Eur J Appl Physiol (1992) 65:331-334
European
ou,o, A p p l i e d Physiology and Occupational Physiology © Spnnger-Verlag 1992
Active and inactive renin after exercise M. Ikeda 1, M. Matsusaki ~, A. Kinoshita ~, M. Koga 1, M. Ideishi ~, M. Sasaguri ~, H. Tanaka 2, M. Shindo 2, and K. Arakawa ~ 1 Department of Internal Medicine, Fukuoka University School of Medicine, 7-45-1 Nanakuma, Jonan-ku, Fukuoka 814-01, Japan z Department of Exercise Physiology, School of Physical Education, Fukuoka University, 7-45-1 Nanakuma, Jonanku, Fukuoka 814-01, Japan Accepted May 14, 1992
Summary. The effects of graded exercise on plasma concentrations of active and inactive renin were studied in seven healthy men. Exercise was performed on a cycle ergometer at four different exercise intensities (corresponding to 30%, 50o/0, 80o/0 and 87% of DrO2max)for 10 min each. Concentrations of active renin and total renin after activation by trypsin were measured by direct immunoradiometric assay. Non-trypsin-activated renin concentration (inactive) was obtained by subtraction. Active renin concentrations at 30%, 50%, 80% and 87% of 1202max were 1.2, 1.9, 3.1 and 4.6 times higher than the control concentration, respectively. Similar increases in plasma renin concentration, determined by conventional enzymatic assay, were observed at every stage. In contrast, changes in inactive renin concentration were not significant at any stage. Significant increases in noradrenaline concentration were found at every exercise stage, but adrenaline, aldosterone and lactate concentrations were significantly elevated only after exercise at 50%, 80% and 87% of 1202 . . . . The similarity between the changes in concentration of active renin and noradrenaline would suggest that sympathetic nerve activity m a y have been responsible either for the release of active renin or for the conversion of inactive renin to its active f o r m in the kidney.
Key words: Active renin - Inactive renin - Lactate threshold - Noradrenaline
Renin release is stimulated by excitation of the sympathetic adrenergic nervous system and by decreased renal blood flow or blood volume (Kotchen et al. 1971; W o l f et al. 1986; Zambraski et al. 1984). There are active and inactive forms of renin in the circulation (Derkx et al. 1976; Leckie et al. 1977; Boyd 1977) and it has recently been suggested that there are two pathways for renin secretion f r o m the kidney, a constitutive pathway and a regulated pathway (Galen et al. 1984; Pratt et al. 1987, 1988). The constitutive pathway is considered to be responsible for the secretion of newly synthesized prorenin or inactive renin by an unregulated mechanism. In contrast, in the regulated pathway, renin is secreted f r o m the renin storage granules by an isoproterenol-sensitive mechanism (Hsueh et al. 1985; Misbin and Pecker 1987). However, it is still not known whether the increase in plasma renin activity is due to increased release of active renin, or to increased conversion of inactive renin to active renin in the kidney or in the circulation. The purpose of the present study was to assess the influence of different exercise intensities on the plasma concentrations of active and inactive forms of renin in relation to sympathetic nerve activity.
Methods Subjects. Seven healthy active young male volunteers (mean age
Introduction It has been reported that exercise is associated with an increase in plasma renin activity, and that this increase is proportional to exercise intensity or heart rate, or both (Kotchen et al. 1971; Fujita et al. 1982; Guezennec et al. 1986; W o l f et al. 1986).
Correspondence to: M. Ikeda
22.9 years) were studied. Consent was obtained from all the subjects after they were informed of the nature and purpose of the study. Their physical characteristics are summarized in Table 1. Exercise. Before the investigation, they underwent multistage sub-
maximal graded exercise testing on an electric cycle ergometer to determine exercise capacity. The exercise tests were conducted in an air conditioned room. The exercise intensity was increased by 20 W every 2 rain and blood samples were obtained from an earlobe just before the end of each stage. Blood lactate was measured with a Roche 640 lactate analyser. The blood lactate values were plotted against the intensity of exercise and intensities corresponding to the blood lactate threshold, above which blood lactate began to increase abruptly, and the 4 mmol'1-1 level of blood lactate, were determined. The exercise intensity at the blood lactate
332 Table 1. Characteristics of subjects (n = 7)
Variables
Mean
SEM
Age (years) Height (cm) Body mass (kg) [?O2max'mass - l ( m l . k g - l . m i n -1)
22.9 170.3 63.3 48.3
0.5 2.2 2.6 1.7
Active renin concentration was measured by immunoradiometric assay as previously reported (Ikeda et al. 1991). Total renin concentration was measured by immunoradiornetric assay after activation by trypsin at 25 ° C for 10 min (Sealey et al. 1980). Inactive renin was calculated by subtracting the active renin concentration from the total renin concentration. The PRA was measured according to Ogihara et al. (1977) by radio-immunoassay using a commercial kit (Dainabot, Tokyo, Japan) and plasma aldosterone concentration was measured according to Ikeda et al. (1981) by radio-immunoassay using a commercial kit (Dalnabot, Tokyo, Japan). Plasma noradrenaline and adrenaline concentrations were measured by the trihydroxyindole method (Merrills 1962) after separation and extraction by high performance liquid chromatography.
threshold occurred at approximately 40-60% of the maximal oxygen uptake (1202m~) [Tanaka et al. 1986; Urata et al. 1987]. After determination of exercise intensities at the blood lactate threshold and the 4 mmol-1 -1 level of blood lactate, four different exercise intensities were established as follows: stage 1 - half the intensity at the blood lactate threshold, corresponding to 30.4% oxygen uptake (12Ozm~x); stage 2 - the intensity at the blood lactate threshold, corresponding to 50.2% 1202rnax; stage 3 - the intensity at 4 m m o l . l - 1 of blood lactate, corresponding to 79.8% I?O2m~; and stage 4 - a medium intensity between stage 3 and the maximum intensity corresponding to 87.0% l?O2m~ (Tanaka et al. 1986). After an overnight fast, the subjects were weighed and cannulae were inserted into forearm veins for blood sampling. The 1202, heart rate, and blood pressure were measured after 30 min sitting in a chair as a control. Graded exercise was performed on the cycle ergometer at the four stages for 10 rain at each stage. During the last minute at each stage, I;'O2, heart rate, and blood pressure were measured. Capillary blood from an earlobe for lactate measurement and venous blood were obtained during the last 2 min at each stage.
Statistical analysis. Wilcoxon signed rank tests were used to evaluate differences between rest and exercise. Statistically significant differences were set at the 0.05 level of confidence.
Results
The changes in physical and hormonal parameters are summarized in Tables 2 and 3. Percentage changes in concentrations of active renin, inactive renin and noradrenaline, and % 1702, are illustrated in Fig. 1. Active renin concentrations were significantly greater than the control value at every exercise stage. Active renin concentrations after exercise at 30%, 50%, 80% of and 87% of 1?Ozmaxwere 1.2, 1.9, 3.2 and 4.6 times the control level, respectively (Fig. 1, upper left). Similar increases in PRA were observed at every stage. However, inactive renin concentrations did not differ from the control values at any stage (Fig. 1, upper right). The ratio of active to inactive renin concentration
Measurement. Capillary blood was used for lactate analysis. Blood obtained from the canulated antecubital vein was analysed for active renin, total renin, plasma renin activity (PRA), noradrenaline, adrenaline and aldosterone concentrations. Blood was also collected and analysed 15 min after the end of exercise.
Table 2. Changes of physical parameters during graded exercise (n = 7)
Parameter
Rest
Stage 1
Exercise intensity (W) 1202 ( m l ' m i n - l " k g -1) % 1202 Heart rate (beats'min -~) BPs (kPa) BPd (kPa) Blood lactate concentration (mmol'l -~)
mean -4.7 9.8 63.4 15.61 9.51 1.29
SEM 0.2 1.8 0.69 0.68 0.16
mean 51.7 14.6 30.4 89.0 17.69 9.15 1.48
Stage 2 SEM 4.4 1.0' 4.1" 0.95* 0.79 0.19
mean 102.9 24.1 50.2 124.1 21.33 10.19 2.96
Stage 3 SEM 9.1 2.4* 6.6* 0.87* 0.93 0.42*
mean 149.9 38.3 79.8 167.4 24.77 8.89 4.97
Stage 4 SEM 9.1 3.3* 1.8" 1.97" 0.76 0.41"
mean 184.3 41.8 87.0 175.7 22.76 8.48 8.64
Recovery SEM 6.9 1.3"
mean
SEM
8.3* 3.17" 0.84 0.65*
98.7 15.95 10.05 6.24
3.4* 0.44* 0.64 1.06'
1202, Oxygen uptake; BPs, systolic blood pressure; BPd, diastolic blood pressure; * P < 0.05, compared to rest
Table 3. Changes in hormonel concentration during graded exercise (n = 7)
Hormone
Rest
PRA ( n g . m l - l . h -1) Active renin (pg.m1-1) Total renin (pg'm1-1) Inactive renin (pg.ml -~) Active:inactive renin ratio Aldosterone (pg-m1-1) Noradrenaline (ng'ml -a) Adrenaline (ng.ml-1)
mean 1.4 18.2 117.1 98.8 0.25 119 0.15 0.02
Stage 1 SEM 0.3 2.4 12.6 13.1 0.09 16 0.01 0.00
mean 2.0 22.1 126.8 104.7 0.27 118 0.28 0.02
Stage 2 SEM 0.3* 2.1' 13.4" 14.3 0.08 17 0.05* 0.00
PRA, Plasma renin activity; * P
European
ou,o, A p p l i e d Physiology and Occupational Physiology © Spnnger-Verlag 1992
Active and inactive renin after exercise M. Ikeda 1, M. Matsusaki ~, A. Kinoshita ~, M. Koga 1, M. Ideishi ~, M. Sasaguri ~, H. Tanaka 2, M. Shindo 2, and K. Arakawa ~ 1 Department of Internal Medicine, Fukuoka University School of Medicine, 7-45-1 Nanakuma, Jonan-ku, Fukuoka 814-01, Japan z Department of Exercise Physiology, School of Physical Education, Fukuoka University, 7-45-1 Nanakuma, Jonanku, Fukuoka 814-01, Japan Accepted May 14, 1992
Summary. The effects of graded exercise on plasma concentrations of active and inactive renin were studied in seven healthy men. Exercise was performed on a cycle ergometer at four different exercise intensities (corresponding to 30%, 50o/0, 80o/0 and 87% of DrO2max)for 10 min each. Concentrations of active renin and total renin after activation by trypsin were measured by direct immunoradiometric assay. Non-trypsin-activated renin concentration (inactive) was obtained by subtraction. Active renin concentrations at 30%, 50%, 80% and 87% of 1202max were 1.2, 1.9, 3.1 and 4.6 times higher than the control concentration, respectively. Similar increases in plasma renin concentration, determined by conventional enzymatic assay, were observed at every stage. In contrast, changes in inactive renin concentration were not significant at any stage. Significant increases in noradrenaline concentration were found at every exercise stage, but adrenaline, aldosterone and lactate concentrations were significantly elevated only after exercise at 50%, 80% and 87% of 1202 . . . . The similarity between the changes in concentration of active renin and noradrenaline would suggest that sympathetic nerve activity m a y have been responsible either for the release of active renin or for the conversion of inactive renin to its active f o r m in the kidney.
Key words: Active renin - Inactive renin - Lactate threshold - Noradrenaline
Renin release is stimulated by excitation of the sympathetic adrenergic nervous system and by decreased renal blood flow or blood volume (Kotchen et al. 1971; W o l f et al. 1986; Zambraski et al. 1984). There are active and inactive forms of renin in the circulation (Derkx et al. 1976; Leckie et al. 1977; Boyd 1977) and it has recently been suggested that there are two pathways for renin secretion f r o m the kidney, a constitutive pathway and a regulated pathway (Galen et al. 1984; Pratt et al. 1987, 1988). The constitutive pathway is considered to be responsible for the secretion of newly synthesized prorenin or inactive renin by an unregulated mechanism. In contrast, in the regulated pathway, renin is secreted f r o m the renin storage granules by an isoproterenol-sensitive mechanism (Hsueh et al. 1985; Misbin and Pecker 1987). However, it is still not known whether the increase in plasma renin activity is due to increased release of active renin, or to increased conversion of inactive renin to active renin in the kidney or in the circulation. The purpose of the present study was to assess the influence of different exercise intensities on the plasma concentrations of active and inactive forms of renin in relation to sympathetic nerve activity.
Methods Subjects. Seven healthy active young male volunteers (mean age
Introduction It has been reported that exercise is associated with an increase in plasma renin activity, and that this increase is proportional to exercise intensity or heart rate, or both (Kotchen et al. 1971; Fujita et al. 1982; Guezennec et al. 1986; W o l f et al. 1986).
Correspondence to: M. Ikeda
22.9 years) were studied. Consent was obtained from all the subjects after they were informed of the nature and purpose of the study. Their physical characteristics are summarized in Table 1. Exercise. Before the investigation, they underwent multistage sub-
maximal graded exercise testing on an electric cycle ergometer to determine exercise capacity. The exercise tests were conducted in an air conditioned room. The exercise intensity was increased by 20 W every 2 rain and blood samples were obtained from an earlobe just before the end of each stage. Blood lactate was measured with a Roche 640 lactate analyser. The blood lactate values were plotted against the intensity of exercise and intensities corresponding to the blood lactate threshold, above which blood lactate began to increase abruptly, and the 4 mmol'1-1 level of blood lactate, were determined. The exercise intensity at the blood lactate
332 Table 1. Characteristics of subjects (n = 7)
Variables
Mean
SEM
Age (years) Height (cm) Body mass (kg) [?O2max'mass - l ( m l . k g - l . m i n -1)
22.9 170.3 63.3 48.3
0.5 2.2 2.6 1.7
Active renin concentration was measured by immunoradiometric assay as previously reported (Ikeda et al. 1991). Total renin concentration was measured by immunoradiornetric assay after activation by trypsin at 25 ° C for 10 min (Sealey et al. 1980). Inactive renin was calculated by subtracting the active renin concentration from the total renin concentration. The PRA was measured according to Ogihara et al. (1977) by radio-immunoassay using a commercial kit (Dainabot, Tokyo, Japan) and plasma aldosterone concentration was measured according to Ikeda et al. (1981) by radio-immunoassay using a commercial kit (Dalnabot, Tokyo, Japan). Plasma noradrenaline and adrenaline concentrations were measured by the trihydroxyindole method (Merrills 1962) after separation and extraction by high performance liquid chromatography.
threshold occurred at approximately 40-60% of the maximal oxygen uptake (1202m~) [Tanaka et al. 1986; Urata et al. 1987]. After determination of exercise intensities at the blood lactate threshold and the 4 mmol-1 -1 level of blood lactate, four different exercise intensities were established as follows: stage 1 - half the intensity at the blood lactate threshold, corresponding to 30.4% oxygen uptake (12Ozm~x); stage 2 - the intensity at the blood lactate threshold, corresponding to 50.2% 1202rnax; stage 3 - the intensity at 4 m m o l . l - 1 of blood lactate, corresponding to 79.8% I?O2m~; and stage 4 - a medium intensity between stage 3 and the maximum intensity corresponding to 87.0% l?O2m~ (Tanaka et al. 1986). After an overnight fast, the subjects were weighed and cannulae were inserted into forearm veins for blood sampling. The 1202, heart rate, and blood pressure were measured after 30 min sitting in a chair as a control. Graded exercise was performed on the cycle ergometer at the four stages for 10 rain at each stage. During the last minute at each stage, I;'O2, heart rate, and blood pressure were measured. Capillary blood from an earlobe for lactate measurement and venous blood were obtained during the last 2 min at each stage.
Statistical analysis. Wilcoxon signed rank tests were used to evaluate differences between rest and exercise. Statistically significant differences were set at the 0.05 level of confidence.
Results
The changes in physical and hormonal parameters are summarized in Tables 2 and 3. Percentage changes in concentrations of active renin, inactive renin and noradrenaline, and % 1702, are illustrated in Fig. 1. Active renin concentrations were significantly greater than the control value at every exercise stage. Active renin concentrations after exercise at 30%, 50%, 80% of and 87% of 1?Ozmaxwere 1.2, 1.9, 3.2 and 4.6 times the control level, respectively (Fig. 1, upper left). Similar increases in PRA were observed at every stage. However, inactive renin concentrations did not differ from the control values at any stage (Fig. 1, upper right). The ratio of active to inactive renin concentration
Measurement. Capillary blood was used for lactate analysis. Blood obtained from the canulated antecubital vein was analysed for active renin, total renin, plasma renin activity (PRA), noradrenaline, adrenaline and aldosterone concentrations. Blood was also collected and analysed 15 min after the end of exercise.
Table 2. Changes of physical parameters during graded exercise (n = 7)
Parameter
Rest
Stage 1
Exercise intensity (W) 1202 ( m l ' m i n - l " k g -1) % 1202 Heart rate (beats'min -~) BPs (kPa) BPd (kPa) Blood lactate concentration (mmol'l -~)
mean -4.7 9.8 63.4 15.61 9.51 1.29
SEM 0.2 1.8 0.69 0.68 0.16
mean 51.7 14.6 30.4 89.0 17.69 9.15 1.48
Stage 2 SEM 4.4 1.0' 4.1" 0.95* 0.79 0.19
mean 102.9 24.1 50.2 124.1 21.33 10.19 2.96
Stage 3 SEM 9.1 2.4* 6.6* 0.87* 0.93 0.42*
mean 149.9 38.3 79.8 167.4 24.77 8.89 4.97
Stage 4 SEM 9.1 3.3* 1.8" 1.97" 0.76 0.41"
mean 184.3 41.8 87.0 175.7 22.76 8.48 8.64
Recovery SEM 6.9 1.3"
mean
SEM
8.3* 3.17" 0.84 0.65*
98.7 15.95 10.05 6.24
3.4* 0.44* 0.64 1.06'
1202, Oxygen uptake; BPs, systolic blood pressure; BPd, diastolic blood pressure; * P < 0.05, compared to rest
Table 3. Changes in hormonel concentration during graded exercise (n = 7)
Hormone
Rest
PRA ( n g . m l - l . h -1) Active renin (pg.m1-1) Total renin (pg'm1-1) Inactive renin (pg.ml -~) Active:inactive renin ratio Aldosterone (pg-m1-1) Noradrenaline (ng'ml -a) Adrenaline (ng.ml-1)
mean 1.4 18.2 117.1 98.8 0.25 119 0.15 0.02
Stage 1 SEM 0.3 2.4 12.6 13.1 0.09 16 0.01 0.00
mean 2.0 22.1 126.8 104.7 0.27 118 0.28 0.02
Stage 2 SEM 0.3* 2.1' 13.4" 14.3 0.08 17 0.05* 0.00
PRA, Plasma renin activity; * P
