Plasma, urinary and fecal potassium changes in athletes during ambulatory, periodic, and continuous hypokinetic conditions

Clinical Biochemistry, Vol. 33, No. 1, 37– 46, 2000 Copyright © 2000 The Canadian Society of Clinical Chemists Printed in the USA. All rights reserved 0009-9120/00/$–see front matter

PII S0009-9120(99)00062-4

Plasma, Urinary and Fecal Potassium Changes in Athletes During Ambulatory, Periodic, and Continuous Hypokinetic Conditions YAN G. ZORBAS,1 VASSILY J. KAKURIN, VIKTOR B. AFONIN,1 KIRILL P. CHARAPAKHIN, VLADIMIR L. YARULLIN,1 and VICTOR A. DEOGENOV 1

Kosmic Biology and Medicine Institute, Krasno Selo, Sofia 1404, Bulgaria

Objectives: Prolonged hypokinesia (HK) induces significant electrolyte changes, but little is known about the effect of prolonged periodic hypokinesia on plasma, urinary, and fecal K. The aim of this study was to measure potassium (K) changes during prolonged periodic (PHK) and continuous (CHK). Design and methods: Studies were done during the pre HK and HK periods. Thirty male athletes were chosen as subjects. They were divided equally into three groups: unrestricted ambulatory control subjects (UACS), continuously hypokinetic subjects (CHKS), and periodically hypokinetic subjects (PHKS). The CHKS group was kept on a running distance of 0.7 km/day, while the PHKS group kept on a running distance of 0.7 and 11.7 km/day for 5 days and 2 days per week, respectively. The UACS group was on a running distance of 11.7 km/day. Results: The following were measured: fecal K excretion; urinary K; sodium (Na) and chloride (Cl) excretion; plasma K; Na and Cl concentration; plasma renin activity (PRA) and plasma aldosterone (PA) concentration; physical characteristics; and peak oxygen uptake. Fecal K, urinary K, Na and Cl excretion, plasma K, Na and Cl concentration, and PRA and PA concentration, increased significantly (p ⱕ 0.01) in the CHKS and PHKS groups when compared with the UACS group. Body weight and VO2 peak decreased significantly (p ⱕ 0.01) in the CHKS group, while body weight increased and VO2 peak decreased significantly (p ⱕ 0.01) in the PHKS group when compared with the UACS group. The measured parameters changed much more in the PHKS group than in the CHKS group. By contrast, the measured parameters did not change significantly in the UACS group when compared with the baseline control values. Conclusion: It was shown that prolonged PHK and CHK induce significant plasma and excretory K changes; however, plasma and excretory K changes were much greater in the PHKS group than in the CHKS group. It was concluded that the greater the stability of muscular activity, the smaller the plasma, urinary, and fecal K changes during prolonged HK. Copyright © 2000 The Canadian Society of Clinical Chemists

KEY WORDS: periodic hypokinesia; potassium; sodium; chloride; renin; aldosterone; peak oxygen uptake; body weight.

Correspondence: Viktor A. Deogenov, Hypokinetic Physiology Lab, European Institute of Environmental Cybernetics, Odos Agias Sophias 81, GR-162 32 Athens, Greece. Manuscript received April 13, 1999; revised July 30, 1999; accepted August 5, 1999. CLINICAL BIOCHEMISTRY, VOLUME 33, FEBRUARY 2000

Introduction ypokinesia has a dual effect on animal and human organisms. Hypokinesia is associated with a reduction in the rate of flow of afferent and, thus, efferent information, and the organism of animals and humans is deprived of their constant regulatory influence. Any change from a state of increased to decreased muscular activity or any alteration of muscular activity from a state of continuous to periodic HK acts as a hypokinetic stress, and the greater the difference between these conditions, the stronger the hypokinetic effect. Technical progress places increasing number of individuals under conditions that create the prerequisite for different forms of hypokinesia (HK), in particular periodic HK, that is, decreased muscular activity alternated with regular or irregular increased muscular activity. Despite the extensive attention given to physical exercise and sports, a disproportion arises and grows between mental activity, which is inevitably on the increase, and physical activity, which becomes less and less mandatory. Yet, very few studies have been devoted to the significance of this shift and, in particular, to the trend of PHK towards metabolic electrolyte changes. It is known that stable volume, osmotic concentration and electrolyte composition of internal fluids is a prerequisite for animals and humans to be in a better physical state and highly efficient condition. However, the physiologic and biochemical systems that regulate the concentration of each electrolyte in blood and other endogenous fluids, the equilibrium between input and output of electrolytes and thus electrolyte balance and total electrolyte concentration of the body is significantly affected during HK (1– 6). Hypokinetic induced metabolic electrolyte changes may play a significant part in the pathogenesis of several disorders related to prolonged HK. It is known that prolonged HK is associated with increase excretion of electrolytes in urine and feces (1– 6). Use of electrolyte supplements made

H

37

ZORBAS

ET AL.

TABLE 1 Anthropometric and Peak Oxygen Uptake Changes of Athletes During Prolonged Periodic and Continuous Hypokinesia (Mean ⫾ SD) Groups of Subjects Examined parameters Age (years) Height (cm) Body mass (kg) Body fat (%) Fat-free body mass (kg) VO2 peak mL/kg⫺1min⫺1

Testing periods

Ambulatory control n ⫽ 10

Continuous hypokinetic n ⫽ 10

Periodic hypokinetic n ⫽ 10

before before before after before after before after before after

25.8 ⫾ 7.0 177.0 ⫾ 6.5 74.9 ⫾ 8.5 75.5 ⫾ 6.0 8.5 ⫾ 1.3 6.7 ⫾ 1.2 68.6 ⫾ 6.0 70.5 ⫾ 8.6 67.0 ⫾ 6.0 67.3 ⫾ 5.5

24.7 ⫾ 6.5 175.6 ⫾ 7.7 75.7 ⫾ 6.0 68.1 ⫾ 8.6* 9.4 ⫾ 1.2 3.0 ⫾ 1.3* 68.6 ⫾ 7.6 66.4 ⫾ 6.6 65.5 ⫾ 8.0 52.1 ⫾ 6.6*

23.9 ⫾ 8.0 174.6 ⫾ 6.0 76.0 ⫾ 7.5 83.4 ⫾ 6.6*† 8.5 ⫾ 1.3 15.0 ⫾ 2.5*† 69.6 ⫾ 6.0 71.2 ⫾ 7.5 64.9 ⫾ 6.4 59.3 ⫾ 7.5*†

In this table, “before” means at the end of the pre-HK and “after” means at the end of the CHK and PHK periods. Significant differences (*p ⱕ 0.01) between ambulatory control and hypokinetic groups of subjects. Significant differences (†p ⱕ 0.01) between continuous and periodic hypokinetic groups of subjects.

it possible to establish a significant excretion of electrolytes in urine and feces despite the presence of decreased total electrolyte concentration of the body and negative electrolyte balance (1– 6). The hypothesis was expounded by the authors that negative electrolyte balance and decreased total electrolyte concentration of the body during prolonged HK could be attributable to the impossibility of the body to retain electrolytes due to several factors. Decreased total electrolyte concentration of the body during prolonged HK is shown by increased serum or plasma electrolyte concentration and not by decreased as it happens in clinical situations. The results obtained on electrolyte metabolism in athletes during prolonged HK have suggested the presence of another mechanism that might influence the control and regulation of electrolyte metabolism (1– 6). Unfortunately, electrolyte changes during PHK are not as well understood as for other forms of HK. This is mainly attributable to the fact that most investigative work on electrolyte metabolism in animals and humans has been done under conditions that did not include the PHK factor. Some biochemical and physiologic studies have been done on animals and humans during prolonged PHK (7,8). It was shown that prolonged PHK induces much greater physiologic and biochemical changes than CHK. The reason for this reaction remains unclear. Because more and more people are subjected to PHK due to sedentary living and working conditions on the one hand and increased physical exercise for improving their physical fitness on the other, and because it is not known whether PHK induces more or less electrolyte changes than CHK, it is important to study electrolyte changes during prolonged PHK. Thus, the aim of this study was to determine whether between the PHK and CHK conditions are any differences regarding the intensity of plasma, urinary, and fecal K changes during prolonged HK. 38

Materials and methods SUBJECT

SELECTION

Thirty male athletes ranging in age from 20 –26 years gave informed consent to take part in the study after a verbal and written explanation of the methods and risks involved was given. Financial incentives were used to encourage compliance with the study protocol. Procedures were previously reviewed and approved by the Committee for the Protection of Human Subjects. All athletes had trained as long distance runners for the last 3 to 5 years, at an average of 11.7 km/day and had a speed of 10.3 km/hour. Physical characteristics of the subjects are given in Table 1. EXPERIMENTAL

DESIGN

Subjects were on a metabolic diet for 30 days during the pre-HK period and 364 days during the CHK and PHK periods. Portions of food provided were weighed, and uneaten portions of the measured intake of food were weighed. The diet was then maintained for the remainder of the study and was controlled for calories, fluid, and K intakes with food. Dietary composition of selected nutrients is presented in Table 2. Assignment of the subjects into three categories was done randomly. Conditions of the three groups are as follows: Group 1: Ten athletes experienced no changes in their professional training and routine daily activities, and their muscular activity was maintained at an average of 11.7 km/day. They served as unrestricted ambulatory control subjects (UACS). Group 2: Ten athletes were subjected to changes in their professional training and routine daily activities, and their muscular activity was restricted CLINICAL BIOCHEMISTRY, VOLUME 33, FEBRUARY 2000

POTASSIUM CHANGES DURING PERIODIC HYPOKINESIA

TABLE 2 Dietary Intakes of Athletes During Prolonged Periodic and Continuous Hypokinesia (Mean ⫾ SD) Examined parameters

Testing periods

Calories (kcal) Proteins (g) Lipids (g) Carbohydrates (g) Sodium (mg) Potassium (mg) Calcium (mg) Magnesium (mg) Fluid intakes (mL)

before after before after before after before after before after before after before after before after before after

Ambulatory control n ⫽ 10

Continuous hypokinetic n ⫽ 10

Periodic hypokinetic n ⫽ 10

3635 ⫾ 365 3610 ⫾ 325 123 ⫾ 17.0 124 ⫾ 15.5 115 ⫾ 16.3 114 ⫾ 15.2 477 ⫾ 26.4 480 ⫾ 25.6 6725 ⫾ 13.5 6730 ⫾ 11.0 4380 ⫾ 440.3 4382 ⫾ 451.0 1676 ⫾ 248.3 1680 ⫾ 252.6 645 ⫾ 75 650 ⫾ 85 3974 ⫾ 687 3980 ⫾ 620

3655 ⫾ 371 2577 ⫾ 264* 127 ⫾ 16.6 110 ⫾ 17.0 117 ⫾ 17.2 99 ⫾ 16.4 485 ⫾ 24.3 425 ⫾ 22.5 6745 ⫾ 12.0 5940 ⫾ 11.4 4387 ⫾ 451.0 3860 ⫾ 325.3 1688 ⫾ 260.2 1473 ⫾ 234.2 655 ⫾ 84 576 ⫾ 72 3980 ⫾ 649 2780 ⫾ 452*

3648 ⫾ 346 3989 ⫾ 354*† 125 ⫾ 18.5 128 ⫾ 16.6 114 ⫾ 15.3 119 ⫾ 17.5 480 ⫾ 21.2 499 ⫾ 25.3 6735 ⫾ 13.6 6910 ⫾ 12.6 4383 ⫾ 432.2 4411 ⫾ 427.4 1673 ⫾ 252.0 1731 ⫾ 242.1 653 ⫾ 72 667 ⫾ 85 3975 ⫾ 623 4397 ⫾ 586*†

In this table the data represents the average of various analyses done during the different interventions. In this table , “before” means at the end of the pre-HK period and “after” means at the end of the CHK and PHK periods. Significant differences (*p ⱕ 0.01) between ambulatory control and hypokinetic groups of subjects. Significant differences (†p ⱕ 0.01) between continuous and periodic hypokinetic groups of subjects.

continuously to an average of 0.7 km/day for 364 days. They served as continuously hypokinetic subjects (CHKS). Group 3: Ten athletes were subjected to changes in their professional training and routine daily activities, and their muscular activity was restricted periodically. That is, they were maintained under an average running distance of 0.7 and 11.7 km/ day for 5 days and 2 days per week, respectively, for 364 days. They served as periodically hypokinetic subjects (PHKS). SIMULATION

OF

CHK

Subjects were admitted to the Metabolic Study Unit at the Hospital, where the studies were done. For the simulation of the hypokinetic effect, the number of kilometers taken per day was restricted to an average of 0.7. Activities allowed were those that approximated the normal routines of sedentary individuals. Climbing stairs and other activities that required greater effort were not allowed. All subjects were mobile and allowed outside the hospital ground. SIMULATION

OF

PHK

Conditions for the simulation of PHK during the 5 days of the week were the same as those with CHK; that is, the PHKS group during 5 days of the week (Monday to Friday) was on an average running distance of 0.7 km/day. For the other 2 days of the week (Saturday and Sunday), the conditions for the CLINICAL BIOCHEMISTRY, VOLUME 33, FEBRUARY 2000

PHKS group were the same as those for the UACS group; that is, the PHKS group during these 2 days of the week was allowed to resume their professional training and routine daily activities and run an average distance of 11.7 km/day. Thus, muscular activity of the PHKS group was restricted only during the initial 5 days of the week and unrestricted during the other 2 days of the week. SAMPLE

COLLECTION

Samples were collected every 3 successive days during the pre-HK, CHK, and PHK periods and the mean ⫾ SD of the measurements are presented during the pre-HK period and every 60 days during the PHK and CHK periods. Samples of blood were taken at rest and before any meals. Blood samples were collected with disposable polypropylene syringes (Becton-Dickinson, Rutherford, NJ, USA) under the same conditions between 6 and 9 AM, without stasis, and after the subjects had been sitting for about 30 min. Samples were 10 to 15 mL. To obtain plasma, blood samples were transferred to polypropylene tubes (Bio-Rad Laboratories, Richmond, CA, USA) containing sodium heparin (Invenex Laboratories, Melrose Park, IL, USA). The samples were centrifuged immediately at 10,000 ⫻ g using glass capillary pipettes washed in hydrochloric acid and deionized water. Aliquots for K, Na and Cl, PRA, and PA concentrations were stored at ⫺20° C. All samples from each subject assayed in the same run. Twenty-four hour urine collections were refrigerated at ⫺4° C until needed for K, Na, and Cl. Feces were collected in 39

ZORBAS

plastic bags, then dried, weighed, and refrigerated at ⫺20° C for K analysis. Fecal samples were washed in a mixture of nitric and perchloric acids, and diluted as necessary with deionized distilled water. ELECTROLYTE

MEASUREMENTS

All samples were analyzed in duplicate and appropriate standards were used for all measurements: Plasma, urinary and fecal K, and urinary and plasma Na were measured using a flame photometer (Perkin-Elmer Corp., Norwalk, CT, USA) and urinary and plasma Cl was measured using a BuchlerCotlove Chloridometer (Laboratory Devices, Holliston, MA, USA). RADIOIMMUNOASSAY

MEASUREMENTS

All samples were analyzed in duplicate and appropriate standards were used for all measurements. Plasma renin activity was optimally assessed at a pH of 6.0 at 37° C during a 1-h incubation period using radioimmunoassay test kits purchased from New England Nuclear Corp. (Billerica, MA, USA). Plasma aldosterone concentration was measured using radio immunoassay test kits purchased from Diagnostics Products Corp. (Los Angeles, CA, USA). ANTHROPOMETRIC

MEASUREMENTS

Height (in centimeters) and weight (in kilograms) were measured using a beam scale with attached stadiometer. Subjects wore nylon training shorts during the measurements. Percentage body fat was calculated using the following skinfolds (in millimeters): biceps, triceps, subscapular, abdominal, chest, and suprailiac as has been described in the text of Lohman et al. (9). Body fat was calculated using the equation of Brozek (10). All measurements were done by the same experimenter. PEAK

OXYGEN UPTAKE MEASUREMENTS

Respiration parameters were recorded continuously during the tests using an automated system (Beckman MMC; Beckman, Fullerton, CA). Room temperature was controlled at 18 –20° C. Oxygen uptake was calculated over minute ⫻ intervals. The highest value during the tests was taken as peak oxygen uptake. Peak oxygen uptake tests were done on a treadmill. The graded treadmill test protocol began with 10 min warmups at a workload that elicited a heart rate of 110 –130 bpm. Treadmill speed increased at 5-min intervals until a speed of 10 –13 mph was reached, after which the grade was increased 1% every 5 min until the subject reached exhaustion. The peak oxygen uptake tests were administered blindly by a third party who had no knowledge of the conditions of the participants. 40

ET AL.

STATISTICAL

ANALYSIS

Data were analyzed by performing a one- or twoway analysis of variance (ANOVA) corrected for repeated measures. Post hoc analyses were done using the Tukey-Kramer multiple range tests. A format analysis was done to determine the shape of changes. In all comparisons, differences were considered statistically significant when p ⱕ 0.01. The results are presented as means ⫾ SD. Results PREHYPOKINETIC

REACTIONS

During the pre-HK period, urinary, fecal and plasma K, urinary and plasma Na and Cl, PRA, and PA did not change significantly in the control and hypokinetic groups of subjects (Tables 3, 4, and 5). Peak oxygen uptake, body weight, body fat, fat-free body mass, and food and water intakes remained stable during the pre-HK period in the control and hypokinetic groups of subjects (Tables 1 and 2). The values of the measured parameters were typical to the values found in trained athletes on the same dietary intakes of K and in a similar situation. HYPOKINETIC

REACTIONS

During the HK period, all subjects were in a satisfactory condition and none of the subjects were complaining of any severe discomfort or manifested any serious disorders. During the initial 30 days of the HK period, one athlete who was submitted to PHK and one athlete who was submitted to CHK experienced chest pain, heart burns, dyspepsia, dizziness, heaviness in the head, and pain in the joints of the upper and lower extremities. However, as the duration of the HK period increased, all signs and symptoms disappeared spontaneously in the PHKS and CHKS groups. ANTHROPOMETRIC

AND PEAK OXYGEN UPTAKE CHANGES

Peak oxygen uptake, body weight, body fat, and fat-free body mass remained stable in the UACS group when compared with the baseline control values (Table 1). In the CHKS group, body weight, body fat, and peak oxygen uptake decreased significantly (p ⱕ 0.01), while fat-free body mass did not decrease significantly when compared with the UACS group (Table 1). By contrast, in the PHKS group body weight and body fat increased significantly (p ⱖ 0.01), fat-free body mass increased insignificantly, while peak oxygen uptake decreased significantly (p ⱕ 0.01) when compared with the UACS and CHKS groups (Table 1). FOOD

AND WATER INTAKES

In the UACS group, food and water intakes remained stable when compared with the baseline CLINICAL BIOCHEMISTRY, VOLUME 33, FEBRUARY 2000

POTASSIUM CHANGES DURING PERIODIC HYPOKINESIA

TABLE 3 Fecal Potassium and Urinary Excretion of Electrolytes of Athletes During Prolonged Periodic and Continuous Hypokinesia (Mean ⫾ SD)

Testing days

Fecal loss of potassium (mEq/day)

Unrestricted ambulatory control subjects, n ⫽ 10 Baseline 22.7 ⫾ 2.2 60th 20.1 ⫾ 2.0 120th 21.9 ⫾ 2.2 180th 19.0 ⫾ 2.6 240th 21.5 ⫾ 2.4 300th 19.6 ⫾ 2.5 364th 21.7 ⫾ 2.0 Continuous hypokinetic subjects, n ⫽ 10 Baseline 21.6 ⫾ 2.5 60th 30.0 ⫾ 2.6* 120th 22.2 ⫾ 3.0* 180th 35.0 ⫾ 2.7* 240th 24.9 ⫾ 3.3* 300th 38.0 ⫾ 2.6* 364th 30.8 ⫾ 2.7* Periodic hypokinetic subjects, n ⫽ 10 Baseline 22.0 ⫾ 2.2 60th 35.7 ⫾ 4.0* 120th 27.0 ⫾ 3.3* 180th 46.7 ⫾ 2.5* 240th 35.4 ⫾ 2.7* 300th 47.0 ⫾ 2.5* 364th 36.2 ⫾ 2.8*

Urinary excretion of electrolytes Potassium (mEq/day)

Sodium (mEq/day)

Chloride (mEq/day)

83 ⫾ 14 77 ⫾ 10 85 ⫾ 11 75 ⫾ 8 80 ⫾ 10 74 ⫾ 9 82 ⫾ 11

187 ⫾ 21 179 ⫾ 16 185 ⫾ 18 177 ⫾ 21 175 ⫾ 15 183 ⫾ 20 177 ⫾ 14

150 ⫾ 12 144 ⫾ 17 151 ⫾ 13 147 ⫾ 15 150 ⫾ 12 144 ⫾ 16 148 ⫾ 14

85 ⫾ 12 110 ⫾ 19* 101 ⫾ 20* 129 ⫾ 26* 107 ⫾ 18* 141 ⫾ 22* 115 ⫾ 17*

185 ⫾ 22 230 ⫾ 23* 207 ⫾ 20* 277 ⫾ 25* 241 ⫾ 22* 311 ⫾ 24* 285 ⫾ 20*

155 ⫾ 14 195 ⫾ 21* 173 ⫾ 25* 227 ⫾ 20* 207 ⫾ 19* 260 ⫾ 22* 239 ⫾ 24*

83 ⫾ 15 119 ⫾ 25* 103 ⫾ 22* 147 ⫾ 24* 126 ⫾ 21* 165 ⫾ 26* 143 ⫾ 23*

180 ⫾ 17 262 ⫾ 22* 231 ⫾ 24* 318 ⫾ 20* 282 ⫾ 25* 360 ⫾ 23* 330 ⫾ 26*

151 ⫾ 19 217 ⫾ 24* 193 ⫾ 17* 264 ⫾ 22* 221 ⫾ 18* 297 ⫾ 26* 249 ⫾ 20*

Significant differences (*p ⱕ 0.01) between ambulatory control and hypokinetic groups of subjects. Significant differences (†p ⱕ 0.01) between continuous and periodic hypokinetic groups of subjects.

control values (Table 2). The CHKS group showed a significant decrease in their food and fluid intakes during the initial 30 days of the CHK period (Table 2); however, as the duration of the CHK period increased, food and water intakes increased progressively, but they stabilized significantly (p ⱕ 0.01) below the values observed in the UACS group. By contrast, food and water intakes increased significantly (p ⱕ 0.01) in the PHKS group when compared with the CHKS group (Table 2); during the resumption of muscular activity, food and water intakes increased even further in the PHKS group when compared with the CHKS group.

ences were observed regarding the intensity of urinary and plasma K, Na, and Cl changes (Tables 3 and 4). The maximum urinary K, Na, and Cl excretion always corresponded to the maximum plasma K, Na, and Cl concentration. During the CHK and PHK periods, urinary electrolyte excretion and plasma electrolyte concentration increased progressively while showing a pattern of a wave-like changes (Tables 3 and 4). In the PHKS and CHKS groups, although urinary K, Na and Cl excretion, and plasma K, Na, and Cl concentration fluctuated throughout the CHK and PHK periods, they never reverted to the values observed in the UACS group (Tables 3 and 4).

URINARY

FECAL

AND PLASMA ELECTROLYTES

Urinary K, Na, and Cl excretion, as well as plasma K, Na, and Cl concentration did not change significantly in the UACS group when compared with the baseline control values (Tables 3 and 4). In the CHKS and PHKS groups, urinary electrolyte excretion and plasma electrolyte concentration increased significantly (p ⱕ 0.01) when compared with the UACS group (Tables 3 and 4). However, urinary and plasma electrolyte changes were much greater in the PHKS group than in the CHKS group. Between the PHKS and CHKS groups, no significant differCLINICAL BIOCHEMISTRY, VOLUME 33, FEBRUARY 2000

POTASSIUM

Fecal K excretion did not change significantly in the UACS group when compared with the baseline control values (Table 3). In the PHKS and CHKS groups, fecal K excretion increased significantly (p ⱕ 0.01) when compared with the UACS group (Table 3). However, fecal K excretion was much greater in the PHKS group than in the CHKS group. There were no significant differences observed between the PHKS and CHKS groups regarding the intensity of fecal K excretion. Maximum fecal K excretion always corresponded to the 41

ZORBAS

TABLE 4 Plasma Electrolyte Concentration of Athletes During Prolonged Periodic and Continuous Hypokinesia (Mean ⫾ SD)

ET AL.

TABLE 5 Plasma Renin Activity and Plasma Aldosterone Concentration in Athletes During Prolonged Periodic and Continuous Hypokinesia (Mean ⫾ SD)

Plasma concentration of electrolytes Testing days

Potassium (mEq/L)

Sodium (mEq/L)

Chloride (mEq/L)

Plasma concentration of hormones Testing days

Plasma renin activity (ng/mL/h)

Plasma aldosterone (pg/mL)

Unrestricted ambulatory control subjects, n ⫽ 10 Baseline 4.38 ⫾ 0.11 140 ⫾ 0.4 98.3 ⫾ 0.4 60th 4.40 ⫾ 0.12 142 ⫾ 0.5 99.8 ⫾ 0.6 120th 4.38 ⫾ 0.14 140 ⫾ 0.3 98.3 ⫾ 0.5 180th 4.40 ⫾ 0.12 142 ⫾ 0.6 99.9 ⫾ 0.7 240th 4.37 ⫾ 0.15 141 ⫾ 0.4 98.0 ⫾ 0.4 300th 4.39 ⫾ 0.12 139 ⫾ 0.7 96.8 ⫾ 0.5 364th 4.38 ⫾ 0.14 141 ⫾ 0.5 99.7 ⫾ 0.4 Continuous hypokinetic subjects, n ⫽ 10 Baseline 4.40 ⫾ 0.13 138 ⫾ 0.7 96.6 ⫾ 0.5 60th 4.81 ⫾ 0.4* 146 ⫾ 0.6* 105.8 ⫾ 0.8* 120th 4.73 ⫾ 0.6* 143 ⫾ 0.5* 103.3 ⫾ 0.5* 180th 5.23 ⫾ 0.8* 149 ⫾ 0.7* 109.6 ⫾ 0.6* 240th 5.01 ⫾ 0.5* 147 ⫾ 0.5* 107.8 ⫾ 0.7* 300th 5.35 ⫾ 0.6* 150 ⫾ 0.6* 110.6 ⫾ 0.9* 364th 5.24 ⫾ 0.7* 148 ⫾ 0.4* 107.7 ⫾ 0.5* Periodic hypokinetic subjects, n ⫽ 10 Baseline 4.38 ⫾ 0.11 140 ⫾ 0.5 96.0 ⫾ 0.6 60th 4.95 ⫾ 0.5* 149 ⫾ 0.6* 108.7 ⫾ 0.5* 120th 4.75 ⫾ 0.8* 146 ⫾ 0.8* 104.8 ⫾ 0.6* 180th 5.35 ⫾ 0.4* 151 ⫾ 0.6* 110.1 ⫾ 0.5* 240th 5.15 ⫾ 0.7* 148 ⫾ 0.9* 108.7 ⫾ 0.7* 300th 5.53 ⫾ 0.9* 154 ⫾ 0.7* 114.2 ⫾ 0.6* 364th 5.35 ⫾ 0.7* 149 ⫾ 0.6* 111.6 ⫾ 0.8*

Unrestricted ambulatory control subjects, n ⫽ 10 Baseline 2.25 ⫾ 0.31 46.0 ⫾ 3.3 60th 2.22 ⫾ 0.44 43.1 ⫾ 5.0 120th 2.27 ⫾ 0.53 40.4 ⫾ 6.4 180th 2.23 ⫾ 0.40 43.9 ⫾ 4.7 240th 2.27 ⫾ 0.33 40.2 ⫾ 5.4 300th 2.20 ⫾ 0.45 45.1 ⫾ 4.0 364th 2.25 ⫾ 0.51 40.3 ⫾ 6.5 Continuous hypokinetic subjects, n ⫽ 10 Baseline 2.23 ⫾ 0.42 43.4 ⫾ 5.5 60th 2.90 ⫾ 0.64* 55.9 ⫾ 4.6* 120th 2.40 ⫾ 0.45* 39.7 ⫾ 5.5* 180th 3.69 ⫾ 0.39* 75.4 ⫾ 3.8* 240th 3.15 ⫾ 0.57* 48.5 ⫾ 6.0* 300th 4.36 ⫾ 0.42* 86.0 ⫾ 5.4* 364th 4.07 ⫾ 0.60* 78.4 ⫾ 6.6* Periodic hypokinetic subjects, n ⫽ 10 Baseline 2.27 ⫾ 0.51 47.0 ⫾ 4.0 60th 3.16 ⫾ 0.60* 65.4 ⫾ 5.5* 120th 2.65 ⫾ 0.45* 57.1 ⫾ 6.0* 180th 3.92 ⫾ 0.57* 92.0 ⫾ 4.7* 240th 3.35 ⫾ 0.61* 83.3 ⫾ 5.0* 300th 5.42 ⫾ 0.44* 108.5 ⫾ 6.5* 364th 4.67 ⫾ 0.53* 94.1 ⫾ 4.6*

Significant differences (*p ⱕ 0.01) between ambulatory control and hypokinetic groups of subjects. Significant differences (†p ⱕ 0.01) between continuous and periodic hypokinetic groups of subjects.

Significant differences (*p ⱕ 0.01) between ambulatory control and hypokinetic groups of subjects. Significant differences (†p ⱕ 0.01) between continuous and periodic hypokinetic groups of subjects.

maximum plasma K concentration. During the CHK and PHK periods, fecal K excretion increased progressively while showing a pattern of a wavelike changes. In the PHKS and CHKS groups, although fecal K excretion fluctuated throughout the CHK and PHK periods, fecal K loss never reverted to the values observed in the UACS group (Table 3). PLASMA

HORMONES

PRA and PA concentration remained stable in the UACS group when compared with the baseline control values (Table 5). In the PHKS and CHKS groups, PRA and PA concentration increased significantly (p ⱕ 0.01) when compared with the UACS group (Table 5). However, plasma renin activity and PA concentration increased much more in the PHKS group than in the CHKS group. No significant differences were observed between the PHKS and CHKS groups regarding the intensity of PRA and PA concentration. In the PHKS and CHKS groups, PRA and PA concentration increased progressively while showing a pattern of a wave-like changes (Table 5). Although PRA and PA concentrations in the PHKS and CHKS groups 42

fluctuated throughout the CHK and PHK periods, they never reverted to the values observed in the UACS group (Table 5). Discussion HYPOKINETIC

REACTIONS

Because none of the hypokinetic subjects complained of any severe discomfort or any serious disorders, it may be assumed that the hypokinetic subjects tolerated well all experimental procedures. Because all signs and symptoms in hypokinetic subjects disappeared spontaneously as the duration of the HK period increased, they may be characterized as adaptational in nature. It may be assumed therefore that the observed fecal, urinary, and plasma electrolyte changes and plasma hormonal changes on the CHKS and PHKS groups could not have been caused by either severe discomfort or serious disorders following exposure to PHK and CHK. ANTHROPOMETRIC

CHANGES

Because all continuous hypokinetic subjects ended the study having lost significant amounts of CLINICAL BIOCHEMISTRY, VOLUME 33, FEBRUARY 2000

POTASSIUM CHANGES DURING PERIODIC HYPOKINESIA

their body weight, it may be assumed that they were not in energy balance but in a catabolic condition that could definitely have influenced plasma, urinary, and fecal K significantly. Body weight losses during prolonged CHK may be attributable to several factors and primarily to the prevalence of catabolic processes over anabolic processes (11–14). Meanwhile, available data (11–14) have shown that prolonged CHK is a condition of induction of catabolism characterized by a significant increase in excretion of end products, negative nitrogen balance, and a significant decrease in absolute protein tissue concentration. Unfortunately, no determination has yet been made on the actual mechanisms responsible for the significant body weight losses during prolonged CHK. It was assumed, however, that body weight losses cannot be reversed during prolonged CHK unless muscular activity is restored (13). A number of facts form an indirect proof of this hypothesis. For instance, a higher calorie intake diet and the intake of anabolic hormones do not lead to restoration of body weight during prolonged CHK. Body weight begins to recover only after the hypokinetic subjects have resumed their muscular activity. Body weight gains in the PHKS group may be attributable to several factors, while the additive effect of PHK and changes in energy metabolism should be considered first (7,8). Because the periodic hypokinetic subjects ended the study having gained significant body weight, it may be assumed that they were in an anabolic condition. However, the actual mechanism responsible for the body weight gains during prolonged PHK remained undetermined. Body fat losses in the CHKS group may be attributable to a significant mobilization of lipids from fat depots and increased lipolytic activity of fatty tissues (15–18). A significant decrease in both lipid reserves and tissues total lipids concentration has been shown during prolonged HK (15–18). This reaction of lipolitic activity could not but have contributed to the significant body fat losses in the CHKS group. The decreased fat-free body mass in the CHKS group may be attributable to the muscle wasting that is inherent to prolonged HK (19 –22). A large proportion of the fat-free body mass loss would have been a consequence of atrophy of skeletal muscle mass. The possible reasons for the body fat gains during prolonged PHK are much more complicated than the reasons for the body fat losses during prolonged CHK. However, it was assumed that body fat gains during prolonged PHK may be attributable to several factors: for instance, activation of the lipogenetic processes and inhibition of lipolytic processes, increased lipid reserves, and total lipid concentration (15–18). In the PHKS group, body fat gains may be attributable to activation of lipogenic processes and inhibition of lipolytic processes (23). A significant decrease in phospholipid concentration of the microsomal fraction of muscle suggests that during prolonged PHK changes in membrane properties CLINICAL BIOCHEMISTRY, VOLUME 33, FEBRUARY 2000

may be occurring. Increased fat free body mass in the PHKS group may be attributable to the decreased muscle wasting inherent in periodic HK. PEAK

OXYGEN UPTAKE

Decreased peak oxygen uptakes in the PHKS and CHKS groups may be associated with several factors and primarily with the deficiency of heme proteins that is inherent to prolonged HK (24 –27). It was shown that during prolonged HK, the synthesis of haemoglobin and myoglobin is decreased significantly, which then leads to heme protein deficiency (24 –27). Although heme proteins were not measured in this investigation, heme protein deficiency could have been present in this study that could definitely have influenced significantly the oxygen carrying capacity to transport oxygen in blood and muscles of the hypokinetic subjects. Consequently, the decreased peak oxygen uptake in the hypokinetic subjects may be attributable to the deficiency of heme proteins and, thus, to the decreased carrying capacity of blood to transport oxygen. A decrease in peak oxygen uptake of the hypokinetic subjects may also be attributable to the loss of muscle mass, primarily skeletal muscle mass. A further contribution to the decrease in peak oxygen uptake is the hypokinetic-induced decrease in mitochondrial density, reduced size and number of mitochondria, in skeletal muscle which may also be accompanied by a decrease in the number of capillaries around each muscle fiber, especially type 1 fibers. This is a well known and widely reported response of athletes to prolonged HK. Another explanation for the significant decrease of peak oxygen uptake is the possibility that the participants during prolonged HK may have experienced decreased motivation for training, because it is known that the level of motivation for performing any type of physical exercises during prolonged HK is significantly decreased (28,29). URINARY,

FECAL, AND PLASMA POTASSIUM

It is known when endurance trained athletes receive large amounts of electrolytes, serum or plasma electrolyte concentration does not increase significantly because much more electrolytes are deposited in different organs and systems of the body; this reaction in turn protects systemic circulation from an accelerated and a significant increase of plasma or serum electrolyte concentration by playing the role of a buffer system (1–3). However, when endurance-trained athletes are submitted to prolonged HK and large amounts of electrolytes supplements are given, serum or plasma electrolyte concentration increases significantly, leading to significant fecal and urinary electrolyte losses and, thus, to negative electrolyte balance and decreased total electrolyte concentration of the body. It was assumed therefore that decreased muscular activity is much less favorable for the deposition of electro43

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lytes in the body (1–3) than increased muscular activity. Because plasma K concentration increased significantly during CHK and PHK, it may be assumed that increased fecal and urinary K excretion in the CHKS and PHKS groups may be attributable to the decreased ability of the body to retain K (1– 6). Plasma, fecal, and urinary K changes were much greater in the PHKS group than in the CHKS group, probably due to the type of restriction of muscular activity to which the athletes were subjected, plus the additive effect of PHK. As was shown in previous studies (1–3), serum or plasma electrolyte concentration increased significantly because far fewer electrolytes could be deposited by the body, resulting in a significant fecal and urinary electrolyte excretion and, thus, in a significant negative electrolyte balance and a decrease of total electrolyte concentration of the body (1–3). Decreased ability of the body to accumulate electrolytes during prolonged CHK and PHK may be attributable to several factors: for instance, changes in bones, muscles, and cells of many tissues, where most electrolytes are deposited, impaired size of electrolyte pool of cells, and consequent change in total electrolyte concentration of cells, decreased assimilation and utilization of electrolytes for synthetic processes, injury of skeletal muscle cells that change the integrity of sarcolemma and leads to the release of intracellular electrolytes into plasma or serum, and several other factors inherent to prolonged HK (1–3). Determination of the causes of the body’s inability to retain electrolytes during prolonged HK studies was done using electrolyte loading tests. During these studies, electrolyte loading tests were administered in supplemented and unsupplemented hypokinetic groups of athletes (1– 6). It was found that the supplemented hypokinetic subjects showed a much greater and a much faster fecal and urinary electrolyte excretion than the unsupplemented hypokinetic subjects, despite the presence of a significant negative electrolyte balance and decreased total electrolyte concentration of the body. The results obtained from electrolyte loading tests also showed that the more electrolyte supplements the hypokinetic subjects receive, the more deficiency there is and the more efficient electrolytes are cleared from the blood stream. This reaction could not but have made less likely for the large intake of electrolytes to benefit the hypokinetic subjects and prevent negative electrolyte balance and increased total electrolyte concentration of the body during prolonged HK. This reaction resembles a vicious circle, that is, the higher the electrolyte intake, the greater the electrolyte losses in urine and feces and the greater the negative electrolyte balance and the decreased total electrolyte concentration of the body in the hypokinetic subjects. The failure to increase total electrolyte concentration of the body of the hypokinetic subjects and prevent negative electrolyte using electrolyte loads made it possible to formulate the following hypothesis: negative electrolyte balance and 44

ET AL.

decreased total electrolyte concentration of the body during prolonged HK is not so much a matter of electrolyte shortage in the diet as the impossibility of the body to retain electrolytes due to several reasons inherent to prolonged HK (1– 6). It is known that K is one element necessary for protein synthesis. However, during prolonged HK, total K concentration of the body is decreased significantly, which in turn leads to the significant decrease of protein synthesis. Thus, the decreased total K concentration of the body may be attributable to decreased protein synthesis, because protein synthesis is significantly decreased during prolonged HK, resulting to protein deficiency (11–14). The shortage and imbalance of proteins may affect K metabolism; however, most probably, the impossibility of the body to retain K is the primary cause of an even lower assimilation and utilization of K by the body: decreased uptake of K on the one hand and increased urinary and fecal excretion of K on the other. Then, the reaction apparently develops like a vicious circle, due to which an even greater shortage and imbalance of K occurred during prolonged HK. The failure to prevent negative K balance and increase total K concentration of the body by means of K supplements, as has been shown in previous studies (1– 6), may be seen as confirmation of this hypothesis. A significant excretion of electrolytes in urine and feces of the PHKS and CHKS groups may be associated with the significant increase of PRA and PA concentration. However, no relationship was present between the significant loss of Na and Cl from the body and the significant increase of plasma hormone concentration. A relationship was present between increased PRA and PA concentration and increased urinary and fecal K excretion in the hypokinetic subjects, and this could explain in part the significant urinary and fecal K excretion in the PHKS and CHKS groups. However, one must not associate the increased secretion of a hormone with changes in electrolyte metabolism whose balance it regulates. This reaction perhaps occurs due to the presence of several backup mechanisms and many other factors that electrolytes respond to hormonal changes during prolonged HK. Activation of a hormone does not determine the intensity of the reaction of an effector organ, because many modulators of the hormonal effect may be present while a significant and prolonged increase in hormonal activity may sometimes be sufficient to play any significant part in the regulation of electrolyte metabolism during prolonged HK. Evidently, prolonged PHK induces a much greater fecal and urinary K excretion than CHK, and against the background of a significant plasma K concentration. The cause of this type of reaction may be attributable to several factors and primarily to the regime of restriction of muscular activity, that is, PHK versus CHK. Moreover, the additive effect of PHK may have played a significant part in the rapidity and intensity of this reaction. Perhaps it is this reason for which PHK exerted a much greater effect on plasma, urinary, and fecal K values than CLINICAL BIOCHEMISTRY, VOLUME 33, FEBRUARY 2000

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CHK. All trained subjects responded to PHK with much greater plasma, urinary, and fecal K changes than to CHK. Because the PHKS group showed much greater plasma, urinary, and fecal K changes than CHKS group, it may be assumed that when endurance-trained athletes are submitted to PHK may have a much lower electrolyte stability than when they are subjected to CHK. Probably, endurance-trained athletes have a much more labile and much less responsive electrolyte metabolic control system when they are subjected to PHK versus CHK. The reasons for this reaction remain unclear. However, evidence is emerging to suggest that when endurance-trained athletes are submitted to PHK may have a much lower retention capacity for electrolytes, than when they are subjected to CHK. This reaction shows that electrolyte metabolism may be affected much more in individuals whose muscular activity is alternated for various reasons than in individuals whose muscular activity is maintained stable. Conclusions It was shown that prolonged PHK and CHK induce a significant increase of K excretion in urine and feces against the background of a significant plasma K concentration. However, plasma, fecal, and urinary K changes were much greater in the PHKS group than in the CHKS group. Differences between the PHKS and CHKS groups regarding the intensity of plasma, fecal, and urinary K changes may be attributable to several factors and primarily to the type of HK to which athletes were submitted plus the additive effect of PHK. Significant plasma, fecal, and urinary K changes in the PHKS and CHKS groups may be associated with the decreased ability of the body to retain K due to changes in muscles and cells of many tissues where most K is deposited. Unfortunately, the actual mechanisms responsible for the much greater plasma, fecal, and urinary K changes during prolonged PHK than CHK remain unclear. Understanding of the mechanisms responsible for the differences between the PHKS and CHKS groups regarding the intensity of plasma, fecal and urinary K changes might come by studying K metabolism under different forms of HK and in different individuals. Investigating metabolic electrolyte changes that might be present in individuals who are subjected to prolonged PHK due to sedentary living and working conditions may contribute to the further understanding of plasma, urinary, and fecal K changes during PHK. For the present time, it may be concluded that the greater the stability of muscular activity, the smaller the K changes in plasma, urine, and feces during prolonged HK. Unfortunately, the actual mechanism by which plasma, urinary, and fecal K was affected much more during PHC than CHK could not be established and requires further study. However, this reaction must be taken into account when one is dealing with people CLINICAL BIOCHEMISTRY, VOLUME 33, FEBRUARY 2000

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