Influence of body temperature on the development of fatigue during prolonged exercise in the heat

We investigated whether fatigue during prolonged exercise in uncompensable hot environments occurred at the same critical level of hyperthermia when the initial value and the rate of increase in body temperature are altered. To examine the effect of initial body temperature [esophageal temperature (Tes) = 35.9 +/- 0.2, 37.4 +/- 0. 1, or 38.2 +/- 0.1 (SE) degrees C induced by 30 min of water immersion], seven cyclists (maximal O2 uptake = 5.1 +/- 0.1 l/min) performed three randomly assigned bouts of cycle ergometer exercise (60% maximal O2 uptake) in the heat (40 degrees C) until volitional exhaustion. To determine the influence of rate of heat storage (0.10 vs. 0.05 degrees C/min induced by a water-perfused jacket), four cyclists performed two additional exercise bouts, starting with Tes of 37.0 degrees C. Despite different initial temperatures, all subjects fatigued at an identical level of hyperthermia (Tes = 40. 1-40.2 degrees C, muscle temperature = 40.7-40.9 degrees C, skin temperature = 37.0-37.2 degrees C) and cardiovascular strain (heart rate = 196-198 beats/min, cardiac output = 19.9-20.8 l/min). Time to exhaustion was inversely related to the initial body temperature: 63 +/- 3, 46 +/- 3, and 28 +/- 2 min with initial Tes of approximately 36, 37, and 38 degrees C, respectively (all P < 0.05). Similarly, with different rates of heat storage, all subjects reached exhaustion at similar Tes and muscle temperature (40.1-40.3 and 40. 7-40.9 degrees C, respectively), but with significantly different skin temperature (38.4 +/- 0.4 vs. 35.6 +/- 0.2 degrees C during high vs. low rate of heat storage, respectively, P < 0.05). Time to exhaustion was significantly shorter at the high than at the lower rate of heat storage (31 +/- 4 vs. 56 +/- 11 min, respectively, P < 0.05). Increases in heart rate and reductions in stroke volume paralleled the rise in core temperature (36-40 degrees C), with skin blood flow plateauing at Tes of approximately 38 degrees C. These results demonstrate that high internal body temperature per se causes fatigue in trained subjects during prolonged exercise in uncompensable hot environments. Furthermore, time to exhaustion in hot environments is inversely related to the initial temperature and directly related to the rate of heat storage.

Human circulatory and thermoregulatory adaptations with heat acclimation and exercise in a hot, dry environment

1. Heat acclimation was induced in eight subjects by asking them to exercise until exhaustion at 60% of maximum oxygen consumption rate (VO2) for 9-12 consecutive days at an ambient temperature of 40 degrees C, with 10% relative humidity (RH). Five control subjects exercised similarly in a cool environment, 20 degrees C, for 90 min for 9-12 days; of these, three were exposed to exercise at 40 degrees C on the first and last day. 2. Acclimation had occurred as seen by the increased average endurance from 48 min to 80 min, the lower rate of rise in the heart rate (HR) and core temperature and the increased sweating. 3. Cardiac output increased significantly from the first to the final heat exposure from 19.6 to 21.4 l min-1; this was possibly due to an increased plasma volume and stroke volume. 4. The mechanism for the increased plasma volume may be an isosmotic volume expansion caused by influx of protein to the vascular compartment, and a sodium retention induced by a significant increase in aldosterone. 5. The exhaustion coincided with, or was elicited when, core temperature reached 39.7 +/- 0.15 degrees C; with progressing acclimation processes it took progressively longer to reach this level. However, at this point we found no reduction in cardiac output, muscle (leg) blood flow, no changes in substrate utilization or availability, and no recognized accumulated 'fatigue' substances. 6. It is concluded that the high core temperature per se, and not circulatory failure, is the critical factor for the exhaustion during exercise in heat stress.

Hyperthermia and central fatigue during prolonged exercise in humans

The present study investigated the effects of hyperthermia on the contributions of central and peripheral factors to the development of neuromuscular fatigue. Fourteen men exercised at 60% maximal oxygen consumption on a cycle ergometer in hot (40 degrees C; hyperthermia) and thermoneutral (18 degrees C; control) environments. In hyperthermia, the core temperature increased throughout the exercise period and reached a peak value of 40.0 +/- 0.1 degrees C (mean +/- SE) at exhaustion after 50 +/- 3 min of exercise. In control, core temperature stabilized at approximately 38.0 +/- 0.1 degrees C, and exercise was maintained for 1 h without exhausting the subjects. Immediately after the cycle trials, subjects performed 2 min of sustained maximal voluntary contraction (MVC) either with the exercised legs (knee extension) or with a "nonexercised" muscle group (handgrip). The degree of voluntary activation during sustained maximal knee extensions was assessed by superimposing electrical stimulation (EL) to nervus femoralis. Voluntary knee extensor force was similar during the first 5 s of contraction in hyperthermia and control. Thereafter, force declined in both trials, but the reduction in maximal voluntary force was more pronounced in the hyperthermic trial, and, from 30 to 120 s, the force was significantly lower in hyperthermia compared with control. Calculation of the voluntary activation percentage (MVC/MVC + EL) revealed that the degree of central activation was significantly lower in hyperthermia (54 +/- 7%) compared with control (82 +/- 6%). In contrast, total force of the knee extensors (MVC + force from EL) was not different in the two trials. Force development during handgrip contraction followed the same pattern of response as was observed for the knee extensors. In conclusion, these data demonstrate that the ability to generate force during a prolonged MVC is attenuated with hyperthermia, and the impaired performance is associated with a reduction in the voluntary activation percentage.

Prevalence and causes of albuminuria in non-insulin-dependent diabetic patients

A prospective study of the prevalence and causes of persistent albuminuria (greater than 300 mg/24 hr) was conducted in non-insulin-dependent diabetic (NIDDM) patients, age less than 66 years, attending a diabetic clinic during 1987. All eligible patients (N = 370) were asked to collect at least one 24-hour urine sample for albumin analysis. Urine collection was obtained in 224 males and 139 females (98%). Fifty patients (7 women) suffered from persistent albuminuria (13.8%). The prevalence of albuminuria was significantly higher in males (19%) than in females (5%). A kidney biopsy was performed in 35 patients (70%). The kidney biopsies revealed diffuse and/or nodular diabetic glomerulosclerosis in 27 patients (77%), while the remaining eight patients (23%) had a variety of non-diabetic glomerulopathies, such as minimal lesion and mesangioproliferative glomerulonephritis. Diabetic retinopathy was present in 15 of 27 patients (56%) with diabetic glomerulosclerosis, while none of the eight patients with a non-diabetic glomerulopathy had retinopathy. Our cross sectional study has revealed a high prevalence of albuminuria and of non-diabetic glomerulopathy as a cause of this complication in NIDDM patients. Presence of diabetic retinopathy strongly suggests that a diabetic glomerulopathy is the cause of albuminuria. Albuminuric non-insulin-dependent diabetic patients without retinopathy require further evaluation, that is, kidney biopsy.

Effect of alprenolol on mortality among patients with definite or suspected acute myocardial infarction. Preliminary results

A double-blind study of alprenolol versus placebo was done in patients with definite or suspected myocardial infarction to show the effect of the drug on mortality-rate after a year of treatment in patients aged less than or equal to 65 and to study the tolerance of the drug by patients greater than 65 years of age. The dose given was 5--10 mg intravenously, followed by 200 mg twice a day, orally. Patients in whom beta-blockade was contraindicated were excluded. All deaths, side-effects, and dropouts were recorded. Of the 480 patients in the study, 238 patients received alprenolol and 242 placebo. During the year of follow-up 108 patients dropped out from the study. Mortality was not reduced in patients greater than 65 years of age. In those less than or equal to 65 years alprenolol significantly reduced mortality-rate (20% mortality in placebo group vs 9% in treated group). There was also a significant reduction in mortality-rate among those with definite infarction (28% in the placebo vs 15% in the treated group).

Perceived exertion is associated with an altered brain activity during exercise with progressive hyperthermia

The present study tested the hypothesis that perceived exertion during prolonged exercise in hot environments is associated with changes in cerebral electrical activity rather than changes in the electromyogram (EMG) of the exercising muscles. Therefore, electroencephalogram (EEG) in three positions (frontal, central, and occipital cortex), EMG, rating of perceived exertion (RPE), and core temperature were measured in 14 subjects during submaximal exercise in normal (18 degrees C, control) and hot (40 degrees C, hyperthermia) environments. RPE increased from 11 +/- 1 units at 5 min to 20 +/- 0 units at exhaustion (50 +/- 3 min) in the trial with progressive hyperthermia, whereas exercise in the control trial was maintained with a stable core temperature for 1 h without exhausting the subjects. Altered EEG activity was observed in all electrode positions, and stepwise forward-regression analysis identified core temperature and a frequency index of the EEG over the frontal cortex as the best predictors of RPE. In contrast, there were no significant correlations between RPE and any of the measured EMG parameters (median spectral frequency, root mean square, or amplitude), and the EMG parameters were not different in hyperthermia compared with control. Thus hyperthermia does not seem to affect the activation pattern of the muscles. Rather, the linear correlation among core temperature, EEG frequency index, and RPE indicates that alterations in cerebral activity may be associated with the hyperthermia-induced development of fatigue during prolonged exercise in hot environments.

Muscle blood flow is reduced with dehydration during prolonged exercise in humans

1. The present study examined whether the blood flow to exercising muscles becomes reduced when cardiac output and systemic vascular conductance decline with dehydration during prolonged exercise in the heat. A secondary aim was to determine whether the upward drift in oxygen consumption (VO2) during prolonged exercise is confined to the active muscles. 2. Seven euhydrated, endurance-trained cyclists performed two bicycle exercise trials in the heat (35 C; 40-50 % relative humidity; 61 +/- 2 % of maximal VO2), separated by 1 week. During the first trial (dehydration trial, DE), they bicycled until volitional exhaustion (135 +/- 4 min, mean +/- s.e.m.), while developing progressive dehydration and hyperthermia (3.9 +/- 0.3 % body weight loss; 39.7 +/- 0.2 C oesophageal temperature, Toes). In the second trial (control trial), they bicycled for the same period of time while maintaining euhydration by ingesting fluids and stabilizing Toes at 38.2 +/- 0.1 C after 30 min exercise. 3. In both trials, cardiac output, leg blood flow (LBF), vascular conductance and VO2 were similar after 20 min exercise. During the 20 min-exhaustion period of DE, cardiac output, LBF and systemic vascular conductance declined significantly (8-14 %; P < 0.05) yet muscle vascular conductance was unaltered. In contrast, during the same period of control, all these cardiovascular variables tended to increase. After 135 +/- 4 min of DE, the 2.0 +/- 0.6 l min-1 lower blood flow to the exercising legs accounted for approximately two-thirds of the reduction in cardiac output. Blood flow to the skin also declined markedly as forearm blood flow was 39 +/- 8 % (P < 0.05) lower in DE vs. control after 135 +/- 4 min. 4. In both trials, whole body VO2 and leg VO2 increased in parallel and were similar throughout exercise. The reduced leg blood flow in DE was accompanied by an even greater increase in femoral arterial-venous O2 (a-vO2) difference. 5. It is concluded that blood flow to the exercising muscles declines significantly with dehydration, due to a lowering in perfusion pressure and systemic blood flow rather than increased vasoconstriction. Furthermore, the progressive increase in oxygen consumption during exercise is confined to the exercising skeletal muscles.

Middle cerebral artery blood velocity is reduced with hyperthermia during prolonged exercise in humans

1. In the present study we examined the effect of hyperthermia on the middle cerebral artery mean blood velocity (MCA V(mean)) during prolonged exercise. We predicted that the cerebral circulation would be impaired when hyperthermia is present during exercise and assumed that this could be observed as a reduced MCA V(mean). 2. Eight endurance trained men (maximum oxygen uptake (V(O2,max)) 70 +/- 1 ml min(-1) kg(-1) (mean +/- S.E.M.)) performed two exercise trials at 57 % of V(O2,max) on a cycle ergometer in a hot (40 degrees C; hyperthermic trial) and in a thermoneutral environment (18 degrees C; control trial). In the hyperthermic trial, the oesophageal temperature increased throughout the exercise period reaching a peak value of 40.0 +/- 0.1 degrees C at exhaustion after 53 +/- 4 min of exercise. In the control trial, exercise was maintained for 1 h without any signs of fatigue and with core temperature stabilised at 37.8 +/- 0.1 degrees C after approximately 15 min of exercise. 3. Concomitant with the development of hyperthermia, MCA V(mean) declined by 26 +/- 3 % from 73 +/- 4 cm s(-1) at the beginning of exercise to 54 +/- 4 cm s(-1) at exhaustion (P < 0.001). In contrast, MCA V(mean) remained unchanged at 70-72 cm s(-1) throughout the 1 h control trial. 4. When individually determined regression lines for MCA V(mean) and arterial carbon dioxide pressure (P(a,CO2)) obtained during preliminary exercise tests were used to account for the differences in P(a,CO2) between the hyperthermic and control trial, it appeared that more than half of the reduction in MCA V(mean) (56 +/- 8 %) was related to a hyperventilation-induced drop in P(a,CO2). Declining cardiac output and arterial blood pressure accounted for the remaining part of the hyperthermia-induced reduction in MCA V(mean). 5. The present results demonstrate that the development of hyperthermia during prolonged exercise is associated with a marked reduction in MCA V(mean).

Brain activity and fatigue during prolonged exercise in the heat

We hypothesized that fatigue due to hyperthermia during prolonged exercise in the heat is in part related to alterations in frontal cortical brain activity. The electroencephalographic activity (EEG) of the frontal cortex of the brain was measured in seven cyclists [maximal O2 uptake (VO2max) 4.8 +/- 0.1 (SE) 1 min-1] cycling at 60% VO2max in a hot (H, 42 degrees C) and a cool (C, 19 degrees C) environment. Fast Fourier transformation of the EEG was used to obtain power spectrum areas in the alpha (8-13 Hz) and beta (13-30 Hz) frequencies. The ratio alpha/beta was calculated as an index of arousal level; an elevated alpha/beta index reflects suppressed arousal. In H, subjects fatigued after 34.4 +/- 1.4 min coinciding with an oesophageal temperature (Toes) of 39.8 +/- 0.1 degrees C, an almost maximal heart rate (HR 192 +/- 3 beats.min-1), a rating of perceived exertion (RPE) of 19.0 +/- 0.8 and significantly elevated alpha/beta index (188 +/- 71% of the value after 2 min of exercise; P < 0.05). In C, subjects cycled for a similar period while Toes was below 38 degrees C, HR and RPE were low, and the alpha/beta index was not significantly elevated (59 +/- 27% of 2 min value; P = NS). Increases in the alpha/beta index were strongly correlated to increases in Toes (r2 = 0.98; P = 0.0001).

Elevations in core and muscle temperature impairs repeated sprint performance

AIM

The present study investigated the effects of hyperthermia on intermittent exercise and repeated sprint performance.

METHODS

Seven men completed 40 min of intermittent cycling comprising of 15 s exercise (306 +/- 22 W) and 15 s rest periods (0 W) followed by 5 x 15 s maximal sprints on a cycle ergometer in normal (approximately 20 degrees C, control) and hot (40 degrees C, hyperthermia) environments.

RESULTS

Completion of the intermittent protocol in the heat elevated core and muscle temperatures (39.5 +/- 0.2 degrees C; 40.2 +/- 0.4 degrees C), heart rate (178 +/- 11 beats min(-1)), rating of perceived exertion (RPE) (18 +/- 1) and noradrenaline (38.9 +/- 13.2 micromol l(-1)) (all P < 0.05). During the first sprint (n = 6), both peak and mean power output were similar across the environmental conditions. However, mean power over the last four sprints declined to a larger extent during hyperthermia compared with the control trial (P < 0.05). Consequently, average mean power output during the five sprints was lower in hyperthermia (558.0 +/- 146.9 W) compared with control (617.5 +/- 122.6 W; P < 0.05). Power output during the repeated sprints was reduced by hyperthermia despite an elevated muscle temperature that should promote sprint performance. Venous plasma potassium concentrations (H; 5.3 +/- 0.8 mmol l(-1) vs. C; 6.3 +/- 1.0 mmol l(-1), P = 0.06) and muscle lactate levels (H; 76.6 +/- 24.3 mmol kg(-1) dry weight vs. C; 108.8 +/- 20.1 mmol kg(-1) dry weight) were lower following the hyperthermic sprints compared to control.

CONCLUSION

Although an elevated muscle temperature is expected to promote sprint performance, power output during the repeated sprints was reduced by hyperthermia. The impaired performance does not seem to relate to the accumulation of recognized metabolic fatigue agents and we, therefore, suggest that it may relate to the influence of high core temperature on the function of the central nervous system.

The serological response to Salmonella serovars typhimurium and infantis in experimentally infected pigs. The time course followed with an indirect anti-LPS ELISA and bacteriological examinations

A total of 43 pigs, inoculated with Salmonella typhimurium (O:1,4,5,12) and un-inoculated controls were followed weekly by blood and faecal samplings for up to 18 weeks post inoculation (p.i.). Three pigs, inoculated with S. infantis (O:6,7) were followed similarly for 9 weeks. All inoculated pigs, except one, were positive for Salmonella by traditional faecal culture on at least one occasion during the first week of infection, whereafter shedding of bacteria rapidly declined to < 10% of the pigs from week 7. All control pigs remained Salmonella negative by culture of faecal samples. When examined serologically in an indirect ELISA using mixed purified LPS from S. typhimurium and S. choleraesuis (O:6,7), all but one S. typhimurium infected pig and all S. infantis infected pigs produced significantly increased optical densities (OD) in the ELISA as compared to the control groups. The maximum anti-LPS response was observed at day 22, when 86% of the S. typhimurium inoculated pigs had seroconverted, while the frequency of seropositive pigs peaked at days 30 (92%) and 37 p.i. (92%). Large variations were found among pigs concerning time of seroconversion (between 6 and 37 days p.i.), maximum OD-level attained (between 8 and 130% of a reference serum) and persistence of reaction. At the time of necropsy, 18 weeks p.i., 67% of the S. typhimurium inoculated pigs were found seropositive, while 100% of the S. infantis inoculated pigs were found seropositive at necropsy, 9 weeks p.i. Salmonella in internal organs were detected at necropsy in 4/22 of the S. typhimurium inoculated pigs with persistent anti-LPS reaction and all 3 S. infantis inoculated pigs but in none of the antibody-negative pigs. The ELISA is therefore suitable for screening for the presence of infection with S. typhimurium or S. infantis on a herd basis. Its suitability for other serotypes of Salmonella will require further testing.

Acute and adaptive responses in humans to exercise in a warm, humid environment

Acute and repeated exposure for 8-13 consecutive days to exercise in humid heat was studied. Twelve fit subjects exercised at 150 W [45% of maximum O2 uptake (V.O2,max)] in ambient conditions of 35 degrees C and 87% relative humidity which resulted in exhaustion after 45 min. Average core temperature reached 39.9 +/- 0.1 degrees C, mean skin temperature (T-sk) was 37.9 +/- 0.1 degrees C and heart rate (HR) 152 +/- 6 beats min-1 at this stage. No effect of the increasing core temperature was seen on cardiac output and leg blood flow (LBF) during acute heat stress. LBF was 5.2 +/- 0.3 l min-1 at 10 min and 5.3 +/- 0.4 l min-1 at exhaustion (n = 6). After acclimation the subjects reached exhaustion after 52 min with a core temperature of 39.9 +/- 0.1 degrees C, T-sk 37.7 +/- 0.2 degrees C, HR 146 +/- 4 beats min-1. Acclimation induced physiological adaptations, as shown by an increased resting plasma volume (3918 +/- 168 to 4256 +/- 270 ml), the lower exercise heart rate at exhaustion, a 26% increase in sweating rate, lower sweat sodium concentration and a 6% reduction in exercise V.O2. Neither in acute exposure nor after acclimation did the rise of core temperature to near 40 degrees C affect metabolism and substrate utilization. The physiological adaptations were similar to those induced by dry heat acclimation. However, in humid heat the effect of acclimation on performance was small due to physical limitations for evaporative heat loss.

Muscle blood flow and muscle metabolism during exercise and heat stress

The effect of heat stress on blood flow and metabolism in an exercising leg was studied in seven subjects walking uphill (12-17%) at 5 km/h on a treadmill for 90 min or until exhaustion. The first 30 min of exercise were performed in a cool environment (18-21 degrees C); then subjects moved to an adjacent room at 40 degrees C and continued to exercise at the same speed and inclination for a further 60 min or to exhaustion, whichever occurred first. The rate of O2 consumption, 2.6 l/min (1.8-3.3) (average from cool and hot conditions), corresponded to 55-77% of their individual maximums. In the cool environment a steady state was reached at 30 min. When the subjects were shifted to the hot room, the core temperature and heart rate started to rise and reached values greater than 39 degrees C and near-maximal values, respectively, at the termination of the exercise. The leg blood flow (thermodilution method), femoral arteriovenous O2 difference, and consequently leg O2 consumption were unchanged in the hot compared with the cool condition. There was no increase in release of lactate and no reduction in glucose and free net fatty acid uptake in the exercising leg in the heat. Furthermore, the rate of glycogen utilization in the gastrocnemius muscle was not elevated in the hot environment. There was a tendency for cardiac output to increase in the heat (mean 15.2 to 18.4 l/min), which may have contributed to the increase in skin circulation, together with a possible further reduction in flow to other vascular beds, because muscle blood flow was not reduced.(ABSTRACT TRUNCATED AT 250 WORDS)

Nation-wide Salmonella enterica surveillance and control in Danish slaughter swine herds

A nation-wide Salmonella enterica surveillance and control programme was initiated in Danish finishing herds over the first quarter of 1995. In Denmark, all swine for slaughter are identifiable by a unique herd code. For each herd code, and depending on the herd's annual kill, random samples ranging from four to more than 60 swine are obtained quarterly at the abattoir. A meat sample from each pig is frozen, and meat juice (harvested after thawing) is examined for specific antibodies against S. enterica using an indirect enzyme-linked immunosorbent assay (ELISA). The ELISA combines several S. enterica O-antigens, and allows detection of antibody response after a variety of different S. enterica serovar infections. Results are transferred to a central database, which each month (based on meat-juice tests obtained in the previous 13 weeks) assigns all herds into three S. enterica infection levels: Level 1, in which the S. enterica prevalence is deemed low and acceptable; Level 2, where there is a moderate prevalence of S. enterica seroreactors (from > 50% in the smallest to > 10% in the largest herds); Level 3, in which S. enterica seroreactor prevalence is clearly unsatisfactory (> 50% for most herd sizes). Irrespective of Salmonella level, all herds receive a monthly update on the current results of the S. enterica test results. If a herd is categorized in Level 2 or 3, it must receive an advisory visit by a practising veterinarian and a local swine extension specialist, and certain management hygiene precautions must be taken. If a herd is categorized in Level 3, the finishers from the herd must additionally be slaughtered under special hygiene precautions. This is supervised by the veterinary authorities. During 1995, 604000 samples were tested for S. enterica, corresponding to 3.0% of the total kill. In December 1995, 15522 herds (representing > 90% of the national production) were categorized into one of the three levels: 14551 herds (93.7%) in Level 1; 610 herds (3.9%) in Level 2; 361 herds (2.3%) in Level 3. The proportion of serologically positive meat-juice samples collected during 1995 ranged from a mean of 2.9% in smaller herds (101-200 swine slaughtered per year) to 6.1% in relatively large herds (more than 5000 swine slaughtered per year).

Metabolic and thermodynamic responses to dehydration-induced reductions in muscle blood flow in exercising humans

1. The present study examined whether reductions in muscle blood flow with exercise-induced dehydration would reduce substrate delivery and metabolite and heat removal to and from active skeletal muscles during prolonged exercise in the heat. A second aim was to examine the effects of dehydration on fuel utilisation across the exercising leg and identify factors related to fatigue. 2. Seven cyclists performed two cycle ergometer exercise trials in the heat (35 C; 61 +/- 2 % of maximal oxygen consumption rate, VO2,max), separated by 1 week. During the first trial (dehydration, DE), they cycled until volitional exhaustion (135 +/- 4 min, mean +/- s.e.m.), while developing progressive DE and hyperthermia (3.9 +/- 0.3 % body weight loss and 39.7 +/- 0.2 C oesophageal temperature, Toes). On the second trial (control), they cycled for the same period of time maintaining euhydration by ingesting fluids and stabilising Toes at 38.2 +/- 0.1 degrees C. 3. After 20 min of exercise in both trials, leg blood flow (LBF) and leg exchange of lactate, glucose, free fatty acids (FFA) and glycerol were similar. During the 20 to 135 +/- 4 min period of exercise, LBF declined significantly in DE but tended to increase in control. Therefore, after 120 and 135 +/- 4 min of DE, LBF was 0.6 +/- 0.2 and 1.0 +/- 0.3 l min-1 lower (P < 0.05), respectively, compared with control. 4. The lower LBF after 2 h in DE did not alter glucose or FFA delivery compared with control. However, DE resulted in lower (P < 0.05) net FFA uptake and higher (P < 0.05) muscle glycogen utilisation (45 %), muscle lactate accumulation (4.6-fold) and net lactate release (52 %), without altering net glycerol release or net glucose uptake. 5. In both trials, the mean convective heat transfer from the exercising legs to the body core ranged from 6.3 +/- 1.7 to 7.2 +/- 1.3 kJ min-1, thereby accounting for 35-40 % of the estimated rate of heat production ( approximately 18 kJ min-1). 6. At exhaustion in DE, blood lactate values were low whereas blood glucose and muscle glycogen levels were still high. Exhaustion coincided with high body temperature ( approximately 40 C). 7. In conclusion, the present results demonstrate that reductions in exercising muscle blood flow with dehydration do not impair either the delivery of glucose and FFA or the removal of lactate during moderately intense prolonged exercise in the heat. However, dehydration during exercise in the heat elevates carbohydrate oxidation and lactate production. A major finding is that more than one-half of the metabolic heat liberated in the contracting leg muscles is dissipated directly to the surrounding environment. The present results indicate that hyperthermia, rather than altered metabolism, is the main factor underlying the early fatigue with dehydration during prolonged exercise in the heat.

Effects of marked hyperthermia with and without dehydration on VO(2) kinetics during intense exercise

This study determined whether marked hyperthermia alone or in combination with dehydration reduces the initial rate of rise in O(2) consumption (VO(2) on-kinetics) and the maximal rate of O(2) uptake (VO(2 max)) during intense cycling exercise. Six endurance-trained male cyclists completed four maximal cycle ergometer exercise tests (402 +/- 4 W) when euhydrated or dehydrated (4% body wt) with normal (starting esophageal temperature, 37.5 +/- 0.2 degrees C; mean skin temperature, approximately 31 degrees C) or elevated (+1 and +6 degrees C, respectively) thermal strain. In the euhydrated and normal condition, subjects reached VO(2 max) (4.7 +/- 0.2 l/min) in 228 +/- 34 s, with a mean response time of 42 +/- 2 s, and fatigued after 353 +/- 39 s. Hyperthermia alone or in combination with dehydration reduced mean response time (17-23%), VO(2 max) (16%), and performance time (51-53%) (all P < 0.01) but did not alter the absolute response time (i.e., the time to reach 63% response in the control trial, 3.2 +/- 0.1 l/min, 42 s). Reduction in VO(2 max) was accompanied by proportional decline in O(2) pulse and significantly elevated maximal heart rate (195 vs. 190 beats/min for hyperthermia vs. normal). Preventing hyperthermia in dehydrated subjects restored VO(2 max) and performance time by 65 and 50%, respectively. These results demonstrate that impaired high-intensity exercise performance with marked skin and internal body hyperthermia alone or in combination with dehydration is not associated with a diminished rate of rise in VO(2) but decreased VO(2 max).

Enhanced cerebral CO2 reactivity during strenuous exercise in man

Light and moderate exercise elevates the regional cerebral blood flow by approximately 20% as determined by ultrasound Doppler sonography (middle cerebral artery mean flow velocity; MCA V(mean)). However, strenuous exercise, especially in the heat, appears to reduce MCA V(mean) more than can be accounted for by the reduction in the arterial CO(2) tension (P(a)CO(2)). This study evaluated whether the apparently large reduction in MCA V(mean) at the end of exhaustive exercise relates to an enhanced cerebrovascular CO(2) reactivity. The CO(2) reactivity was evaluated in six young healthy male subjects by the administration of CO(2) as well as by voluntary hypo- and hyperventilation at rest and during exercise with and without hyperthermia. At rest, P(a)CO(2) was 5.1 +/- 0.2 kPa (mean +/- SEM) and MCA V(mean) 50.7 +/- 3.8 cm s(-1) and the relationship between MCA V(mean) and P(a)CO(2 )was linear (double-log slope 1.1 +/- 0.1). However, the relationship became curvilinear during exercise (slope 1.8 +/- 0.1; P < 0.01 vs. rest) and during exercise with hyperthermia (slope 2.3 +/- 0.3; P < 0.05 vs. control exercise). Accordingly, the cerebral CO(2) reactivity increased from 30.5 +/- 2.7% kPa(-1) at rest to 61.4 +/- 10.1% kPa(-1) during exercise with hyperthermia (P < 0.05). At exhaustion P(a)CO(2) decreased 1.1+/- 0.2 kPa during exercise with hyperthermia, which, with the determined cerebral CO(2) reactivity, accounted for the 28 +/- 10% decrease in MCA V(mean). The results suggest that during exercise changes in cerebral blood flow are dominated by the arterial carbon dioxide tension.

Use of muscle fluid as a source of antibodies for serologic detection of Salmonella infection in slaughter pig herds

Fluid drained from a muscle tissue sample was used as an alternative to serum for the detection of specific anti-Salmonella antibodies in an indirect LPS enzyme-linked immunosorbent assay (ELISA). In the first study, serum and muscle fluid from 3 pigs experimentally infected with Salmonella typhimurium showed parallel dilution-response relationships when ELISA optical density (OD) values were plotted against sample dilution. ELISA results obtained with serum diluted 1:400 corresponded to those from muscle fluid diluted 1:30. In a second study, using the predetermined dilutions of individually paired serum and muscle fluid samples from 103 pigs, a high degree of concordance between the serum ELISA and the muscle fluid ELISA was observed. Limits of agreement between the 2 methods were calculated as -8.9 to 12.3 OD%, which was considered acceptable. The muscle fluid ELISA had specificities of 0.91-1.0 and sensitivities of 0.80-0.89 at various cutoff values as compared with the serum ELISA. Muscle fluid is a useful postmortem alternative to serum when used with an ELISA to detect anti-Salmonella antibodies.

The hemodynamic and prognostic significance of echo-Doppler-proven mitral regurgitation in patients with dilated cardiomyopathy

Data from cardiac catheterization at rest and during exercise in 57 patients with dilated cardiomyopathy (DCM) were analyzed to evaluate the bearing of mitral regurgitation (MR) detected by color Doppler echocardiography (CDE) on prognostically important invasive hemodynamic parameters and survival. The etiology of DCM was coronary artery disease in 21 patients and unproven ('idiopathic') in 36 patients. MR was detected by CDE in 34 patients (60%) with an agreement of 93% compared to left ventriculography. Mean age, etiology of DCM and duration of symptoms were similar in patients with and without MR, while patients with MR were in a higher NYHA class, had lower ejection fraction (LVEF) (25 +/- 13 vs. 35 +/- 17%; p < 0.02), larger left ventricular volumes (356 +/- 138 vs. 268 +/- 61 ml; p < 0.01) and higher left ventricular end-diastolic pressure (LVEDP) (21 +/- 9 vs. 13 +/- 7 mm Hg; p < 0.01). At rest, right-sided pressures were higher in patients with MR compared to patients without MR (pulmonary wedge pressure 20 +/- 9 vs. 10 +/- 3 mm Hg, mean pulmonary arterial pressure 30 +/- 11 vs. 20 +/- 8 mm Hg, mean right atrial pressure 9 +/- 4 vs. 4 +/- 2 mm Hg, all p < 0.001), but no significant differences were found in cardiac index (CI) or stroke index (SI).(ABSTRACT TRUNCATED AT 250 WORDS)

Muscle blood flow is not reduced in humans during moderate exercise and heat stress

The effect of heat stress on circulation in an exercising leg was determined using one-legged knee extension and two-legged bicycle exercise, both seated and upright. Subjects exercised for three successive 25-min periods wearing a water-perfused suit: control [CT, mean skin temperature (Tsk) = 35 degrees C], hot (H, Tsk = 38 degrees C), and cold (C, Tsk = 31 degrees C). During the heating period, esophageal temperature increased to a maximum of 37.91, 39.35, and 39.05 degrees C in the three types of exercise, respectively. There were no significant changes in pulmonary O2 uptake (VO2) throughout the entire exercise period with either one or two legs. Leg blood flow (LBF), measured in the femoral vein of one leg by thermodilution, remained unchanged between CT, H, and C periods. Venous plasma lactate concentration gradually declined over time, and no trend for an increased lactate release during the heating period was found. Similarly, femoral arteriovenous O2 difference and leg VO2 remained unchanged between the three exercise periods. Although cardiac output (acetylene rebreathing) was not significantly higher during H, there was a tendency for an increase of 1 and 2 l/min in one- and two-legged exercise, respectively, which could account for part of the increase in total skin blood flow during heating (gauged by changes in forearm blood flow). Because LBF was not reduced during exercise and heat stress in these experiments, the additional increase in skin blood flow must have been met by redistribution of blood away from vascular beds other than active skeletal muscle.

The endometrial response to sequential and continuous combined oestrogen-progestogen replacement therapy

OBJECTIVES

1. To determine the prevalence of endometrial hyperplasia in postmenopausal women taking standard proprietary regimens of sequential oestrogen/progestogen; 2. to determine the effects of nine months treatment with an oral continuous combined regimen of 2 mg 17beta-oestradiol and 1 mg norethisterone acetate (Kliofem [Kliogest outside the UK]; Novo Nordisk, Denmark) on endometrial histology in postmenopausal women.

DESIGN

An open, prospective study in postmenopausal women.

SETTING

Fifty-four menopause clinics in the UK.

PARTICIPANTS

2028 postmenopausal women: 1312 (Group A) taking sequential oestrogen-progestogen hormone replacement therapy (HRT), and 716 (Group B) not taking HRT, were recruited. In Group A, 388 women took preparations containing 10 days of progestogen, 921 had 12 days, and 3 had 13 days per cycle.

METHODS

Endometrial aspiration biopsies were taken towards the end of a three-month run-in period (Group A) or at study entry (Group B), before administration of the continuous combined HRT regimen. Biopsies were repeated at the end of the nine month treatment period.

MAIN OUTCOME MEASURE

Endometrial histology.

RESULTS

Initial endometrial biopsy data were available for 1106 women in Group A, who by the time of endometrial investigation had been taking HRT for a median duration of 2.56 years (5th to 95th centiles: 0.77 to 8.49 years). Data were available for 661 untreated women, who had no bleeding and had not taken HRT within the last year (Group B). Complex hyperplasia was found in 59 women (5.3%), and atypical hyperplasia in a further eight (0.7%) in Group A. In Group B there were no cases with complex hyperplasia, but one woman showed atypical hyperplasia (0.2%). At the end of the nine months of continuous combined therapy there was no case of hyperplasia among 1196 biopsies (upper 95% confidence limit of risk 0.31%) in women completing the study. Within this Group all of the women with complex hyperplasia arising during previous sequential HRT and who completed the study (n = 38) reverted to normal endometrial patterns. There was no case of endometrial carcinoma during the study.

CONCLUSIONS

Despite taking standard regimens of sequential HRT containing at least 10 days of progestogen, there was a 5.3% prevalence of complex endometrial hyperplasia, and a 0.7% prevalence of atypical hyperplasia. However, continuous combined HRT (Kliofem) containing daily progestogen is not associated with an increased risk of hyperplasia and will convert the endometrium to normal in those with complex hyperplasia arising during previous sequential HRT.

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.

Exercise induces the release of heat shock protein 72 from the human brain in vivo

The present study tested the hypothesis that in response to physical stress the human brain has the capacity to release heat shock protein 72 (Hsp72) in vivo. Therefore, 6 humans (males) cycled for 180 minutes at 60% of their maximal oxygen uptake, and the cerebral Hsp72 response was determined on the basis of the internal jugular venous to arterial difference and global cerebral blood flow. At rest, there was a net balance of Hsp72 across the brain, but after 180 minutes of exercise, we were able to detect the release of Hsp72 from the brain (335 +/- 182 ng/min). However, large individual differences were observed as 3 of the 6 subjects had a marked increase in the release of Hsp72, whereas exercise had little effect on the cerebral Hsp72 balance in the remaining 3 subjects. Given that cerebral blood flow was unchanged during exercise compared with values obtained at rest, it is unlikely that the cerebral Hsp72 release relates to necrosis of specific cells within the brain. These data demonstrate that the human brain is able to release Hsp72 in vivo in response to a physical stressor such as exercise. Further study is required to determine the biological significance of these observations.

Studies on the isolation, structural analysis and tissue localization of fetal antigen 1 and its relation to a human adrenal-specific cDNA, pG2

Fetal antigen 1 was purified from second trimester human amniotic fluid by immunospecific affinity chromatography followed by reversed-phase chromatography. Fetal antigen 1 is a single chain glycoprotein with a M(r) of 32-38 kDa. The amino acid composition revealed a high content of cysteines, prolines and amino acids (aa) with acidic side-chains indicating that fetal antigen 1 is a compactly folded, strongly hydrophilic molecule. The N-terminal amino acid sequence (37 aa) revealed no homology to other known protein sequences, implying that fetal antigen 1 is a 'novel' human protein. When the aa sequence was back-translated into the appropriate degenerate sequence of nucleic acids, fetal antigen 1 could be partially aligned to a 'human adrenal-specific mRNA, pG2'. The indirect immunoperoxidase technique demonstrated fetal antigen 1 in fetal hepatocytes, glandular cells of fetal pancreas and in fetal adrenal cortex, whereas fetal medullary cells were fetal antigen 1 negative. In adult specimens fetal antigen 1 was exclusively found within the beta cells of the islets of Langerhans and in the adrenals with pronounced staining in the cortex. Our observations suggest that fetal antigen 1 is encoded by the mRNA defined by the cDNA clone pG2, but definitive sequencing and expression studies of this mRNA have not been achieved.