Hormonal disturbances of fluid-electrolyte metabolism under altitude exposure in man

Early alterations in fluid, electrolytes, and their regulating hormones were investigated in men exposed to 6,000 m simulated altitude (2 h-ascent, 2 h-sojourn, 2 h-return). Hematocrit and serum protein rose with elevated serum osmolality and reduced urine flow upon arrival at 6,000 m, suggesting decreased plasma volume probably due to hypotonic fluid shift to intracellular spaces. Serum K declined reflecting respiratory alkalosis. The exposure raised plasma antidiuretic hormone (ADH), plasma renin activity (PRA), serum cortisol and aldosterone. Increases both in ADH and aldosterone showed close correlations with that in cortisol, suggesting that ADH may be elevated by hypoxic stress in addition to elevated serum osmolality and decreased plasma volume, and that increased secretion of adrenocorticotropin may be the main cause of increased aldosterone, though PRA involvement cannot be excluded. These rises in ADH and aldosterone may act to retain body water, and the latter may exaggerate alkalosis; thus, these hormonal changes may be related to acute mountain sickness.     

Atrial natriuretic factor during hypoxia and mild exercise

The effect of hypoxia on plasma atrial natriuretic factor (ANF), plasma renin activity (PRA), and plasma aldosterone concentration (PAC) was evaluated during 2 h of treadmill exercise at 2 km/h, 0 grade at sea level. Six male subjects exercised on 2 separate days during normoxia (21% O2) and hypoxia (13.3 +/- 0.3% O2). No significant changes in ANF or PRA occurred during either normoxic or hypoxic exercise. However, PAC fell significantly during normoxic exercise (17.5 +/- 3.6 vs. 12.7 +/- 2.6 ng/dl, p less than 0.05) but not during hypoxic exercise. Serum potassium concentration fell during hypoxic exercise (5.0 +/- 0.1 vs. 4.4 +/- 0.1 mmol/l, p less than 0.05) along with bicarbonate (27.8 +/- 0.7 vs. 25.8 +/- 0.6 mmol/l, p less than 0.01). Between normoxic and hypoxic studies there was a significantly higher heart rate during hypoxic exercise (78 +/- 5 vs. 90 +/- 6 b/min, p less than 0.01). The major conclusion of this study is that hypoxia resulting in arterial oxygen saturations of 81 +/- 0.7% does not affect plasma atrial natriuretic factor levels during mild exercise in normal male subjects.     

Role of hypobaria in fluid balance response to hypoxia

To estimate the separate and combined effects of reduced P(B) and O2 levels on body fluid balance and regulating hormones, measurements were made during reduced PB (altitude, ALT; P(B) = 432 mm Hg, F(I(O2)) = 0.207), reduced inspired O2 concentration (normobaric hypoxia, HYX; P(B) = 614 mm Hg, F(I(O2)) = 0.142), and lowered ambient pressure without hypoxia (normoxic hypobaria HYB; P(B) = 434 mm Hg, F(I(O2)) = 0.296). Nine fit and healthy young men were exposed to these conditions for 10 h in a decompression chamber. Lake Louise AMS scores, urine collections, and blood samples were obtained every 3 h, with recovery measurements 2 h after exposure. AMS was significantly greater during ALT than HYX, as previously reported (J. Appl. Physiol. 81:1908-1910. 1996), because the combination of reduced P(B) and P(O2) over the 10 h favored fluid retention by reducing urine volume, while plasma volume (PV) remained higher than during HYX. At ALT the plasma Na+ fell significantly at 6 h, probably from dilution of extracellular fluid, and antidiuretic hormone (ADH) was highest (p = 0.006 versus HYB). The PV, urine flow, free water clearance, and plasma renin activity (PRA) rose significantly during recovery from ALT as AMS symptoms subsided, suggesting increased intravascular fluid and reduced adrenergic tone. During HYB, the plasma aldosterone (ALDO) and K+ levels were significantly elevated, and PRA was highest and ADH lowest, without fluid retention. During HYX, fluid balance was similar to HYB, but PV and ALDO were significantly lower, and ALDO increased significantly in recovery from HYX. The fluid retention at ALT in AMS-susceptible subjects appears related to a synergistic interaction involving reduced P(B) and ADH and ALDO.     

Plasma cortisol, renin, and aldosterone during an intense heat acclimation program

The physiologic responses to an intense heat acclimation (HA) regimen (treadmill, 41.2 degrees C, 8 days, 56 min exercise/44 min rest) and the effects on stress and fluid balance hormone responses were examined in 13 unacclimated male volunteers. Venous blood samples were collected before (PRE) and after (POST) exercise (days 1, 4, 8) and analyzed for plasma renin activity (PRA), aldosterone (ALD), cortisol (PC), plasma volume shifts (delta PV%), sodium concentration (Na+), and potassium concentration (K+). HA responses (day 1 vs day 8) indicated reduced strain (P less than 0.05): decreased heart rate, rectal temperature, skin temperature, improved defense of PV, and attenuated PC responses. While plasma Na+ demonstrated no change during daily exercise, K+ (P less than 0.01), PC, PRA, and ALD increased (P less than 0.05) more than delta PV%(day 1: -7.1%, day 8: -5.1%) accounted for. Na+ and K+ did not change as a result of HA, and there was no change in fluid balance hormones (e.g., PRA, ALD). It was concluded that this intense heat acclimation regimen reduced physiologic strain by mechanisms other than alterations in fluid balance hormones and offered few physiologic advantages which cannot be gained through conventional heat acclimation techniques (e.g., walking).     

Erythropoietin levels in lowlanders and high-altitude natives at 3450 m

BACKGROUND: This study is aimed to determine whether short or prolonged residency at high altitude (HA) elicits erythropoietin (EPO) secretion effectively in subjects who were able to acclimatize and those who were not able to acclimatize and suffered from acute mountain sickness (AMS) and high altitude pulmonary edema (HAPE). METHODS: Plasma EPO was measured in 16 lowland residents (LLR) at sea level (SL) and during 11 d of their sojourn at an altitude of 3450 m. Identical studies were also conducted in LLR acclimatized to HA (LLR-accl), high altitude natives (HAN) and in patients of AMS and HAPE. RESULTS: In LLR at SL, the mean +/- SD EPO levels were 8.93 +/- 3.75 mU x ml(-1), increased significantly after 8 h (20.0 +/- 11.06) of arrival at HA, peaked by day 1 (27.91 +/- 10.74 mU x ml(-1)), and started declining thereafter. The hemoglobin and hematocrit also increased after 8 h of arrival at HA and the increased levels were maintained during sojourn at high altitude. The EPO levels in LLR-accl were found to be significantly higher than the LLR SL values, but were not significantly different in HAN. The EPO levels in patients of AMS were not significantly different than the LLR values during the initial 2 d after arrival at HA but were found to be increased in patients of HAPE. CONCLUSION: Short or prolonged residency at HA is associated with increased secretion of EPO. The EPO response to hypoxia is not significantly altered in AMS but is markedly enhanced in HAPE, which may be due to exaggerated hypoxemia in these patients.     

Fluid-regulatory hormone responses during cycling exercise in acute hypobaric hypoxia

PURPOSE: This study was designed to describe the responses of fluid-regulating hormones during exercise in acute hypobaric hypoxia and to test the hypothesis that they would be dependent on the relative intensity of exercise rather than the absolute workload. METHODS: Thirteen men cycled for 60 min on four occasions in the same individual hydration status: in normoxia at 55% and 75% of normoxia maximal aerobic power (N55 and N75, respectively), in hypoxia (PB = 594 hPa) at the same absolute workload and at the same relative intensity as N55 (H75 and H55, respectively). VO2, heart rate, and rectal and mean skin temperatures were recorded during exercise. The total water loss was measured by the difference in nude body mass adjusted for metabolic losses. Venous blood samples were drawn before and 15, 30, 45, and 60 min after the beginning of exercise to measure variations in plasma volume, osmolality, and concentrations in arginine vasopressin (AVP), atrial natriuretic factor (ANF), plasma renin activity (ARP), aldosterone (Aldo), and noradrenaline (NA). RESULTS: During N55 and H55, AVP, Aldo and ARP did not change, whereas ANF increased slightly. Increases in AVP, Aldo, ARP, and NA were greater during N75 than during H75, whereas the increase in ANF was greater during H75 than N75. CONCLUSION: Plasma levels of AVP, Aldo, and ARP increase during exercise when a threshold is reached and thereafter are dependent on the absolute workload, without any specific effect of hypoxia. The time course of ANF appears to be different from that of the other hormones.     

Hormonal changes after supine posture, immersion, and swimming

This study was undertaken to evaluate the effects of the supine posture, immersion, and swimming on hormones involved in the regulation of hydrosaline equilibrium. Plasma levels of atrial natriuretic peptide (ANP), arginine vasopressin (AVP), plasma renin activity (PRA), and aldosterone (ALDO) were measured by radioimmunoassay in eight untrained young subjects (five males and three females). Blood samples were collected on different days: control morning samples in a relaxed standing posture before each test; after 20 min in a supine position; after 20 min of horizontal immersion in water at 28 degrees C; after 20 min of backstroke swimming (speed about 1 m/s). No changes occurred in AVP levels after each test. ALDO and PRA increased significantly only after swimming and were directly correlated. ANP increased significantly after immersion, but no further increase was observed after swimming. The hematocrit, which increased after swimming, was inversely correlated with ANP levels in the post-exercise samples. These data show that while ALDO and PRA increase only in response to swimming, even at moderate intensity, ANP probably requires more prolonged and intense exercise to reach a significantly higher level than in immersion.     

Attenuated ANF response to exercise in athletes with exercise-induced hypoxemia

Some highly trained endurance athletes develop an exercise-induced hypoxemia (EIH) at least partially due to a hemodynamic factor with a potential stress failure on pulmonary capillaries. Atrial natriuretic factor (ANF) is a pulmonary vasodilatator and its release during exercise could be reduced with endurance training. We hypothesized that athletes exhibiting EIH, who have a greater training volume than non-EIH athletes, have a reduced ANF release during exercise explaining the pathophysiology of EIH. Ten highly trained EIH-athletes (HT-EIH), ten without EIH (HT-nEIH), and nine untrained (UT) males performed incremental exercise to exhaustion. No between group differences occurred in resting ANF plasma levels. In contrast to HT-nEIH and UT (p < 0.05), HT-EIH showed a smaller increase in ANF concentration between rest and maximal exercise (HT-EIH: 8.12 +/- 0.69 vs. 14.1 +/- 1.86 pmol x l (-1); HT-nEIH: 10.46 +/- 1 vs. 18.7 +/- 1.8 pmol x l (-1); UT: 6.23 +/- 0.95 vs. 20.38 +/- 2.79 pmol x l (-1)). During the recovery, ANF levels decreased significantly in HT-nEIH and UT groups (p < 0.05). Electrolyte values increased in all groups during exercise but were higher in both trained groups. In conclusion, this study suggested that ANF response to exercise may be important for exercise-induced hypoxemia.     

Atrial natriuretic peptide and the renin-aldosterone axis during exercise in man

Under non-exercise conditions, atrial natriuretic peptide (ANP) elevation suppresses plasma renin activity (PRA) and aldosterone (PA). A similar effect of ANP on PRA-PA during exercise has been suggested but not demonstrated. We measured ANP, PRA, PA, plasma potassium (K+), and changes in plasma volume (PV) and blood volume (BV) at rest and during incremental cycle ergometer exercise to exhaustion in ten healthy males. Plasma concentrations (mean +/- SE) of hormones and electrolytes increased (P less than 0.05) during exercise: ANP (68 +/- 14 to 207 +/- 48 pg.ml-1), PA (11.2 +/- 2.2 to 18.8 +/- 3.4 ng.dl-1), PRA (5.1 +/- 1.1 to 8.2 +/- 1.6 ng.ml-1.90 min-1), and K+ (4.2 +/- 0.1 to 5.5 +/- 0.1 mEq). PV and BV declined, reaching maximal deflections from baseline during the 100% stage (12.9 +/- 1.5 and 8.4 +/- 0.8% decreases, respectively). There were positive correlations between ANP and PRA (r = 0.58; P less than 0.01), ANP and PA (r = 0.56; P less than 0.01), and PRA and PA (r = 0.80; P less than 0.001). Increases in K+ did not correlate with increases in PA. The fall in PV correlated with elevations in PRA (r = -0.67; P less than 0.01) and PA (r = -0.58; P less than 0.01), and the fall in BV correlated with elevations in PRA (r = -0.62; P less than 0.01) and PA (r = -0.44; P less than 0.02). ANP production was related to exercise intensity (gauged by heart rate response; r = 0.58; P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of hydration on plasma vasopressin, renin, and aldosterone responses to head-up tilt

If plasma vasopressin (PVP), plasma renin (PRA), and plasma aldosterone (PA) responses to change in posture are mediated only by alterations in intrathoracic baroreceptor activity, hydration status should have minimal influence on these responses. To test this hypothesis, six male subjects underwent 45 min of 70 degree head-up tilt (HUT) following 26 h dehydration, and again, 105 min later, following rehydration. Compared with preceding supine hydrated control values, PVP, PRA, and PA increased (p less than 0.001) during dehydrated HUT, but only PVP and PRA increased during rehydrated HUT (p less than 0.001). The dissociation during rehydrated HUT of PRA and PA may have been related more to the reduction (p less than 0.001) in plasma potassium concentration than to the accompanying decrease (p less than 0.001) in plasma osmolality and sodium concentration. Although increases in PVP and PRA during HUT were attenuated (p less than 0.01) following rehydration, this attenuation was associated with the absence of symptoms of overt hypotension following rehydration. However, since rehydration did not abolish the increases in PVP and PRA induced by HUT, it is concluded that the present observations support the concept of intrathoracic baroreceptor involvement in the regulation of vasopressin secretion and renin release.     

Acute hypoxia-induced diuresis in rats.

Acute hypoxia elicits diuresis, natriuresis, and hypotension in many mammalian species, but the cause of this effect remains unclear. The present study, using chronically instrumented rats, was undertaken to assess a possible role of atrial natriuretic factor (ANF) in these hypoxic responses. Acute hypoxia (10.5% O2) increased urine output and sodium and potassium excretion. Systemic arterial blood pressure fell during acute hypoxia. Levels of ANF significantly increased with acute hypoxia. The plasma levels of ANF during acute hypoxia were similar to those found following bolus doses of exogenous ANF which are known to cause diuresis, natriuresis and a fall in blood pressure. Increased ANF levels may play a role in mediating physiologic responses to hypoxia in the rat.     

Correlation of plasma norepinephrine and plasma atrial natriuretic factor during lower body negative pressure

Plasma atrial natriuretic factor (ANF) is released in proportion to intra-atrial pressures. Plasma norepinephrine (NE) levels are considered to be an indirect reflection of sympathetic tone. These two mediators were studied during human regulation of intravascular volume in the course of exposure to fluid shifts associated with a model of gravitational stress, lower body negative pressure (LBNP.) Blood was drawn from 10 normal subjects before and after exposure to 2 min of a graduated increase in LBNP to a level of 55 mmHg followed by 5 min at 55 mmHg. Plasma ANF was measured by RIA and catecholamines by HPLC-ECD. NE increased from 358 +/- 44 (S.E.M) pg/ml to 511 +/- 48 pg/ml (p = 0.03.) Although ANF only decreased from 27.3 +/- 2.4 pg/ml to 23.5 +/- 2.9 pg/ml (p = 0.33,) a statistically significant negative correlation was observed (r = -0.70, p = 0.02) between the changes in NE and ANF induced by LBNP. The modelling of physiologic responses to gravitational stress in this experiment revealed a negative correlation between changes in sympathetic tone (as reflected by plasma NE) and ANF levels.     

Aerobic fitness: I. Response of volume regulating hormones to head-down tilt.

We investigated the relationship of aerobic fitness to the response of volume-regulating hormones to acute simulated microgravity. Six untrained (UT) and six endurance-trained (ET) healthy young males were studied in the head-down tilt (HDT) position of -6 degrees for 4 h. Peak oxygen uptake (VO2peak) and plasma volume (PV) were significantly greater in the ET (VO2peak = 61.7 +/- 1.6 ml.min-1.kg-1 and PV = 53.1 +/- 2.8 ml.kg-1) than in the UT (VO2peak = 38.4 +/- 1.7 ml.min-1.kg-1 and PV = 38.8 +/- 1.0 ml.kg-1). Plasma concentrations of atrial natriuretic peptide (ANP), arginine vasopressin (AVP), norepinephrine (NE), renin activity (PRA), and aldosterone (PA) were measured prior to HDT and at minutes 2, 5, 15, 30, 60, 120, 180, and 240 during HDT. PRA and PA significantly decreased during the time of HDT in both groups. The changes in ANP and NE concentrations were not significantly different between the groups nor across time. However, in the ET subjects, the changes in PRA and NE were significantly correlated with the changes in ANP (r = 0.49, P less than 0.01; and r = 0.86, P less than 0.001, respectively); in the UT subjects, the changes in AVP, PRA, and PA were significantly associated with changes in NE (r = 0.34, P less than 0.03; and r = 0.59; and r = 0.53, P less than 0.01, respectively). PV significantly decreased during HDT, and was primarily related to the decrease in PA in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Plasma renin activity and aldosterone: correlations with moderate hypohydration

Adult male test subjects (n = 16) were assigned to one of three clothing configurations (Army fatigues, fatigues with impermeable chemical protective garments, and fatigues with protective garments plus protective masks) prior to exercise (level treadmill, 1.11 m/s, 50 min/h, 6 h) in a moderate (wet bulb globe temperature, WBGT = 23 degrees C) environment with ad lib water consumption. When protective masks were worn, two through-mask drinking systems were evaluated: the current gravity-fed system for fluid delivery and a new system utilizing a small hydraulic pump (Fist-Flex). Antecubital blood samples were taken prior to the start of and subsequent to the completion of exercise and analyzed for fluid-electrolyte regulatory hormones. During all trials with chemical protective garments, plasma renin activity (PRA) and aldosterone levels (PA) were significantly (p less than 0.05) elevated following the exercise protocol while neither was affected during exercise in fatigues only. Individual hypohydration levels during all trials ranged from low (0.84%) to moderate (4.04%). Levels of PRA were closely correlated (r = 0.635, t = 4.35, p less than 0.001) with hypohydration as measured by percentage of body weight lost during the 6 h trial. Likewise, PA was also correlated (r = 0.47, t = 2.81, p less than 0.01) with body weight loss. We concluded from this study that PRA and PA responses were exacerbated in moderate environments by the additional heat stress, sweat rate, and dehydration caused by the impermeable garments. Further, the logistical difficulty inherent in delivering fluid through the chemical protective mask reduced voluntary consumption, increased hypohydration, and elicited the greatest elevations in PRA and PA.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hormonal and metabolic changes during a strenuous tennis match. Effect of ageing

The effect of a strenuous tennis match was studied in 9 young (21.2 +/- 1.9 yr) and 10 veteran women players (46.5 +/- 1.3 yr) of equivalent skill. Each match was carried out during the summer (ambient temperature 27 +/- 1 degree C), as an official competition, under conditions as similar as possible. Heart rate (HR) was monitored throughout the match, weight loss was evaluated and pre- and post-match values of haematocrit, plasma lactate, free fatty acid (FFA), glycemia, ionogram, norepinephrine (NOR), epinephrine, arginine vasopressin (AV) concentrations and plasma renin activity (PRA) were measured. Plasma volume was calculated. While mean HR remained steady in young players, it increased progressively in veteran players as the match went on and reached a very high level towards the end of the match. When post-match values were compared to pre-match values, the mean results were: no substantial changes in plasma lactate and electrolyte concentrations, a large increase in FFA, no increase in epinephrine, a moderate rise in NOR and a large increase in PRA and AV. Despite a similar weight loss, a large drop in plasma volume occurred only in veteran players, who also showed FFA and AV values greater than in young players. During these strenuous matches the large response of hormones which control body fluid probably contributed to the limiting of changes in water and electrolyte balances. However, under similar conditions marked differences occurred as a function of ageing concerning the control of plasma volume.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cardiovascular and endocrine responses to 90 degree tilt during a 35-day saturation dive to 46 and 37 ATA

INTRODUCTION: Hyperbaria-induced diuresis is accompanied by decreased basal and stimulated release of arginine vasopressin (AVP) and decreased blood volume possibly contributing to the reported orthostatic intolerance. Since hyperosmolality is not a consistent finding, the explanation of blood volume reduction at hyperbaria must involve an osmotic component to the diuresis. Investigations of a possible involvement of atrial natriuretic peptide (ANP) to the hyperbaric diuresis have revealed mixed results. METHODS: Urinary excretion of electrolytes, AVP, and aidosterone were measured in four male subjects studied at 1 atmosphere absolute (ATA) and at 46 and 37 ATA (0.5 atmospheres pressure O2: 5% N2: remainder He) during a 35-d saturation dive. Also, the supine and 90 degrees tilt-stimulated plasma levels of AVP, plasma renin activity (PRA), and aldosterone, and the suppressed responses of ANP and the cardiovascular responses to tilt were determined at these pressures. RESULTS: Tilt-stimulated levels of PRA were increased two- to threefold and the AVP response was eliminated throughout hyperbaria, except in two episodes of tilt-induced syncope where AVP was elevated 10- to 20-fold. This pattern supports most previous reports. Contrary to some reports, both supine and tilt-suppressed levels of ANP were reduced by about 50% at all three tilt experiments conducted at hyperbaria compared to predive control values. DISCUSSION: These results suggest an altered ANP response at pressures of 37 ATA or greater, which is consistent with an appropriate ANP response to blood volume reduction and further suggest that the hyperbaric diuresis is not dependent on increased ANP.     

Renin angiotensin aldosterone system and ACE I/D gene polymorphism in high-altitude pulmonary edema

INTRODUCTION: People who visit high altitude are exposed to a stressful environment, and many of them suffer from altitude-induced conditions, including high altitude pulmonary edema (HAPE). We investigated the renin angiotensin aldosterone system (RAAS) and the possible association of angiotensin converting enzyme (ACE) insertion/deletion (I/D) gene polymorphism in the development of HAPE in Indian men. METHODS: Subjects were all low-altitude natives: 19 men who developed HAPE within 1-3 d of arrival at 3000 to 3800 m (patients); and 20 age-matched men who did not develop HAPE during a period of a month or more at > or = 3500 m (controls). We recorded the arterial oxygen saturation (Sao2), heart rate (HR), and blood pressure (BP) of both groups and measured their levels of plasma renin activity (PRA), ACE, aldosterone, and serum electrolytes. Polymerase chain reaction was used to investigate a 287 base pair alu repeat sequence I/D polymorphism in the ACE gene. RESULTS: Compared with controls, patients showed a significantly lower Sao2 and a higher HR. They also had significantly higher plasma PRA, aldosterone, ACE, and serum sodium (Na+) and potassium (K+). No significant difference was observed in ACE I/D allele frequencies. DISCUSSION: The results suggested that RAAS is involved in the development of HAPE in low-altitude natives, but there is no association of ACE I/D gene polymorphism with HAPE.     

Results of a 4-week head-down tilt with and without LBNP countermeasure: I. Volume regulating hormones.

The volume regulating hormones were studied during a 4-week head-down tilt (CNES HDT) in five subjects with and without (controls) lower body negative pressure (LBNP). LBNP was applied 3 times a day for 3 weeks, 4 times a day for 4 d, and 6 times a day for 3 d the last week. In both groups we observed a significant decrease in body weight (3% in controls, 0.8% in LBNP), a significant increase in plasma renin activity and aldosterone (with an amplification of their rhythms), and a significant decrease in norepinephrine with no difference between the two groups. The only major hormonal difference was observed for atrial natriuretic factor (ANF), which decreased significantly in the control group and increased in the LBNP group. These results are compared with the improvement in orthostatic tolerance (OT) after HDT in the LBNP group in the same protocol (17). We conclude that many factors could be involved in the improvement of OT. The results suggest that better conservation of plasma volume in the LBNP group might have prevented a decrease in ANF. Whether ANF plays a role in the regulation of baroreceptor reflex with an improvement in OT is currently unknown.     

Metabolic changes during volleyball matches

Urinary and/or serum concentrations of electrolytes (sodium, potassium, calcium, magnesium), hormones (aldosterone, cortisol, catecholamines), and metabolic parameters (lactate, glucose, free fatty acids) were determined during different volleyball matches. While [Na+]s was slightly increased-not exceeding the hemo-concentration effect-[K+]s, and [Ca2+]s were diminished after the matches. Due to a lowered glomerular filtration rate (GFR), urinary excretion of water, sodium, and potassium was decreased. In addition, the tubular resorption and secretion of fluid and electrolytes was influenced by different hormones leading to a lowered [Na+]u and an increase of [K+]u after exercise. Low concentrations of lactate (2.54 +/- 1.21 mmol/l) during and after the matches and an increase of [FFA]s indicate that energy during the short exercise periods (9 s) is mainly supplied by a breakdown of creatine phosphate, while aerobic pathways restore the energy sources during the resting periods (12 s). Serum concentrations of aldosterone and cortisol as well as the excretion of adrenaline are enhanced on the same scale as after endurance sports. The excretion of noradrenaline corresponds to values during exercise of high intensity.     

Training-overtraining: performance, and hormone levels, after a defined increase in training volume versus intensity in experienced middle- and long-distance runners.

Performance and hormones were determined in eight middle- and nine long-distance runners after an increase in training volume (ITV, February 1989) or intensity (ITI, February 1990). Seven runners participated in both studies. The objective was to cause an overtraining syndrome. The mean training volume of 85.9 km week-1 increased within 3 weeks to 176.6 km week-1 during ITV and 96-98% of training volume was performed as long-distance runs at mean(s.d.) 67(8)% of maximum capacity. Speed endurance, high-speed and interval runs averaging 9 km week-1 increased within 3 weeks to 22.7 km during ITI, and the total volume increased from 61.6 to 84.7 km. A plateau in endurance performance and decrease in maximum performance occurred during ITV, probably due to overtraining, with performance incompetence over months. Nocturnal catecholamine excretion decreased markedly (47-53%), contrary to exercise-related plasma catecholamine responses, which increased. Resting and exercise-related cortisol and aldosterone levels decreased. Improvement in endurance and maximum performance occurred during ITI indicating a failure to cause an overtraining syndrome in ITI. Decrease in noctural catecholamine excretion was clearly lower (9-26%), exercise-related catecholamine responses showed a significant decrease, cortisol and aldosterone levels remained almost constant, exercise-related prolactin levels decreased slightly. There were no differences in insulin, C-peptide, free testosterone, somatotropic hormone (STH), follicle stimulating hormone (FSH), luteinizing hormone (LH), thyroid stimulating hormone (TSH), tri-iodothyronine (T3) and thyroxine (T4). The decrease in nocturnal catecholamine excretion during ITV might indicate a decrease in intrinsic sympathetic activity in exhausted sportsmen. But it remains open whether this reflected a central nervous system incompetence.