Biochemical variables in plasma and urine before and after prolonged physical exercise

Nine normal young male students were studied during 2 days of relative rest, during 2 days of physical training and again during the succeeding 2 days of relative rest. 24-hour urine collections showed that the creatinine, creatine, uric acid, urea, calcium and magnesium excretion were similar during the resting and exercise days. The 24-hour urinary excretion of sodium and potassium was decreased during the exercise days, while the aldosterone excretion was increased. The hemoglobin concentration, hematocrit and red cell counts were decreased 14, as well as 42 h after exercise. The serum uric acid, creatine phosphokinase-MM (skeletal muscles) subfraction, glutamic oxalacetic transaminase and myoglobin levels were increased 14 h after exercise, but returned to baseline 42 h after this type of exercise. The mechanisms of these alterations were discussed and the data show that one should take into account previous exercise when interpreting the results of certain of these tests.     

Plasma aldosterone and renal function in runners during a 20-day road race

To evaluate the effects that repeated long-distance running has on plasma aldosterone concentration and urinary excretion of solutes, fifteen male runners were studied during a 20-day, 500-km road race. Venous blood samples were taken on day 1 prior to running, on day 11 after 10 days of running, on day 13 after a 70-h rest, and on day 18 after an additional five days of running. Overnight urine samples were obtained on day 10 before and after running and on days 11, 12, and 13 during the 70-h rest period. Plasma sodium concentrations on days 13 and 18 and plasma potassium concentrations on days 11 and 13 were decreased (P less than 0.05). Plasma aldosterone levels were increased on days 11 and 18 after running and returned to pre-race levels on day 13 after 70 h of rest. Plasma cortisol concentrations were not altered. The urinary excretion rates of sodium were elevated and of aldosterone were decreased after 70 h of rest. Increase in excretion rate of urinary sodium correlated with decrease in concentration of plasma aldosterone. These findings show that plasma aldosterone levels are chronically elevated with repeated long-distance running, resulting in a decrease in urinary excretion rate of sodium.     

Beta-adrenoceptors and the regulation of blood pressure and plasma renin during exercise

The relative role of beta 1- and beta 2-adrenoceptors in the regulation of blood pressure and plasma renin at rest and during exercise was studied in 17 normal male volunteers. They performed, in a randomized order and according to a double-blind crossover study design, three graded and uninterrupted exercise tests until exhaustion after being pretreated during 3 consecutive days with a placebo, with a predominantly beta 1-blocker (atenolol, 50 mg once/day), or with a predominantly beta 2-blocker (ICI 118551, 20 mg 3 times/day). Both drugs caused a decrease of heart rate, but the reduction by ICI 118551 was less pronounced at rest and no additional decline occurred at exercise. ICI 118551 did not affect blood pressure at rest, but during exercise diastolic blood pressure was higher than after a placebo. Atenolol lowered systolic blood pressure at rest and suppressed the exercise-induced increase in systolic blood pressure. At rest and during exercise plasma renin activity was lowered by predominantly beta 1-blockade and unchanged during beta 2-antagonism. The exercise-induced increase in plasma renin was, however, not affected by the beta 1-blocker. After atenolol the urinary excretion of aldosterone was decreased but the plasma aldosterone concentration was not changed. ICI 118551 did not alter plasma or urinary aldosterone. Our results therefore provide further evidence that the adrenoceptors mediating the release of renin at rest and during exercise in humans are partially of the beta 1-subtype, whereas beta 2-adrenergic receptors probably play only a minor role in the control of renin secretion, especially at exercise.(ABSTRACT TRUNCATED AT 250 WORDS)     

Plasma aldosterone and sweat sodium concentrations after exercise and heat acclimation

This investigation was designed to determine the relationship between the levels of plasma aldosterone and eccrine sweat gland sodium excretion following exercise and heat acclimation. Ten subjects exercised at 45% of their maximal O2 uptake in a hot (40 degrees C), moderately humid (45% relative humidity) environment for 2 h/day on ten consecutive days. Acclimation was verified by significant reductions in exercise heart rate, rectal temperature, and heat storage, as well as significant elevation of resting plasma volume (12%, P less than 0.05) and exercise sweat rate on day 10 compared with day 1 of acclimation. During exercise, the concentration and total content of sodium in sweat as well as plasma aldosterone were significantly decreased from day 1 to day 10. The ratio of sweat sodium reabsorbed to plasma aldosterone concentration was significantly increased from day 1 to day 10 after both 1 and 2 h of exercise. These data indicate that plasma aldosterone concentrations decrease following heat acclimation; and eccrine gland responsiveness to aldosterone, as represented by sweat sodium reabsorption, may be augumented through exercise and heat acclimation.     

Effects of the renin-angiotensin-aldosterone system on the cardiovascular system during 20-days bed rest

Long term change of renin-angiotensin-aldosterone system (RAAS) induced by bed rest and its effects on cardiovascular system are still controversial. The purpose of this study was to obtain a general conclusion on these questions by analyzing our two 20-days horizontal bed rest experiments in past two years with 18 subjects. Plasma renin activity and aldosterone were consistently increased during the bed rest, but angiotensin II was increased only during the early days. Decrease in urinary sodium excretion and increase in urinary potassium excretion were observed during day 3-8 and day 7-12, respectively. Mean arterial pressure increased during day 3-8. Pulse pressure was returned to pre-bed rest level by day 10 after an initial decrease. All these results indicated an activated RAAS and its active effects on cardiovascular and overall fluid regulating systems during our horizontal bed rest studies. Direct effect of change in gravitational force on renal pressure-sensitive cells or effects related to physical inactivity may explain our results.     

Influence of endogenous opioids on atrial natriuretic factor release during exercise in man

To evaluate to what extent opioid secretion in exercise induces the release of atrial natriuretic factor (ANF), six healthy male volunteers who were trained subjects, were submitted to two maximal exercise tests with and without (control) opioid receptor blockade by Naltrexone. Blood samples were drawn before (rest) and after exercise (post-exercise) in order to measure human ANF (alpha h ANF), beta-endorphin, plasma aldosterone concentration (PAC) plasma renin activity (PRA) and adreno-cortico trophic hormone (ATCH) by radio-immunological methods. Expired gas was collected during exercise to measure oxygen consumption. On average, the same maximal oxygen consumption (VO2max) during exercise was reached by all subjects with and without treatment. Plasma ANF level at rest slightly decreased after administration of Naltrexone; the response to physical exercise was significantly reduced by Naltrexone. There was no statistical difference between plasma levels of beta-endorphin, PRA and ACTH at rest nor in the post-exercise situation under the influence of Naltrexone. The PAC increased significantly at rest after Naltrexone administration but there was no statistical difference between both values after exercise. These data demonstrate that: (1) ANF secretion during exercise is influenced by the level of beta-endorphin in the plasma; (2) the possible inhibitory role of ANF on aldosterone secretion during exercise is probably over-ruled by the increase in plasma ACTH and PRA.     

Circadian variations in plasma renin activity, catecholamines and aldosterone during exercise in women

Four women were studied at 0400 h and 1600 h to determine if their hormonal and hemodynamic responses to exercise varied with the circadian cycle. Esophageal temperature was measured during rest and exercise (60% peak VO2; 30 min) in a warm room (Ta = 35 degrees C; PH2O = 1.7 kPa). Venous blood samples were drawn during rest and exercise and hemoglobin concentration (Hb), hematocrit (Hct), plasma osmolality (Posm), plasma protein concentration (Pp), colloid osmotic pressure (COP), plasma renin activity (PRA), cortisol, aldosterone, norepinephrine (NE) and epinephrine (E) were determined. Changes in plasma volume (PV) were estimated from changes in Hb and Hct. The relative hemoconcentration (-11.2%) was similar at 0400 h and 1600 h, but the absolute PV was smaller at 1600 h than at 0400 h (p = 0.03). The responses of Posm, Pp and COP to exercise were unaffected by time of day. Although PRA was not different at the two times of day, PRA was 244% greater during exercise at 1600 h, but only 103% greater during exercise at 0400 h. The normal circadian rhythms in plasma aldosterone (p = 0.043) and plasma cortisol (p = 0.004) were observed. Plasma aldosterone was 57% greater during exercise, while plasma cortisol did not change. The change in E and NE was greater at 0400 h, but this was due to the lower resting values of the catecholamines at 0400 h. These data indicate that time of day generally did not affect the hormonal or hemodynamic responses to exercise, with the exception that PRA was markedly higher during exercise at 1600 h compared to 0400 h.     

Effect of 17-alpha-hydroxyprogesteronecapronate on sodium excretion and the renin-angiotensin-aldosterone-system in humans]

In seven healthy male subjects, a natriuretic effect of 17 alpha-hydroxyprogesterone caproate (17 alpha-OHPC) was demonstrated. Three of these subjects were kept on an uncontrolled diet and were examined over a period of 12 days. To the remaining four subjects, a single dose of 250 mg 17 alpha-OHPC was given intramuscularly after four days of intake of a chemically defined diet (Vivasorb). In this second test procedure, blood samples were taken in the recumbent position every two hours throughout a period of 12 h after the injection. For two more days and during the days before the administration of 17 alpha-OHPC, blood was taken at 8 a.m. before getting up from bed in same intervals, urine was collected for analysis of sodium and potassium excretion. During the first 12 h after the injection of 17 alpha-OHPC, the urinary sodium/potassium ratio significantly increased in all subjects. Plasma renin activity showed no characteristic changes at this time, whereas the plasma concentrations of aldosterone and cortisol decreased. The decrease of cortisol concentration started immediately after the injection and was more pronounced than that of plasma aldosterone. During the following 36 h, renin activity as well as aldosterone and cortisol concentrations in plasma showed an increase; in contrast, the sodium/potassium ratio decreased. On the basis of these results, the following effects of 17 alpha-OHPC are discussed: (1) an acute natriuresis which may be due to a competitive inhibition of aldosterone at the renal tubules, and (2) an inhibition of pituitary ACTH secretion or of adrenal steroid biosynthesis.     

Plasma renin system during exercise in normal men

The exercise-related increase in plasma renin activity (PRA) and in the plasma concentration of angiotensin II (ANG II) and aldosterone (Aldo) was studied in 43 healthy volunteers whose 24-h urinary sodium excretion (UVNa) ranged from 10 to 250 mmol. Arterial blood samples were obtained at rest and during bicycle ergometry. Compared with rest, PRA, ANG II, and Aldo rose to a similar extent during light and moderate exercise. However, at peak exercise ANG II increased significantly more (P less than 0.001) than PRA and Aldo. Thus, with increasing intensity of exercise, the slope of the linear regression of ANG II on PRA became significantly (P less than 0.001) steeper, whereas at maximal exercise the Aldo response did not follow the acute rise in ANG II. At rest as well as during exercise, Aldo rose with increasing ANG II, but the stimulatory effect of ANG II on Aldo was attenuated with higher sodium intake, as estimated from UVNa. Finally, independent of the level of physical activity, UVNa was negatively correlated with PRA, ANG II, and Aldo.     

Magnesium homeostasis during high-intensity anaerobic exercise in men

This study was conducted to determine whether short-term, high-intensity anaerobic exercise alters Mg homeostasis. Thirteen men performed intermittent bouts of treadmill running at 90% of their predetermined maximum O2 uptake until exhaustion on one occasion during a week in which all men were consuming a standard diet (115 mg Mg/1,000 kcal). Plasma and erythrocyte Mg concentrations and peripheral blood mononuclear cell Mg content were measured before and after the exercise. Complete 24-h urine collections were obtained on control days, on the day of exercise, and on the day after exercise. Exercise induced a transient but significant decrease in plasma Mg content (-6.8%; P less than 0.01); over 85% of the loss could be accounted for by a shift to the erythrocytes. Significant increases in urinary excretion of Mg were observed on the day of exercise (131.5 +/- 6.8 mg/day) compared with control days (108 +/- 6.6 mg/day), with the percent increase correlating with postexercise blood lactate concentration (r = 0.68; P less than 0.01) and oxygen consumption during recovery (r = 0.84; P less than 0.001). The data indicate that high-intensity anaerobic exercise induces intercompartmental Mg shifts in blood that return to preexercise values within 2 h and urinary losses on the day of exercise that return to base line the day after exercise. It is postulated that the exercise-induced increase in Mg excretion may depend on the intensity of the exercise, and the relative contribution of anaerobic metabolism to the total energy expended during exercise.     

Effects of profuse sweating induced by exercise on urinary uric acid excretion in a hot environment

In order to determine whether exercise-induced profuse sweating could reduce urinary uric acid excretion, we simulated badminton players training and measured their uric acid in urine, sweat and blood during the training period. Thirteen male volunteers who were well-trained badminton players were recruited in this study. On the first 2 days and the last 2 days of the study period none of the subjects engaged in any intense exercise- or activity-inducing profuse sweat, but they accepted routine training 2 h per day during the middle 3 days. The results show that mean serum urate levels of thirteen volunteers rose significantly on day 4, when the concentrations increased by 18.2% over day 2 (P < 0.05). The mean ten-hour urinary uric acid excretion of seven volunteers on the 3 training days was significantly less at 178.5 micromol/day and 118.3 micromol/day than those on the preceding and subsequent days of the training days, respectively (P < 0.05). Furthermore, for six volunteers, the mean ratio of clearance of uric acid to creatinine was 6.6% on day 2, which significantly decreased to 5.4% on day 4 (P < 0.05). It is concluded profuse sweating exercise results in a decrease of urinary uric acid excretion amounts and leads to increased serum uric acid after the exercise. We suggest that persons who take vigorous exercise or are exposed to hot environments need drinking enough fluids to prevent dehydration and maintain adequate urinary output. People with profuse sweat after rigorous exercise are recommended taking sports drinks containing abundant sodium in order to decrease serum uric acid.     

Exercise effects on chromium excretion of trained and untrained men consuming a constant diet

Chromium excretion of eight trained and five sedentary men was determined on rest days and after exercise to exhaustion at 90% of maximum O2 consumption (VO2max) to determine if degree of physical fitness affects urinary Cr losses. Subjects were fed a constant daily diet containing approximately 9 micrograms Cr/1,000 kcal. VO2max of the trained runners was in the good or above range based on their age and that of the sedentary subjects was average or below. While consuming the control diet, basal urinary Cr excretion of subjects who exercise regularly was significantly lower than that of the sedentary control subjects, 0.09 +/- 0.01 and 0.21 +/- 0.03 microgram/day (mean +/- SE), respectively. When subjects consumed self-chosen diets, basal urinary Cr excretion of the trained subjects was also significantly lower than that of the untrained subjects. Daily urinary Cr excretion of trained subjects was significantly higher on the day of a single exercise bout at 90% VO2max compared with nonexercise days, 0.12 +/- 0.02 and 0.09 +/- 0.01 microgram/day, respectively. Urinary Cr excretion of sedentary subjects was not altered after controlled exercise. These data demonstrate that basal urinary Cr excretion and excretion in response to exercise are related to VO2max and therefore degree of physical fitness.     

Effect of a Single Bout of Exercise and β-Carotene Supplementation on the Urinary Excretion of 8-Hydroxy-deoxyguanosine in Humans

We investigated the effects of acute exhaustive exercise and β-carotene supplementation on urinary 8-hydroxy-deoxyguanosine (8-OHdG) excretion in healthy nonsmoking men. Fourteen untrained male (19-22 years old) volunteers participated in a double blind design. The subjects were randomly assigned to either the β-carotene or placebo supplement group. Eight subjects were given 30 mg of β-carotene per day for 1 month, while six subjects were given a placebo for the same period. All subjects performed incremental exercise to exhaustion on a bicycle ergometer both before and after the 1-month β-carotene supplementation period. The blood lactate and pyruvate concentrations significantly increased immediately after exercise in both groups. The baseline plasma p-carotene concentration was significantly 17-fold higher after β-carotene supplementation. The plasma β-carotene decreased immediately after both trials of exercise, suggesting that β-carotene may contribute to the protection of the increasing oxidative stress during exercise. Both plasma hypoxanthine and xanthine increased immediately after exercise before and after supplementation. This thus suggests that both trials of exercise might enhance the oxidative stress. The 24-h urinary excretion of 8-OHdG was unchanged for 3 days after exercise before and after supplementation in both groups. However, the baseline urinary excretion of 8-OHdG before exercise tended to be lower after β-carotene supplementation. These results thus suggest that a single bout of incremental exercise does not induce the oxidative DNA damage, while β-carotene supplementation may attenuate it.     

Influence of exposure to moderate altitude on the plasma concentraton of cortisol, aldosterone, renin, testosterone, and gonadotropins

The influence of 11 days at moderate altitude (2,000 m) combined with exercise on plasma concentration of testosterone, FSH (follicle-stimulating hormone), LH (luteinizing hormone), cortisol, aldosterone, and renin activity was studied in ten healthy subjects. Within 48 h of arrival at moderate altitude a significant increase in testosterone was found whereas FSH had decreased significantly and LH showed a tendency to decrease. Cortisol increased significantly at the beginning and reached a maximum at the end of altitude exposure. The plasma aldosterone level rose continuously and on the last day of altitude was significantly elevated. Plasma renin activity showed a tendency to decrease. On return to low land all measured parameters returned to base line values within 2 days. The findings of increases in plasma levels of aldosterone and testosterone (and serum T3 and T4, as reported by others) are in contrast to the previously found decrease of urinary excretion of all these hormones. This appears to be a distinct dissociation of serum levels of adrenal (and thyroid) hormones from their urinary excretion. The observed increase in plasma aldosterone is probably mediated through ACTH and the rise in plasma potassium, since plasma renin activity showed an opposite trend. The rise in plasma testosterone is probably of adrenal origin since plasma gonadotropins declined simultaneously. The increase of plasma levels of glucocorticoids, mineralocorticoids, and androgens after an ascent from 600 m to 2,000 m above sea level is compatible with an ACTH-mediated stimulation of the entire adrenal cortex and/or a diminished elimination of adrenal steroids: The concomitant fall of FSH, LH, and plasma renin would then be a consequence of a direct negative feedback inhibition of these hormones.     

Renal protein excretion after exercise in man

Thirteen men were submitted to graded exhaustive cycle exercise to determine the kinetics of proteinuria in the recovery period. Venous blood samples were analysed for haematocrit, lactate, creatinine, total protein and albumin for 1 h following exercise. Urine samples were collected during a 3-h recovery period. Total protein, albumin, and creatinine levels were determined for these samples. Total protein and albumin urinary excretion increased to 581 and 315 micrograms min-1, respectively, at the end of the 1st h of recovery as compared to 42 and 15 micrograms.min-1 for resting values. Plasma volume returned to pre-exercise levels between 30 and 60 min after cessation of exercise, while urinary total protein and albumin content still remained above the resting values for the following 2 h. Both post-exercise urinary total protein and albumin excretion followed a logarithmic decline with the same half-life of 54 min, thus requiring about 4 h to regain resting values. The reduction of plasma volume and the degree of dehydration do not seem to be involved in the process. The present study indicates the delayed recovery of protein handling by the kidney, as compared with other biochemical parameters, and provides accurate information on the kinetics of post-exercise proteinuria.     

Renal responsiveness to aldosterone during exposure to simulated microgravity.

We measured renal functions and hormones associated with fluid regulation after a bolus injection of aldosterone (Ald) during head-down tilt (HDT) bed rest to test the hypothesis that exposure to simulated microgravity altered renal responsiveness to Ald. Six male rhesus monkeys underwent two experimental conditions (HDT and control, 72 h each) with each condition separated by 9 days of ambulatory activities to produce a crossover counterbalance design. One test condition was continuous exposure to 10 degrees HDT; the second was a control, defined as 16 h per day of 80 degrees head-up tilt and 8 h prone. After 72 h of exposure to either test condition, monkeys were moved to the prone position, and we measured the following parameters for 4 h after injection of 1-mg dose of Ald: urine volume rate (UVR); renal Na(+)/K(+) excretion ratio; renal clearances of creatinine, Na(+), osmolality, and free water; and circulating hormones [Ald, renin activity (PRA), vasopressin (AVP), and atrial natriuretic peptide (ANP)]. HDT increased Na(+) clearance, total renal Na(+) excretion, urine Na(+) concentration, and fractional Na(+) excretion, compared with the control condition, but did not alter plasma concentrations of Ald, PRA, and AVP. Administration of Ald did not alter UVR, creatinine clearance, Ald, PRA, AVP, or ANP but reduced Na(+) clearance, total renal Na(+) excretion, urinary Na(+)/K(+) ratio, and osmotic clearance. Although reductions in Na(+) clearance and excretion due to Ald were greater during HDT than during control, the differential (i.e., interaction) effect was minimal between experimental conditions. Our data suggest that exposure to microgravity increases renal excretion of Na(+) by a natriuretic mechanism other than a change in renal responsiveness to Ald.     

Effects of acute intravenous aldosterone administration on Na(+), K(+), and water excretion in the horse.

The effect of a temporary increase in plasma aldosterone concentration on Na(+), K(+), and water balance was investigated in four horses. Aldosterone was injected intravenously for 6 h at 20-min intervals (total 5.4 microg/kg body wt). Samples were taken for 24 h before, during, and for 48 h after the treatment. Aldosterone treatment reduced the Na(+) loss via urine and feces by 99 and 72%, respectively, later followed by a marked increase in Na(+) excretion by both pathways. During the first 6 h after the treatment, fecal K(+) excretion was elevated, and the plasma K(+) concentration was lowered. Fluid was retained throughout the treatment period and for 12-15 h thereafter. In a second experiment, exercise was performed once after aldosterone treatment and once without prior treatment. Sweat samples were collected, and the composition was not altered after treatment. It was concluded that acute aldosterone injections reduce Na(+) losses in both feces and urine but not in sweat. In addition, the feces was shown to be the main excretion pathway of aldosterone.     

Plasma renin activity and serum aldosterone during prolonged physical strain. The significance of sleep and energy deprivation

Plasma renin activity (PRA), serum aldosterone and the serum and urinary levels of sodium and potassium have been investigated in 24 young men participating in a 5-day military training course with heavy continuous physical exercise, energy and sleep deprivation. The subjects were divided into three groups. Group 1 did not get any extra sleep or food, group 2 were compensated for the energy deficiency, and group 3 slept 3 h each night. The basic diet given to all the subjects was about 5,000 kJ and 2 g NaCl X 24 h-1 X cadet-1. The high calorie diet contained approximately 25,000-35,000 kJ and 20 g of NaCl X 24 h-1 X cadet-1. The study showed that serum aldosterone and PRA were extremely activated during such prolonged physical strain combined with lack of food and salt, whereas sleep deprivation did not seem to have any large influence. Only small variations were found in the serum levels of sodium and potassium and the urinary level of potassium during the course, whereas a decrease was seen in urinary sodium concentration. The fairly good correlations between the decrease in urinary sodium levels and the increase in PRA (r = 0.7) and further between PRA and serum aldosterone (r = 0.8) during the course indicate that there is a causal connection between the decrease in urinary sodium excretion and the increase in PRA and serum aldosterone.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of training on sweating responses during submaximal exercise in horses.

Sweating responses were examined in five horses during a standardized exercise test (SET) in hot conditions (32-34 degrees C, 45-55% relative humidity) during 8 wk of exercise training (5 days/wk) in moderate conditions (19-21 degrees C, 45-55% relative humidity). SETs consisting of 7 km at 50% maximal O(2) consumption, determined 1 wk before training day (TD) 0, were completed on a treadmill set at a 6 degrees incline on TD0, 14, 28, 42, and 56. Mean maximal O(2) consumption, measured 2 days before each SET, increased 19% [TD0 to 42: 135 +/- 5 (SE) to 161 +/- 4 ml. kg(-1). min(-1)]. Peak sweating rate (SR) during exercise increased on TD14, 28, 42, and 56 compared with TD0, whereas SRs and sweat losses in recovery decreased by TD28. By TD56, end-exercise rectal and pulmonary artery temperature decreased by 0.9 +/- 0.1 and 1.2 +/- 0.1 degrees C, respectively, and mean change in body mass during the SET decreased by 23% (TD0: 10.1 +/- 0.9; TD56: 7.7 +/- 0.3 kg). Sweat Na(+) concentration during exercise decreased, whereas sweat K(+) concentration increased, and values for Cl(-) concentration in sweat were unchanged. Moderate-intensity training in cool conditions resulted in a 1.6-fold increase in sweating sensitivity evident by 4 wk and a 0.7 +/- 0.1 degrees C decrease in sweating threshold after 8 wk during exercise in hot, dry conditions. Altered sweating responses contributed to improved heat dissipation during exercise and a lower end-exercise core temperature. Despite higher SRs for a given core temperature during exercise, decreases in recovery SRs result in an overall reduction in sweat fluid losses but no change in total sweat ion losses after training.     

Urine dopamine in starving obese subjects

In seven obese female subjects undergoing a period of therapeutic starvation, the excretion of sodium, potassium and dopamine and plasma levels of renin and aldosterone were measured. Sodium excretion increased during starvation and was maximal on the 2nd day. The urinary excretion of dopamine was significantly higher on day 4 and it remained elevated till the end of the study. Plasma renin activity and plasma aldosterone levels were also higher on the 4th-6th days of starvation. These findings suggest that dopamine may not play a significant role in the natriuresis of starvation.