Renal blood volume regulation in trained and untrained subjects during immersion

To study the cause of the increased blood volume of endurance-trained athletes we assessed the renal blood volume regulating mechanisms in eight untrained (UT) and eight endurance-trained (TR) male subjects during a 4 h head-out immersion. In TR plasma volume remained constant whereas it decreased in UT by 2.4 ml/kg (p less than 0.025). Immersion diuresis of TR was only half as high as in UT (peak values: 3.22 ml/min in UT, 1.60 ml/min in TR). Free water clearance remained approximately constant in UT but temporarily decreased in TR (p less than 0.001). This points to poor or even absent inhibition of antidiuretic hormone secretion in the latter group. Osmolar clearance increased less in TR than in UT (p less than 0.02) which was partly due to a delayed increase of glomerular filtration rate. Plasma osmolality, creatinine, and protein concentrations as well as hematocrit values were reduced during immersion to a similar extent in both groups. The results indicate a reduced renal response of endurance-trained subjects to congestion of the low-pressure system resulting in an increase in blood volume.     

Direct measurement of immunoreactive renin during changes of posture in man.

For several years, it has been possible to determine renin by a direct RIA. In the present study, plasma active renin concentration (PRC) was related to plasma renin activity (PRA) and aldosterone as a function of a standardized posture test. Using PRC, our target was to define the shortest necessary test duration. The three parameters were examined in 10 healthy male subjects (22-34 years old). Salt balance was determined in 24-hour urine, and plasma potassium and sodium were measured. Volunteers were hospitalized for 1 night, and at 8 a.m. the next morning they were subjected to the following postural changes: 3 h active orthostasis and 3 h recumbency. Frequent blood samples were taken. Orthostasis induced a significant rise in PRC, PRA and aldosterone already after 15 min. PRC and PRA reached a maximum level after 90 min of orthostasis and remained relatively stable, while aldosterone reached its highest level already after 30 min and then gradually decreased. Significant correlations were found between PRA and PRC (p < 0.001), between PRC and aldosterone (p < 0.001), and between PRA and aldosterone (p < 0.001). The PRC/PRA ratio changed during the course of the test, especially in supine subjects. When subjects returned to the supine position, all the parameters measured began a continual decrease. There were no significant changes in serum potassium and sodium levels throughout the duration of the test.(ABSTRACT TRUNCATED AT 250 WORDS)     

Renal responsiveness to aldosterone during exposure to head-down tilt bedrest

The kidneys represent a fundamental organ system responsible in part for the control of vascular volume. A 10% to 20% reduction in plasma volume is one of the fundamental adaptations during exposure to low gravity environments such as bedrest and space flight. Bedrest-induced hypovolemia has been associated with acute diuresis and natriuresis. Elevated baseline plasma renin activity and aldosterone levels have been observed in human subjects following exposure to head-down tilt and spaceflight without alterations in renal sodium excretion. Further, attempts to restore plasma volume with isotonic fluid drinking or infusion in human subjects exposed to head-down bedrest have failed. One explanation for these observations is that renal distal tubular cells may become less sensitive to aldosterone following exposure to head-down tilt, with a subsequent reduction in renal capacity for sodium retention. We hypothesized that elevated sodium and water excretion observed during prolonged exposure to bedrest and the subsequent inability to restore body fluids by drinking might be reflected, at least in part, by reduced renal tubular responsiveness to aldosterone. If renal tubular responsiveness to aldosterone were reduced with confinement to bedrest, then we would expect measures of renal sodium retention to be reduced when a bolus of aldosterone was administered in head-down tilt (HDT) bedrest compared to a control experimental condition. In order to test this hypothesis, we conducted an investigation in which we administered an acute bolus of aldosterone (stimulus) and measured responses in renal functions that included renal clearances of sodium and free water, sodium/potassium ratio in urine, urine sodium concentration, and total and fractional renal sodium excretion.     

Potassium loading effect on potassium balance in athletes during prolonged restriction of muscular activity

Negative potassium balance during hypokinesia (decreased number of kilometers taken/day) is not based on the potassium shortage in the diet, but on the impossibility of the body to retain potassium. To assess this hypothesis, we study the effect of potassium loading on athletes during prolonged hypokinesia (HK). Studies were done during 30 d of a pre-HK period and during 364 d of an HK period. Forty male athletes aged 23–26 yr were chosen as subjects. They were divided equally into four groups: unloaded ambulatory control subjects (UACS), unloaded hypokinetic subjects (UHKS), loaded hypokinetic subjects (LHKS), and loaded ambulatory control subjects (LACS). For the simulation of the hypokinetic effect, the LHKS and UHKS groups were kept under an average running distance of 1.7 km/d. In the LACS and LHKS groups, potassium loading tests were done by administering 95.35 mg KC1 per kg body weight. During the pre-HK and HK periods and after KC1 loading tests, fecal and urinary potassium excretion, sodium and chloride excretion, plasma potassium, sodium and chloride concentration, and potassium balance were measured. Plasma renin activity (PRA) and plasma aldosterone concentration was also measured. Negative potassium balance increased significantly (p < -0.01) in the UHKS and LHKS groups when compared with the UACS and LACS groups. Plasma electrolyte concentration, urinary electrolyte excretion, fecal potassium excretion, PRA, and PA concentration increased significantly (p ≤ 0.01) in the LHKS and UHKS groups when compared with LACS and UACS groups. Urinary and fecal potassium excretion increased much more and much faster in the LHKS group than in the UHKS group. By contrast, the corresponding parameters change insignificantly in the UACS and LACS groups when compared with the base line control values. It was concluded that urinary and fecal potassium excretion increased significantly despite the presence of negative potassium balance; thus, negative potassium balance may not be based on potassium shortage in the diet because of the impossibility of the body to retain potassium during HK.     

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)     

Renal effects of the acute inhibition of angiotensin-converting enzyme. I. 2) Studies during moderate potassium depletion]

We have investigated the relative roles of angiotensin II on the renal function and urinary excretion of some prostanoids in healthy women submitted to different conditions of potassium balance. To this aim we have evaluated the effects of an acute inhibition of angiotensin converting enzyme by enalapril (E). The renal function was explored by clearance (cl.) method during induced hypotonic polyuria (oral water load followed by 5% dextrose solution infusion). During 60 min cl. period the urinary PGE2, 6-keto-PGF1 alpha and TxB2 were determined by RIA method. Each subject received paired studies, in absence and presence of E (10 mg administered per os 1 hour before the water load). Basal values of plasma renin activity (PRA) and urinary aldosterone (excreted during the 24 hours before the water load) were also determined by RIA method. This study protocol was applied in normal potassium balance (n = 6) and induced moderate potassium depletion (n = 6). This paper concerns the group in potassium depletion in both absence (D4) and presence of E (D4.E). Potassium depletion was induced by adaptation to a normal sodium (150 mmol/d) and low potassium (< or = 10 mmol/d) dietary intake combined to natriuretic treatment. The water and NaCl net losses were restored by 0.9% NaCl solution infusion. The cumulative potassium deficit achieved at the end of the depletive treatment was 214 +/- 54 mmol. This treatment induced significant decrease in basal plasma potassium concentration and increase in PRA without affecting urinary aldosterone and plasma sodium concentration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of insulin on plasma concentration and renal excretion of sodium and potassium in normal, electrolytes depleted and aldosterone treated dogs

Effects of insulin on plasma concentration and renal excretion of sodium and potassium were compared in conscious dogs 1) maintained in water and electrolytes balance (Series 1, 10 dogs), 2) depleted of electrolytes by repeated i.v. loading with 20% mannitol (Series 2, 10 dogs), and 3) aldosterone treated (0.8 micrograms.kg-1.h-1 i.v., Series 3, 10 dogs). In each Series intravenous infusion of insulin at a rate of 0.05 U.kg-1.h-1 elicited transient increase in plasma sodium concentration and prolonged hypokalemia. Repeated loading with mannitol in Series 2 elicited significant elevation of plasma sodium, ADH and aldosterone concentrations, as well as decrease in extracellular fluid volume. Infusion of insulin in this Series elicited smaller decrease in plasma potassium concentration and longer lasting hypernatremia than in dogs in water-electrolytes balance. Aldosterone infusion in Series 3 did not change hypokalemic effect of insulin but attenuated hypernatremia. Infusion of insulin in Series 1 elicited increase of sodium excretion and decrease in potassium excretion. These effects were absent in Series 2 and 3. The results indicate that depletion of electrolytes and blood aldosterone elevation modify the effects of insulin on plasma concentration and renal excretion of sodium and potassium.     

Effect of hydration on plasma volume and endocrine responses to water immersion

To determine the effect of hydration on the early osmotic and intravascular volume and endocrine responses to water immersion the hematocrit, hemoglobin, plasma renin activity (PRA), and plasma electrolyte, aldosterone (PA), and vasopressin (PVP) concentrations were measured during immersion following 24-h dehydration; these were compared with corresponding values following rapid rehydration. Six men and one woman (age 23-46 yr) underwent 45 min of standing immersion to the neck preceded by 45-min standing without immersion, first dehydrated, and then 105 min later after rehydration with water. Immersion caused an isotonic expansion of the plasma volume (P less than 0.001), which occurred independently of hydration status. Suppression of PRA (P less than 0.001) and PA (P less than 0.001) during both immersions also occurred independently of hydration status. Suppression of plasma vasopressin was observed during dehydrated immersion (P less than 0.001) but not during rehydrated immersion. It is concluded that plasma tonicity is not a factor influencing PVP suppression during water immersion.     

Potassium supplements’ effect on potassium balance in athletes during prolonged hypokinetic and ambulatory conditions

Electrolyte supplements may be used to prevent changes in electrolyte balance during hypokinesia (diminished movement). The aim of this study was to measure the effect of potassium (K) supplements on K balance during prolonged hypokinesia (HK). Studies were done during 30 d of a pre-HK period and during 364 d of an HK period. Forty male athletes aged 25.1±4.4 yr were chosen as subjects. They were divided equally into four groups: unsupplemented ambulatory control subjects (UACS), unsupplemented hypokinetic subjects (UHKS), supplemented hypokinetic subjects (SHKS) and supplemented ambulatory control subjects (SACS). The SHKS and UHKS groups were kept under an average walking distance of 0.7 km/d. The SACS and SHKS groups were supplemented daily with 50.0 mg elemental potassium chloride (KCl) per kilogram body weight. The K balance, 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, anthropometric characteristics and peak oxygen uptake were measured. Negative K balance, fecal K excretion, urinary K, Na, and Cl excretion, plasma K, Na, and Cl concentration, and PRA and PA concentration increased significantly (p≤0.01), whereas body weight and peak oxygen uptake decreased significantly in the SHKS and UHKS groups when compared with SACS and UACS groups. However, the measured parameters changed much faster and much more in SHKS group than UHKS group. By contrast, K balance, fecal, urinary, and plasma K, plasma hormones, body weight, and peak oxygen uptake did not change significantly in the SACS and UACS groups when compared with the baseline control values. It was concluded that prolonged HK induces a significant negative K balance associated with increased plasma K concentration and urinary and fecal K excretion. However, negative K balance appeared much faster and was much greater in the SHKS group than UHKS group. Thus, K supplementation was not effective in preventing negative K balance during prolonged HK.     

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.     

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 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.     

Antigravity suit inflation: kidney function and cardiovascular and hormonal responses in men

To investigate the effects of lower body positive pressure (LBPP) on kidney function while controlling certain cardiovascular and endocrine responses, seven men [35 +/- 2 (SE) yr] underwent 30 min of sitting and then 4.5 h of 70 degrees head-up tilt. An antigravity suit was applied (60 Torr legs, 30 Torr abdomen) during the last 3 h of tilt. A similar noninflation experiment was conducted where the suited subjects were tilted for 3.5 h. To provide adequate urine flow, the subjects were hydrated during the course of both experiments. Immediately after inflation, mean arterial pressure increased by 8 +/- 3 Torr and pulse rate decreased by 16 +/- 3 beats/min. Plasma renin activity and aldosterone were maximally suppressed (P less than 0.05) after 2.5 h of inflation. Plasma vasopressin decreased by 40-50% (P less than 0.05) and plasma sodium and potassium remained unchanged during both experiments. Glomerular filtration rate was not increased significantly by inflation, whereas inflation induced marked increases (P less than 0.05) in effective renal plasma flow (ERPF), urine flow, osmolar and free water clearances, and total and fractional sodium excretion. No such changes occurred during control. Thus, LBPP induces 1) a significant increase in ERPF and 2) significant changes in kidney excretory patterns similar to those observed during water immersion or the early phase of bed rest, situations that also result in central vascular volume expansion.     

Fluid conservation in athletes: responses to water intake, supine posture, and immersion

The roles of antidiuretic hormone (ADH) and aldosterone in the elicited diuretic responses of trained and untrained men to seated, supine, and head-out water immersed conditions were studied. Volunteers were comprised of groups of six untrained individuals, six trained swimmers, and six trained runners. Each subject underwent three protocols, six hours in a seated position, supine position, or immersion (35 degrees C water). The last two protocols were preceded and followed by 1 h of seated position. After 10 h of fasting, 0.5% body wt of water was drunk. One hour later the trained groups had higher urine osmolalities (P less than 0.05) and urinary excretion rates of ADH (P less than 0.05) and lower urine flow rates (P less than 0.05) than untrained subjects. Throughout the sitting protocol, urinary ADH was also higher in both trained groups (P less than 0.05). Both supine posture and immersion resulted in significant decreases in urinary ADH in the untrained subjects (P less than 0.05) but no changes wer noted in swimmers and only during the second hour of immersion in the runners (P less than 0.05). The natriuresis and kaliuresis were greater during immersion than in the supine position but plasma renin activity, measured only in trained groups, and plasma aldosterone, measured in the untrained group, were decreased similarly with both protocols. The increases in urinary sodium excretion and urine flow rate were lower in trained than untrained subjects during the supine and immersion protocols (P less than 0.05). The data are compatible with an increased osmotic but decreased volume sensitivity of ADH control in trained men.     

Involvement of sodium retention hormones during rehydration in humans

We investigated the relation between involuntary dehydration and the mechanisms affecting Na+ retention in the body, focusing on the renin-angiotensin-aldosterone system. Six adult males were dehydrated to 2.3% of their body weight by an exercise-heat regimen, followed by rehydration (180 min) with tap water (H2O-R) or 0.45% NaCl solution (Na-R). We measured plasma renin activity (PRA) and aldosterone levels (PA) before dehydration (control), after dehydration, and at 60, 120, and 180 min of rehydration. During the 3-h rehydration period, subjects, restored 51% of the water lost during H2O-R and 71% during Na-R (P less than 0.05). Plasma volume was reduced by an average of 4.5% after dehydration. After 180 min of rehydration, plasma volume restoration during Na-R was to 174% of that lost, and during H2O-R it was to 78% of that lost. We found significant correlations between the change in plasma volume and PRA (r = -0.70, P less than 0.001) and between PRA and PA (r = 0.71, P less than 0.001). In both recovery conditions, PRA increased significantly after dehydration (P less than 0.05) and decreased almost to the control level by 180 min of rehydration, at which time the plasma volume deficit was restored. The change in PA paralleled that in PRA. The rate of sodium excretion was correlated with PA levels in both groups (r = -0.58, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Renal effects of the acute inhibition of angiotensin-converting enzyme. I. 1) Studies during normal sodium and potassium balance]

We have investigated the effective role of angiotensin II on the renal function and urinary excretion of some prostanoids in healthy women submitted to different conditions of potassium balance. To this aim we have evaluated the effects of an acute inhibition of angiotensin converting enzyme by enalapril (E). The renal function was explored by clearance (cl.) method during induced hypotonic polyuria (oral water load followed by 5% dextrose solution infusion). During 60 min cl. period the urinary PGE2, 6-keto-PGF1 alpha and TxB2 were determined by RIA method. Each subject received paired studies, in absence and presence of E (10 mg administered per os 1 hour before the water load). Basal values of plasma renin activity (PRA) and urinary aldosterone (excreted during the 24 hours before the water load) were also determined by RIA method. This study protocol was applied in normal potassium balance (n = 6) and induced moderate potassium depletion (n = 6). This paper concerns the group in normal potassium balance in both absence (N3) and presence of E (N3.E). All subjects were submitted to normal dietary intake of sodium (150 mmol/d) and potassium (50 mmol/d). The basal values of PRA, urinary aldosterone and plasma electrolytes were in the normal range. The only significant effect produced by E was a reduction in mean arterial pressure, without significant changes in creatinine cl., urinary hydro-electrolyte excretions as well as urinary excretions of prostanoids.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect on maternal and fetal renal function and plasma renin activity of a high salt intake by the ewe

The effect on renal function of replacing maternal drinking water with a solution containing 0.17 M NaCl was studied in 9 ewes and their chronically catheterised fetuses over a period of 9 days. Maternal sodium intake increased from control values of 2.19 +/- 0.09 mmol/h to 44.3 +/- 7.4 (P less than 0.001) and 46.3 +/- 6.5 mmol/h (P less than 0.001) on the 3rd and 6th days of salt ingestion. Maternal plasma sodium levels were not affected, but the urinary sodium/potassium ratio increased from 0.15 +/- 0.07 to 2.26 +/- 0.34 (P less than 0.001) after 6 days and plasma renin activity fell from 2.87 +/- 0.76 to 1.00 +/- 0.25 ng/ml per h (P less than 0.05). The changes in maternal sodium intake had no effect on fetal plasma sodium levels nor on fetal plasma renin activity. Sodium excretion and fetal urinary sodium/potassium ratio did not change. However, 3 days after the ewes returned to drinking water fetal plasma renin activity was significantly higher than it was prior to maternal ingestion of 0.17 M NaCl. Fetal plasma renin activity was inversely related to fetal plasma sodium levels (P less than 0.01). The results show that changes in maternal sodium intake had no long term effect on fetal plasma sodium levels nor on fetal renal sodium excretion. The fall in maternal plasma renin activity in the absence of any change in the fetal renin activity, indicates that the fetal renin angiotensin system is controlled by factors other than those influencing the maternal renin angiotensin system. Since fetal urinary sodium/potassium ratios remained unchanged it would suggest that fetal sodium excretion is not influenced by maternal levels of aldosterone.     

Influence of age on orthostatic changes in plasma renin activity and urinary catecholamines in man.

The authors studied plasma renin activity (PRA), urinary epinephrine, norepinephrine and dopamine excretion and their mutual relationships in 54 healthy subjects under basal (recumbent) conditions and age-related orthostatic changes in these parameters. The test subjects were divided into six 10-years groups, according to their year of birth (1901-1910 to 1951-1960). In the oldest groups (1901-1910 and 1911-1920), both basal PRA values and norephrine and epinephrine excretion and their postural increase were smaller than in younger subjects. Conversely, urinary dopamine excretion and the dopamine/norepinephrine and epinephrine ratio rose with advancing age. There were no significant differences between the plasma sodium and potassium concentrations in the various groups. Urinary aldosterone excretion was slightly higher in the oldest group than in the others, but was still within the control value limits. The intravenous administration of Inderal reduced both resting PRA values and the orthostatic increase in the youngest age groups, so that their PRA approached the values in older subjects. Higher norepinephrine and epinephrine excretion and the lower dopamine/norepinephrine and epinephrine in young subjects may play a role in their higher PRA, especially in the orthostatic reaction. Diminution of sympathetic activity, with lower norepinephrine and epinephrine excretion and relatively high dopamine excretion, may have a direct bearing on the lower PRA values in older subjects. The diminished capacity of older subjects for catecholamine mobilization and raised renin secretion during an orthostatis stress may be related to the higher incidence of orthostatic forms of hypotension in old age.     

Regulations of plasma aldosterone in young hyperkalemic patients with stable chronic renal failure.

In a group of four young patients with stable chronic renal failure and hyperkalemia sodium restriction induced a remarkable increase in plasma renin activity (PRA) and plasma aldosterone (PA), a decrease in the elevated serum potassium (SK) and a rise in potassium excretion. During high sodium intake the levels of PRA and PA were lower than those found in the healthy control group suggesting that enhanced suppressibility of the renin-angiotensin-aldosterone system (RAAS) was the main cause of hyperkalemia. During sodium restriction despite a marked increase in PRA and PA levels poor correlations were found between these variables indicating disorganisation within the RAAS and probably a diminished role for renin-angiotensin in the regulation of aldosterone production in three hyperkalemic patients with chronic glomerulonephritis. On the other hand, in the same patients significant correlations were found between fluctuations of SK and PA on constant normal and low sodium diets supporting the concept of an (at least) equal role of potassium and RAAS in the acute regulation of PA. A prominent role for SK was found in an unusual hyperkalemic patient with interstitial nephritis when PRA was suppressed and the elevated SK showed a definite postural rise inducing dramatic increases in PA in the upright posture. Reversion of the postural SK rise masked again the governing role of SK.     

Vasopressin inhibits diuresis induced by water immersion in humans.

We tested the hypothesis that 1-desamino-8-D-arginine vasopressin (DDAVP), a V2-receptor agonist, could inhibit the diuresis induced by water immersion in humans. Water and electrolyte excretion, plasma atrial natriuretic factor concentration, and plasma aldosterone concentration were measured initially and after 3 h of water immersion in 13 healthy sodium-replete men given either placebo or 20 micrograms of intranasal DDAVP. Guanosine 3',5'-cyclic monophosphate and urea excretion and urine osmolality were also determined. DDAVP inhibited the diuresis induced by water immersion in men: 758 +/- 168 (SE) ml/3 h in the placebo group vs. 159 +/- 28 ml/3 h in the DDAVP group (P less than 0.05). After 3 h of water immersion, plasma atrial natriuretic factor concentrations were increased from 11 +/- 2 to 20 +/- 4 pg/ml in the placebo group and from 14 +/- 2 to 33 +/- 4 pg/ml in the DDAVP group (P less than 0.05). Plasma aldosterone concentrations were decreased from 98 +/- 18 to 45 +/- 6 pg/ml in the placebo group (P less than 0.05) and from 54 +/- 17 to 25 +/- 5 pg/ml in the DDAVP group (P less than 0.05). Despite these changes in aldosterone and atrial natriuretic factor concentrations, which should increase sodium excretion, DDAVP decreased the natriuresis induced by water immersion in humans: 56 +/- 8 meq Na+/3 h in the placebo group vs. 36 +/- 6 meq Na+/3 h in the DDAVP group (P less than 0.05). DDAVP may be used to prevent the diuresis associated with central redistribution of blood volumes that occur during water immersion.(ABSTRACT TRUNCATED AT 250 WORDS)