Clinical Science (1979) 51,3179-320s

Effect of isometric exercise on the renal excretion of sodium and potassium in mild hypertension P. S. P A R F R E Y , P. W R I G H T

A N D J. M. L E D I N G H A M Medical Clnir. The London Hospital, Whitechapel,London

Summary

1. Basal levels of pulse rate, blood pressure and rates of sodium and potassium excretion were observed in eight white male patients with mild hypertension and eight age-, sex- and colourmatched controls during an initial rest period of 90 min and then for 5 h after a 1 h period of isometric exercise involving all four limbs in rotation. The studies were repeated on another day with the subjects resting instead of exercising for 1 h. 2. Changes in systolic pressure after exercise were similar in the hypertensive and control groups, whereas the rise in diastolic pressure was higher and the rise in pulse rate lower after exercise in the hypertensive group compared with the control group. 3. The changes in the rate of salt excretion were significantly different in the two groups, the hypertensive group retaining proportionately more sodium and potassium over several hours. Key words: exercise, hypertension, potassium, sodium.

Introduction It has been suggested that deficient sodium excretion could have a primary role in the pathogenesis of all forms of hypertension (Borst & Borst, 1963), a postulate receiving strong support from the work of Guyton, Coleman, Cowley, Scheel, Manning & Norman (1972). Mental stress can induce increased and sustained circulatory changes in labile hypertensive patients and in some normotensive subjects with a genetic risk of hypertension (Falkner, Onesti, Angelakos, Fernandes & LongCorrespondence: Dr P. S. Parfrey, Medical Unit, The London Hospital, Whitechapel, London.

man, 1979). Also, patients with high blood pressure may respond to mental stress with greater renal vasoconstriction than normotensive patients (Brod, Fencl, Hejl & Jirka, 1959). However, a definite link between stess and a hypertensive mechanism in man has not been defined. The cardiovascular responses to isometric exercise are similar to but of greater magnitude than responses to mental stress (Nyberg, 1976). The purpose of this investigation was to explore the possibility that patients with mild hypertension retain excessive sodium and potassium after a period of strenuous isometric exercise. Methods

Eight white males with mild hypertension aged between 20 and 50 years were studied. In each patient, the average of eight resting diastolic blood pressure readings was greater than 90 mmHg and less than 120 mmHg, measured after If h supine rest on the 2 days of the experiment. All were attending the out-patient clinic and were untreated, newly diagnosed, essential hypertensive patients without organ damage and with no identifiable underlying cause for the hypertension. Eight sex-, colour- and age-matched healthy control subjects were also studied, whose average diastolic blood pressure, measured in a similar fashion, was less than 85 mmHg. All the control subjects had no family history of high blood pressure. Blood pressure was measured by the Arteriosonde automatic blood pressure monitor in half the 'subjects, chosen at random, and by cuff sphygmomanometry in the other half. Heart rate was counted from the radial pulse over 20 s. Urinary sodium and potassium concentrations were determined by flame photometry. ARer their usual breakfast, patients attended the

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medical investigation room at 09.00 hours and voided urine. They had been advised to abstain from tea, coffee and cigarette smoking from midnight. Urine volume was maintained by ingesting 500 ml of water each hour for the duration of the experiment. A lunch of meat, salad and trifle was eaten at 12.45 hours. Each subject rested supine until 10.30 hours. Then blood pressure (x4) and heart rate ( x 2) were measured between 10.15 and 10.30 hours, and the urine was collected by voluntary voiding to define the basal rate of sodium and potassium excretion. Subsequently blood pressure (x2), heart rate and rate of salt excretion were measured at 11.30, 12.00, 12.30, 13.00, 13.30, 14.30, 15.30 and 16.30 hours. Each subject was asked to empty his bladder completely on each occasion while standing in privacy. Between 10.30 and 11.30 hours each patient performed isometric exercise involving each limb in rotation. Sustained right-hand grip at 50% of maximal voluntary contraction was performed for 1 min, a rolled blood pressure cuff attached to a sphygmomanometer being used. Then a 30 s rest ensued, followed by sustained left-hand grip at 50% maximal contraction for 1 min. Another 30 s rest was taken, followed by elevation of the outstretched right lower limb to 45O above the horizontal for 1 min. After a 30 s rest, left lower limb elevation to 45O for 1 min was undertaken. A rest for 2 min was allowed and then the entire sequence was repeated six times for 1 h. The studies were repeated on another day with the subjects resting instead of exercising for 1 h. The circulatory response to exercise of each subject was expressed as the difference of the changes from basal values on exercise and rest days. The salt-excretion response was expressed as the ratio of the changes from the basal levels observed on the exercise and rest days. Student’s two-tailed t-test was used for statistical analysis. Results

Resling values Mean resting systolic blood pressure was 144 & SE 3.1 mmHg in the hypertensive group and 11 1 + 3.0 mmHg in the control group. The respective values for diastolic blood pressure were 97 f 2.7 mmHg and 75 _+ 1.7 mmHg; pulse rate: 75 k 3.3/min and 68 +_ 2.l/min; sodium excretion rate: 13.5 f 3.7 mmol/h and 11.5 f 2.8 mmol/h; potassium excretion rate: 5.7 _+ 1.0 mmollh and 5.1 f 1.7 mmol/h.

Cardiovascular responses to exercise (Fig. 1) Changes in systolic blood pressure after exercise were similar in the hypertensive and control groups, whereas the rise in diastolic pressure (compared with the control day) was higher and the rise in pulse rate lower in the hypertensive group compared with the control group. The difference in diastolic blood pressure response between the two groups was significant ( P < 0.05) for the first hour after exercise. Salt excretion response to exercise (Fig. 1) The hypertensive group retained proportionately more sodium and potassium than the control group for the duration of the experiment. The difference between the two groups was significant for the first hour after exercise, in the case of sodium, and for potassium the difference was significant at all times except at 3 h after exercise. Discussion

This study was designed to discover whether stress in the form of isometric exercise had a more sustained effect, after the cessation of stress, on the circulation of patients with mild essential hypertension and whether this was reflected in a similarly protracted effect on sodium and potassium excretion. Patients with high blood pressure tend to have a more reactive pressor response during isometric exercise (Ewing, Irving, Kerr & Kirby, 1973; Brorson, Wasir & Sannerstedt, 1978). A sustained pressor response to mental stress in hypertensive patients has been observed by Brod et al. (1959) and Baumann, Ziprian, Godicke, Naumann & Lauter (1973). Falkner et al. (1979) reported a sustained increase in systolic and diastolic pressures for 5 min after a 10 min period of mental arithmetic in labile hypertensive patients, a finding not observed in normal subjects. In the present investigation a sustained rise in diastolic, but not in systolic, pressure and a probable reflex decrease in pulse rate of hypertensive patients compared with matched controls was observed for the first few hours after isometric exercise. Our results also show that the hypertensive group retained proportionately more sodium and potassium than the controls for several hours after exercise. This could have been due either to excessive renal sympathetic nerve activity or to an abnormally large response of the kidney to the normal sympathetic activity associated with exercise.

Exercise and cation excretion in hypertension

1

Systolic B.P. response

3 19s

Diastolic B.P. response

24 20 16

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12 8 4

0 1

2

3

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5

-4

Time (h) after exercise -8

Sodium excretion response

2 5

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Potassium excretion response

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075 0.50

FIG.1. Blood pressure (B.P.) and salt excretion responses to 1 h of isometric exercise in hypertensive compared with normotensive control subjects (x---x). The upper two diagrams subjects (M) illustrate the systolic blood pressure (left) and diastolic blood pressure (right) responses, with the ordinate depicting the difference in the change of pressure at time t from basal values between the rest and exercise days. The lower two diagrams illustrate the sodium (left) and potassium (right) excretion responses with the ordinate derived from the ratios Salt excretiodh at ton exercise day

/ Salt excretiodh at ton rest day

Basal salt excretiodh on exercise day/ Basal salt excretiodh on rest day The abscissa in all four diagrams is the time (h) after exercise.

It is not possible to say whether the observed excessive salt retention after isometric exercise in the hypertensive patients is a consequence of the hypertension or whether it is part of a pathogenic

mechanism relevant to the development of hypertension. Protracted sodium retention could augment hypertensive processes. Further investigations are in process in young normotensive subjects,

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genetically prone to hypertension, to shed light on this problem.

Acknowledgment

We are grateful to the Medical Research Council for financial support.

References BAUMANN,R., ZIPRIAN,H., GODICKE,W., NAUMANN,E. & LAUTER,J. (1973)The influence of acute psychic stress situations on biochemical and vegetative parameters of essential hypertensives at the early stage of the disease. Psychorher. Psychosom., 22,131-140. BORST,J.G. & BORST, G.A. (1963)Hypertension explained by Starling's theory of circulatory homeostasis. Lancet, i, 677682.

BROD,J., FENCL,V., HI?& . , 2. & JIRKA, J. (1959)Circulatory changes underlying blood pressure elevation during acute emotional stress (mental arithmetic) in normotensive and hypertensive subjects. Clinical Science, 18,269-279. BRORSON,L., WAsm, H. & SANNERSIEDT,R. (1978)H m o dynamic effects of static and dynamic exercise in males with arterial hypertension of varying severity. Cardiovascular Research, 12,269-275.

EWING,D.J.,IRVING,J.B.,KERR,F.&KIRBY,BJ.(~~~~)S~~~ exercise in untreated systemic hypertension. British Hearr Journal, 35.4 13-421. FALKNER,B., ONESTI,G., ANGELAKOS, E.T., FERNANDES,M. & LONGMAN, C. (1979) Cardiovascular response to mental stress in normal adolescents with hypertensive parents. Hyprtension, I,23-30. GWTON, A.C., COLEMAN,T.G., COWLEY,A.W., SCHEEL, K.W., MANNING,R.D. & NORMAN,R.A. (1972) Arterial pressure regulation. O v k d i n g dominance of the kidneys in long-term regulation and in hypertension. American Journal of Medicine, S2,584-594. NYBERG,G. (1976)Blood pressure and heart rate respone to isometric exercise and mental arithmetic in normotensive and hypertensive subjects. Clinical Science and Molecular Medicine, 51 (Suppl. 3),6819-685s.

Effect of isometric exercise on the renal excretion of sodium and potassium in mild hypertension.

Clinical Science (1979) 51,3179-320s Effect of isometric exercise on the renal excretion of sodium and potassium in mild hypertension P. S. P A R F R...
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