the moderate level of dehydration displayed by changes in body mass. Mean plasma volume decreased by 8.3%. No significant changes in plasma osmolality, sodium, or chloride were observed but plasma potassium did increase by 5% (4.2 mmol·l^–1 pre-race, 4.4 mmol·l^–1 post-race). Mean fluid consumption was 3290 (SEM 103) ml. Forty-three percent of all subjects, and 33% of those who gave blood samples, complained of gastro-intestinal (GI) distress during the race. No direct relationship was found between the quantity or quality of beverage consumed and the prevalence of GI symptoms. The circulating concentration of several GI hormones was measured and several were found to be significantly elevated (P<0.05) after the race [mean values: gastrin 159.6 (SEM 17.8) ng·l^–1; vaso-active intestinal peptide 224.3 (SEM 20.1) ng·l^–1; peptide histidine isoleucine 311.1 (SEM 27.5) ng·l^–1 ; motilin 214.1 (SEM 15.1) ng·l^–1] but larger increases were not found to be significantly correlated with GI symptoms. Plasma cortisol, adrenaline, and noradrenaline concentrations were significantly higher after the race compared to resting values (P<0.05). There was a trend for post-race noradrenaline values to be lower in sufferers of GI disturbance. The post-race plasma noradrenaline concentration was significantly lower specifically in those runners with intestinal cramps. Also, the resting plasma cortisol concentration was significantly lower in those individuals who developed intestinal cramps during the race. Plasma creatine phosphokinase, alanine aminotransferase and aspartate aminotransferase activities were increased following the race, which may indicate that there was tissue damage. An increase in plasma potassium concentration was observed after the race in individuals with GI complaints [0.29 (SEM 0.07) mmol·l^–1 increase], whereas no increase was observed in individuals without GI symptoms. An inability of the Na⁺-K⁺ pump to keep pace with the needs of skeletal muscle (as well in the intestinal tract) may have accounted for the high plasma potassium values immediately following exercise and may have played a role in the development of GI disorders. However, many other sources of K⁺ release may have accounted for the elevated plasma K⁺ (skeletal muscle, liver and red blood cells) in such sufferers and the correlation between the increase in K⁺ and GI symptoms may be an indirect one.     

Pathways of phosphate transport in chick jejunum

The effect of vitamin D₃ on intestinal phosphate (P_i) absorption was studied in everted sacs prepared from jejunum of either vitamin D-deficient (–D) or vitamin D-replete (+D) chicks. Vitamin D₃ stimulates the maximal velocity (V _max) of a mucosal active P_i transport mechanism from 125 to 314 nmol·min^–1·g^–1 tissue.K _m of this process remains virtually unchanged (–D: 0.15 mmol·l^–1; + D: 0.18 mmol·l^–1).Active P_i entry into the epithelium depends on extracellular Na⁺. Reduction of buffer Na⁺ reducesV _max in the + D group to 182 nmol·min^–1·g^–1 tissue but has no significant effect in the –D animals (V _max=105 nmol·min^–1·g^–1 tissue). In this group, the predominant effect of Na⁺ substitution is a shift ofK _m to 1.13 mmol·l^–1, whileK _m in the +D group is changed only to 0.53 mmol·l^–1.Transeptithelial P_i transport in the + D group involves the mucosal phosphate pump and hence an intracellular pathway, proceeding at a rate of 48 nmol·min^–1·g^–1 tissue. This is in contrast to –D P_i transfer (8 nmol·l^–1·g^–1 tissue) which is by a diffusional, Na⁺-insensitive, and presumably paracellular pathway.Transepithelial calcium transport (–D: 3.3 nmol·min^–1·g^–1; + D: 7.6 nmol·min^–1·g^–1 tissue) does not require the presence of extracellular Na⁺ and apparently involves pathways different from those of the P_i absorptive system.Presented in part at the Annual Meeting of the Austrian Biochemical Society, Salzburg, September 1978     

Arterial diameter during central volume depletion in humans

The luminal diameter of the radial artery was followed by high frequency ultrasound during 50° head-up tilt-induced central volume depletion in ten healthy subjects of whom six were tilted twice and pretreated with the serotonin receptor antagonist methysergide or placebo following a double-blind randomized design. Eight subjects without active treatment experienced presyncopal symptoms after 16–45 (mean 32 min). Central volume depletion was indicated by an increase in mean thoracic electrical impedance [from 31.5 (SEM 1.6) to 33.4 (SEM 1.7) P < 0.05]. Cardiac output decreased [from 4.1 (SEM 0.3) to 2.2 (SEM 0.3) l · min^–1] and heart rate [HR, from 64 (SEM 3) to 100 (SEM 7) beats · min^–1], mean arterial pressure {MAP, from 77 (SEM 4) to 89 (SEM 2) mmHg [10.3 (SEM 0.53 to 11.9 (SEM 0.27) kPa]} and total peripheral resistance {TPR, from 19 (SEM 2) to 34 (SEM 4) mmHg · min · l^–] [2.5 (SEM 0.27) to 4.5 (SEM 0.53) kPa · min^–1]} increased; but with the appearance of presyncopal symptoms, HR, MAP and TPR were reduced to 65 (SEM 8) beats · min^–1, 46 (SEM 4) mmHg [6.1(SEM 0.53) kPa] and 18 (SEM 3) mmHg · min · l^–1 [2.4 (SEM 0.4) kPa · min^–1 · l^–], respectively (P < 0.05). Vascular resistance was reflected in the arterial diameter which decreased from 2.42 (SEM 0.17) to 2.27 (SEM 0.14) mm during head-up tilt and increased to 2.71 (SEM 0.14) mm with the appearance of presyncopal symptoms (P < 0.05). Methysergide reduced the resting radial (15 ± 2%) and temporal artery diameters (10 ± 3%) (P < 0.05); however, it affected neither tilt-tolerance nor the central cardiovascular response to tilt. The results suggested a serotonergic influence on arterial tone at rest, and demonstrated that vessels as large as the radial artery participated in vascular control during central volume depletion independent of such a serotonergic influence.     

Effects of protein supplementation during prolonged exercise at moderate altitude on performance and plasma amino acid pattern

Summary The effects of two levels of protein intake on muscle performance and energy metabolism were studied in humans submitted to repeated daily sessions of prolonged exercise at moderate altitude. For this purpose, 29 healthy males, were exposed to seven successive stages of ski-mountaineering at altitudes between 2500 and 3 800 m, and to an isocaloric diet (4000 kcal·day^–1, 16760 kJ·day^–1) with either 1.5g·kg^–1·day^–1 (C group,n =14), or 2.5 g·kg^–1·day^–1 (PR group,n =15) protein intake. Measurements made after the ski-mountaineering programme did not show any change in body mass. The peak torque during maximal isometric voluntary contraction (MVC) of the quadriceps muscle was unaffected by the repeated exercises, whereas the endurance time at 50% MVC was decreased in PR subjects (–26.8%,P<0.001). Increased levels of both free fatty acids (+147%,P<0.001) and glycerol (+170%,P<0.001) observed in C subjects would suggest that lipolysis was enhanced after the repeated exercise. The plasma amino acid pattern was altered after completion of the ski-mountaineering programme; the plasma concentration of the three branched-chain amino acids (BCAA) was significantly decreased in C subjects, whereas the higher level of protein intake (PR group) greatly minimized the exercise-induced decrease in serum BCAA.     

Electrophysiological effects of acetylcholine in sheep cardiac Purkinje fibers

The addition of acetylcholine (ACh) in concentrations of 10^–7 to 10^–5 mol·l^–1 to normal Tyrode solution results in the following changes of the electrical activity in sheep cardiac Purkinje fibers: prolongation of the action potential and shift of the plateau to more positive values, hyperpolarization of the maximum diastolic potential (E _max), and increase of the rate of diastolic depolarization.Prolongation of the action potential and shift of the plateau in the positive direction were more pronounced in distal Purkinje fibers, at low frequencies of stimulation, and in the presence of a reduced Ca (<3.6 mmol·l^–1) or K extracellular concentration (<5.4 mmol·l^–1); the effects persisted in Cl free media or after addition of Mn (2–10 mmol·l^–1) or verapamil (1–5 mg·l^–1).The effect of Ach on the maximum diastolic potential (stimulation frequency 60/min) was dependent on K₀. At 5.4 mmol·l^–1,E _max increased by 2 mV; at higher K₀ concentrations the change was less pronounced or absent; at low K₀ concentrations (membrane potential arrested at the plateau level) the addition of Ach invariably caused a depolarization. In unstimulated preparations the effect of Ach was unpredictable.The increase in rate of diastolic depolarization by Ach in 3.4 or 2.7 mmol·l^–1 K was large enough to result in spontaneous activity. When the membrane was depolarized to the plateau level (K₀<1.35 mmol·l^–1) Ach frequently reduced the frequency of oscillations.The effect of Ach was dose-dependent; desensitization was absent. Similar results were obtained with carbachol (10^–6 mol·l^–1) or choline (5·10^–3 mol·l^–1). The effect of Ach could selectively be abolished by atropine (10^–8 to 10^–6 mol·l^–1); it was not modified by succinylcholine (8·10^–5 mol·l^–1), phentolamine (10^–6 mol·l^–1) or propranolol (10^–6 mol·l^–1). The results indicate that the electrophysiological changes are due to stimulation of muscarinic receptors.Except for the hyperpolarization ofE _max the results in sheep Purkinje fibers are different and even opposite to those observed in the sino-atrial node and atrial muscle. Possible mechanisms and functional significance of the results are discussed.Supported by F.G.W.O. Belgium 3.0087.74     

Relationships between postcompetition blood lactate concentration and average running velocity over 100-m and 200-m races

The relationships between anaerobic glycolysis and average velocity () sustained during sprint running were studied in 12 national level male sprinters. A blood sample was obtained within 3 min of the completion of semi-finals and finals in the 100-m and 200-m Cameroon national championships and blood lactate concentration ([la^–]_b) was measured. The 35-m times were video-recorded. The 100-m and 200-m [la^–]_b were 8.5 (SD 0.8) and 10.3 (SD 0.8) mmol·l^–1, respectively. These were not correlated with the performances. Over 200 m [la^–]_b was correlated with the sustained over the last 165 m (r=0.65,P<0.05). In the 9 athletes who participated in both the 100-m and 200-m races, the difference between the [la^–]_b measured at the end of the two races was negatively correlated to the difference in v sustained over the two races (r=0.76,P>0.02). Energy expenditure during sprint running was estimated from the [la^–]_b values. This estimate was mainly based on the assumption that a 1 mmol·l^–1 increase in [la^–]_b corresponds to the energy produced by the utilization of 3.30 ml O₂·kg^–1. The energy cost of running was estimated at 0.275 (SD 0.02) ml O₂·kg^–1·m^–1 over 200-m and 0.433 (SD 0.03) ml O₂·kg^–1·m^–1 over 100-m races. These results would suggest that at the velocities studied anaerobic glycolysis contributes to at least 55% of the energy expenditure related to sprint running. However, the influence of both mechanical factors and the contribution of other energy processes obscure the relationship between [la^–]_b and performance.