Effect of water immersion on renin-aldosterone and renal sodium handling in normal man

Heat-induced hypervolemia: Does the mode of acclimation matter and what are the implications for performance at Tokyo 2020?

Tokyo 2020 will likely be the most heat stressful Olympics to date, so preparation to mitigate the effects of humid heat will be essential for performance in several of the 33 sports. One key consideration is heat acclimation (HA); the repeated exposure to heat to elicit physiological and psychophysical adaptations that improve tolerance and exercise performance in the heat. Heat can be imposed in various ways, including exercise in the heat, hot water immersion, or passive exposure to hot air (e.g., sauna). The physical requirements of each sport will determine the impact that the heat has on performance, and the adaptations required from HA to mitigate these effects. This review focuses on one key adaptation, plasma volume expansion (PVE), and how the mode of HA may affect the kinetics of adaptation. PVE constitutes a primary HA-mediated adaptation and contributes to functional adaptations (e.g., lower heart rate and increased heat loss capacity), which may be particularly important in athletes of "sub-elite" cardiorespiratory fitness (e.g., team sports), alongside athletes of prolonged endurance events. This review: i) highlights the ability of exercise in the heat, hot-water immersion, and passive hot air to expand PV, providing the first quantitative assessment of the efficacy of different heating modes; ii) discusses how this may apply to athletes at Tokyo 2020; and iii) provides recommendations regarding the protocol of HA and the prospect for achieving PVE (and the related outcomes).

Thiazolidinediones and the renal and hormonal response to water immersion-induced volume expansion in type 2 diabetes mellitus

Thiazolidinediones cause sodium retention and edema by a direct effect on the kidneys. The aim of this study was to use the technique of head-out water immersion to investigate the effects of rosiglitazone on sodium and volume homeostasis in subjects with type 2 diabetes mellitus. The volume expansion response to water immersion was compared with the response on a non-immersion control day in 12 nondiabetic male subjects and 8 diet-controlled male type 2 diabetic subjects with hourly blood and urine sampling over a 4-h period. This was repeated after both groups had taken 4 mg of rosiglitazone daily for 7 days. Immersion produced a natriuresis in both groups (P < 0.001). An impairment of this natriuresis was seen in the diabetic subjects (P = 0.006). However, when rosiglitazone was taken, there was no significant difference in immersion-induced natriuresis compared with nondiabetic controls (P = 0.2). There was an immersion-induced rise in atrial natriuretic peptide (ANP) and urinary cyclic guanosine monophosphate (cGMP), in the healthy subjects (ANP P = 0.001, cGMP P = 0.043), which was not seen in the diabetic subjects (ANP P = 0.51, cGMP P = 0.74). Rosiglitazone restored the immersion-induced increase in cGMP excretion and rise of ANP in the diabetic group (ANP P = 0.048, cGMP P = 0.009). This study confirms that type 2 diabetic subjects have an impaired natriuretic response to acute volume expansion, which appears to be enhanced rather than diminished by rosiglitazone. This may be related to its effects in increasing natriuretic peptides and restoring the impaired cGMP excretion to volume expansion.

Changes in the haemostatic system after thermoneutral and hyperthermic water immersion

Warm water bathing is a popular recreational activity and is frequently used in rehabilitation medicine. Although well tolerated in most cases, there are reports indicating an increased risk of thrombotic events after hot tub bathing. The effects of a 45 min thermoneutral bath followed by a 50 min bath with increasing water temperature (maximum 41 degrees C) until reaching a body core temperature of 39 degrees C on factors of blood coagulation and fibrinolysis were studied in eight healthy male volunteers. Blood was obtained after a 45-min resting period as control and after the thermoneutral and hyperthermic bath as well as after another 45 min recovery period at the end of the study. Hyperthermic immersion (HI) lead to a shortening of activated partial thromboplastin time (aPTT) (P < 0.05). Fibrinogen concentration decreased immediately after HI (P < 0.05) but increased during recovery (P < 0.05). Plasminogen activator inhibitor (PAI) activity decreased during HI (P < 0.05), D-dimer concentration was not found to change. Thrombocyte count increased (P < 0.05) during HI. The increases in tissue-type plasminogen activator concentration as well as leucocyte count during HI were due to haemoconcentration. Prothrombin time, PAI-activity and granulocyte count decreased during thermoneutral immersion (P < 0.05). Warm water bathing leads to haemoconcentration and minimal activation of coagulation. The PAI-1 activity is decreased. A marked risk for thrombotic or bleeding complications during warm water bathing in healthy males could not be ascertained.

Fluid volume compartments and biochemical measurements for disclosing fluid depletion during acute and rigorous bed rest in normal subjects

Rigorous bed rest (RBR) induces fluid depletion, however, little is known about the mechanisms of development of fluid depletion during acute bed rest (ABR). Measuring fluid retention and body hydration parameters, the aim of this study was to establish whether ABR than RBR could depress significantly more fluid retention contributing to greater fluid depletion development. Studies were conducted during pre bed rest (BR) period of three days and during seven days period of ABR and RBR. Thirty normal male individuals aged, 24.2 +/- 5.0 years chosen as subjects. They were divided into three groups: unrestricted ambulatory control subjects (UACS), acute bed rested subjects (ABRS) and rigorous bed rested subjects (RBRS). Acute bed rested subjects confined abruptly to RBR, while they did not have any prior knowledge of the exact date and time when they would be asked to stay in bed. Rigorous bed rested subjects submitted to RBR on a predetermined date and time known to them right from the start of the study. Unrestricted ambulatory control subjects were not confined to any type of bed rest. Fluid loss, urinary and plasma sodium (Na+) and potassium (K+), urinary osmolality and plasma osmolality, whole blood hematocrit (Hct), whole blood hemoglobin (Hb), and total plasma protein increased significantly (p < 0.05) with time, while fluid retention, extracellular volume (ECV), plasma volume (PV), red cell volume (RCV), blood volume (BV), interstitial volume (IV) and fluid intakes reduced significantly (p < 0.05) with time in ABRS and RBRS compared with their pre-BR values and the control values (UACS). However, the measured parameters changed significantly (p < 0.05) more with time in ABRS than RBRS. Fluid rention, fluid loss, fluid intake, urinary and plasma Na+ and K+, Hct, Hb, plasma protein, urinary and plasma osmolality, ECV, PV, RCV, BV and IV did not change in UACS compared with their pre-BR values. It was concluded that significant increase of urinary and plasma osmolality, whole blood Hct and Hb, total plasma protein, plasma Na+ and K+, and significant decrease of ECV, PV, RCV, BV, and IV may demonstrate fluid depleteion, while a higher increase of fluid loss in spite of fluid depletion may show decreased fluid retention. Dissociation between fluid losses and fluid depletion may suggest the presence of impair fluid retention as a mechanism of development of fluid depletion.

Angiotensin II attenuates the natriuresis of water immersion in humans

The hypothesis was tested that suppression of generation of ANG II is one of the mechanisms of the water immersion (WI)-induced natriuresis in humans. In one protocol, eight healthy young males were subjected to 3 h of 1) WI (WI + placebo), 2) WI combined with ANG II infusion of 0.5 ng. kg(-1). min(-1) (WI + ANG II-low), and 3) a seated time control (Con). In another almost identical protocol, 7-10 healthy young males were investigated to delineate the tubular site(s) of action of ANG II by the lithium clearance method (C(Li)) and were on an additional fourth study day subjected to infusion of ANG II at a rate of 1.5 ng. kg(-1). min(-1) (WI + ANG II-high). During WI + placebo, plasma concentration of ANG II decreased from 16 +/- 2 to 8 +/- 1 pg/ml (P < 0.05) and renal sodium excretion increased from 104 +/- 15 to 294 +/- 27 micromol/min (P < 0.05). During WI + ANG II-low, plasma ANG II was not suppressed by WI, and the natriuresis was blunted by 52 +/- 13% (P < 0.05). During WI + ANG II-low and WI + ANG II-high, an increase in C(Li) was prevented that was otherwise observed during WI, and fractional distal reabsorption of sodium was facilitated. In conclusion, maintaining plasma concentration of ANG II unchanged at the level of control attenuates the natriuresis of WI considerably in humans. Therefore, suppression of generation of ANG II is an important mechanism of the natriuresis of WI in humans. Furthermore, infusion of ANG II during WI prevents an otherwise induced increase in C(Li) and facilitates the fractional distal reabsorption of sodium, probably via an effect on aldosterone release.

Effects of aging on cardiovascular responses to gravity-related fluid shift in humans

BACKGROUND

Fluid shift induced by postural change causes autonomic neural responses of the cardiovascular system that buffer blood pressure fluctuation. The aim of the study was to clarify the effects of aging on cardiovascular autonomic functions in response to gravity-related fluid shift that unloads or loads the baroreceptors in human subjects.

METHODS

A chest electrocardiogram, blood pressure by Finapres, and stroke volume by impedance method were measured in healthy young men (23-31 years old) and healthy elderly men (74-80 years old) during supine rest, at 90 degrees head-up tilt and thermoneutral head-out water immersion. Spectral analysis was applied to the time series data of the R-R intervals (heart rate variability [HRV]) and systolic blood pressure (blood pressure variability [BPV]). The arterial baroreflex gain for heart rate was estimated using frequency transfer function analysis.

RESULTS

The young subjects had stable blood pressure, despite the larger amount of fluid shift induced by both tilt and immersion, and had marked changes in HRV and BPV. The elderly subjects failed to maintain stable blood pressure during these perturbations, despite less fluid shift and no significant changes in HRV and BPV. The arterial baroreflex gain for heart rate was not changed in the elderly subjects, whereas the gain decreased with upright in the young subjects and showed an increasing tendency during immersion compared with upright posture.

CONCLUSIONS

These findings suggest that the adaptivity of the autonomic nervous system to gravity-related fluid shift is reduced in elderly people, and this may cause blood pressure instability.

Cardiac Effects of Water Immersion in Healthy Volunteers

To evaluate cardiac chamber size and ejection fraction during head-out immersion of patients in the semisitting position in neutral temperature water bath, 12 volunteers were studied using transthoracic echocardiography (TTE). In this open, controlled, prospective clinical study, left ventricular end-systolic, end-diastolic volumes, and ejection fraction were measured in 12 adult awake healthy volunteers using TTE with the patient in a semisitting position pre-, during, and postimmersion in the Dornier extracorporeal shock wave lithotriptor water bath at 35 degrees C. Left ventricular end-diastolic volume significantly increased from an average of 96.0 +/- 10.8 to 130 +/- 19 cm(3), P < 0.0001 and left ventricular end-systolic volume increased from an average 38.9 +/- 6.9 to 45.2 +/- 8.0 cm(3), P < 0.01. Left ventricular ejection fraction increased significantly from control to water immersion from 0.59 +/- 0.1% to 0.65 +/- 0.1% (P < 0.001). The results of this study demonstrate that water immersion in normal healthy volunteers significantly increases both left ventricular diastolic and systolic volume, and that there is a significant increase in left ventricular ejection fraction after water immersion, (e.g., bathing, lithotripsy). While this increased cardiac filling is well-tolerated in most patients, it may not be well-tolerated in some patients who have limited cardiac reserve, including patients with heart failure.

Effect of physical exercise on renal response to head-out water immersion

Head-out water immersion (HOI) induces various renal functional changes, such as diuresis, natriuresis, and kaliuresis. The present study was undertaken 1) to characterize the renal response to HOI in Koreans who routinely ingest high salt diet and 2) to evaluate the impact of exercise on the renal response to HOI. Six healthy male subjects (average Na+ intake of 232 mEq.day-1) were immersed upto the neck in 34.5 degrees C water and rested in a seated position or exercised on a bicycle ergometer for 3 hours. In resting subjects, we observed a reversible increase in urine flow and a decrease in urine osmolality, with no changes in creatinine clearance. The peak urine flow observed during the second hour of immersion was 4-fold greater than the pre-immersion level. The excretion of total osmotic substances rose progressively during the 3-hour immersion, which was accompanied by a similar change in Na+ excretion. The K+ excretion was slightly elevated. The major component of the immersion diuresis was a water diuresis in the early phase and an osmotic diuresis in the late phase of immersion. In exercising subjects, the diuretic and natriuretic responses to HOI were attenuated and the kaliuretic response was potentiated. Blood hemoglobin concentration and plasma levels of renin, ADH, and aldosterone decreased during immersion-rest, but they remained unchanged or increased during immersion-exercise. These results suggest that 1) the cardiac mechanoreceptor-mediated renal responses to HOI are not changed by chronic high salt diet, and 2) excessive urinary sodium and water losses are prevented by exercise during immersion.

Renal sodium retention does not occur during the luteal phase of the menstrual cycle in normal women

OBJECTIVE

To determine whether weight gain due to renal sodium and water retention occurs in the luteal phase of the normal menstrual cycle.

DESIGN

Prospective observational study.

SETTING

Research laboratory installed with modified spa bath.

SUBJECTS

Ten normal healthy women.

INTERVENTION

Each subject underwent two experiments, one in each phase of the menstrual cycle, involving 3 h head-out water immersion and a pre- and post immersion control hour. 25 ml blood samples were obtained every hour before, during and after water immersion.

MAIN OUTCOME MEASURES

Renal and hormonal responses to water immersion during the luteal and proliferative phases of the cycle.

RESULTS

There was no change in weight, creatinine clearance, basal sodium excretion or plasma atrial natriuretic peptide between the two phases of the cycle. There was a significant rise in basal progesterone, plasma aldosterone and plasma renin activity in the luteal phase of the ovulatory cycles. Renal and hormonal responses to immersion including sodium and calcium excretion, elevation of atrial natriuretic peptide (ANP) and suppression of plasma aldosterone and plasma renin activity were identical in the two phases of the menstrual cycle.

CONCLUSION

We found no evidence to support the hypothesis that renal sodium and water retention occurs in the luteal phase of the normal menstrual cycle.

Atrial natriuretic peptide, renin and aldosterone in obstructive lung disease and heart failure

Elevations of atrial natriuretic peptide (ANP) in congestive heart failure (CHF) and chronic obstructive lung disease (COLD) are presumably due to atrial hypertension, while secondary hyperaldosteronism in these patients is thought to result from diminished renal perfusion. The responsiveness of the ANP and renin (PRA)-aldosterone (PA) systems to acute increases in right atrial pressure has not been studied in these patients, but in normals a reciprocal relationship between ANP with PRA and PA has been shown. The authors monitored venous pressure (VP, reflective of right atrial pressure), ANP, PRA and PA in 15 stable COLD patients, seven stable CHF patients and three normal controls at baseline and after elevation of VP by antishock trousers. Inflation of the trousers resulted in increased VP and ANP (p less than 0.05): control ANP, 84 +/- 17 to 108 +/- 23 pg/ml; COLD ANP, 176 +/- 5 to 200 +/- 7; and CHF ANP, 388 +/- 20 to 499 +/- 37. PRA and PA were not suppressed by increasing ANP levels and the delta ANP/delta VP ratio was similar among groups. No intergroup differences in resting PRA and PA were noted, but PRA was higher (p = 0.007) and PA tended to be higher (p = 0.08) in a sub-group of six edematous patients, as compared with non-edematous patients and controls. These findings: (1) confirm previously reported ANP differences between COLD and CHF; (2) indicate that the ANP system remains responsive to physiologic manipulations in COLD and CHF; and (3) demonstrate that ANP and the PRA-PA axis are not reciprocally related in either group.

Exercise versus immersion: antagonistic effects on water and electrolyte metabolism during swimming

Changes in blood composition, renal function, aldosterone and antidiuretic hormone (ADH) concentrations were investigated in 10 untrained male subjects when swimming (60 min at a heart rate of about 155 beats.min-1, water temperature 28 degrees C) and during the subsequent 3 h in a sitting position. Many specific effects of either exercise or immersion were abolished or attenuated; no significant changes in plasma aldosterone, [ADH], [K+], [Cl-], or of urinary volume, glomerular filtration rate, free water or osmolar clearance were observed. The urine was diluted resulting in lowered [Na+]. In blood some quantities which are only slightly influenced by immersion increased during swimming ([Na+], [Lac-], [H+], osmolality, [creatinine]). Exercise induced plasma volume loss, calculated from increasing [Hb], was small (110 ml), probably because interstitial fluid enters the vascular space during the initial phase of immersion. One might anticipate that the training effects on fluid and electrolyte metabolism and circulation are different when swimming and when performing endurance sports on land.

Head-down tilt as a physiological diuretic in normal controls and in patients with fluid-retaining states

The effect of the sitting, supine, supine with legs elevated 10 degrees, and 10 degrees head-down tilt postures on renal fluid and electrolyte handling was investigated in 14 patients with hypoalbuminaemic fluid-retaining states and in 14 normal individuals. Basal (sitting) urine volume, creatinine clearance, and urinary electrolyte levels were significantly lower in patients than in controls. In patients the values of these variables increased progressively from the sitting to the supine to the legs elevated to the head-down postures. The percentage rise was higher in patients than in controls, to the extent that, in the head-low position, only creatinine clearance values remained lower in patients than in controls. The head-down posture acts as a physiological diuretic, enhancing diuresis by improving renal function in normal individuals and in patients with ascites and oedema due to hypoalbuminaemia; it also corrects the abnormal fluid and sodium retention in these patients.

Effects of water immersion on renal function in the nephrotic syndrome

Nine adult patients with the nephrotic syndrome were studied during 4 hours of water immersion (WI) to the level of the neck in the seated position and under control conditions. During WI, sodium excretion (UNaV) rose from a mean prestudy level of 45.9 +/- 18.7 microEq/min to a mean peak level of 242.2 +/- 42.8 microEq/min during the 4th hour. During control studies, UNaV was unchanged. During WI, urine volume rose from 1.1 +/- 0.4 ml/min and reached a peak level of 7.5 +/- 0.8 ml/min during the 2nd hour. There were also marked increases in free water clearance and potassium excretion. Plasma renin activity fell from a prestudy level of 5.1 +/- 1.3 ng/ml/hr to a nadir of 1.9 +/- 0.4 ng/ml/hr during the 2nd hour of WI. Levels were unchanged during control studies. There was a considerable variation in the magnitude of the natriuretic effect of WI between the individual patients. Peak levels of UNaV varied from 55.3 to 488 microEq/min, and net negative sodium balance varied from 12.8 to 105 mEq. These variations were found to be directly related to the patient's estimated plasma volume, such that y = 19.2 chi - 211 (r = 0.84) represented the relationship between the plasma volume and the peak UNaV, and y = 1.9 chi - 41 (r = 0.81) represented the relationship between plasma volume and net negative sodium balance. These studies indicate that in patients with nephrotic syndrome, as in normal subjects, WI provides a potent natriuretic stimulus that results from expansion of the central blood volume. The magnitude of the natriuresis in nephrotic patients is related to their plasma volume, an observation that might help predict therapeutic benefit of the procedure in the individual patient.

Body fluid homeostasis in man. A contemporary overview

In the steady state, urinary excretion of sodium is closely matched to dietary salt intake. Given rigorous defense of extracellular fluid osmolality, it is the quantity of sodium in the extracellular fluid that determines the volume of this compartment. Changes in extracellular fluid volume are detected by volume sensors located in the intrathoracic vascular bed, kidney and other organs. These mechanoreceptors gauge the adequacy of intravascular volume, relative to capacitance, at various sites within the circulation. The perception of a change in the normal relationship between intravascular volume and circulatory capacity evokes a host of renal effector mechanisms that lead ultimately to physiologically appropriate changes in urinary sodium excretion. These effector mechanisms involve physical adjustments in the glomerular filtration rate, renal microvascular hemodynamics and peritubular capillary Starling forces, tubule fluid composition, flow rate and transtubular ion gradients. Neural and humoral pathways are also involved and, among the latter, angiotensin II, aldosterone, prostaglandins and kinins have been studied extensively. The continuous interaction between these sensor and effector mechanisms serves to ensure near-constancy of the extracellular fluid volume, a condition essential for optimal circulatory performance.

Early cardiovascular adaptation to zero gravity simulated by head-down tilt

The early cardiovascular adaptation to zero gravity, simulated by head-down tilt at 5 degrees, was studied in a series of 10 normal young men. The validity of the model was confirmed by comparing the results with data from Apollo and Skylab flights. Tilt produced a significant central fluid shift with a transient increase in central venous pressure, later followed by an increase in left ventricular size without changes in cardiac output, arterial pressure, or contractile state. The hemodynamic changes were transient with a nearly complete return to the control state within 6 hr. The adaptation included a diuresis and a decrease in blood volume, associated with ADH, renin and aldosterone inhibition.

Reduced aldosterone and sodium excretion in endurance-trained athletes before and during immersion

Aldosterone excretion (AE) and plasma renin activity (PRA) were measured in eight untrained (UT) and eight endurance-trained (TR) male subjects before and during 4 h head-out immersion to study the mechanism of reduced renal sodium excretion in athletes. AE was significantly lower before immersion, and decreased less during immersion, in TR than in UT. Fractional sodium excretion, too, was lower and increased less during immersion in TR than in UT. PRA decreased in the water bath in all subjects (p less than 0.001) with no significant difference between the groups. During immersion, plasma sodium concentration oscillated whereas potassium concentration showed a temporary rise in TR (p less than 0.001). The attenuated response of AE in TR may be due partly to this increase of plasma potassium concentration. The generally reduced aldosterone release in TR might be caused by a training induced adaptation of the adrenals to corticotropin. The lowered renal sodium excretion of TR in spite of the decreased AE suggests an intensified aldosterone effect in these subjects, diminishing the salt loss during exercise.

A review of the consequences of fluid and electrolyte shifts in weightlessness

This review describes the renal-endocrine mechanisms related to the early losses of fluid-electrolytes from the body during weightlessness as well as their contribution to longer term adaptation of fluid-electrolyte balance. The hypotheses presented were generated by a systematic analysis of body fluid and renal dynamics observed under conditions of actual and simulated spaceflight. These have increased our understanding of the effects of acute headward fluid shifts on renal excretion, the factors promoting excess sodium excretion and the regulation of extracellular fluid composition.

Modification of the normal postural changes in plasma renin activity by the application of positive pressure to the legs

In six normal male subjects plasma renin activity (PRA) rose progressively on standing over a 2 hour period. PRA fell to basal levels after a further 2 hours of recumbency. The rate of rise of PRA on standing was largely abolised following the application of an anti-gravity ('G') suit. Continuous monitoring of blood pressure (BP) heart rate (HR) and packed cell volume (PCV) suggest that it is the fall in effective blood volume which elicits the stimuli to renin release during changes in posture.

Total effective compliance, cardiac output and fluid volumes in essential hypertension

Total effective compliance, hemodynamic parameters, extracellular fluid volume, cardiopulmonary (CPBV) and total blood (TBV) volumes were determined in 32 men, including 14 normotensive controls and 18 sustained essential hypertensive patients. The effective compliance was calculated from the changes in central venous pressure recorded simultaneously with the changes in blood volume obtained after a rapid Dextran infusion. In normotensive controls, compliance was 2.08 +/- 0.09 ml/mm Hg/kg and was positively correlated with plasma (r = 0.79) and extracellular fluid (r = 0.84) volumes. In hypertensives, compliance was significantly reduced (1.49 +/- 0.06 ml/mm Hg/kg; P is less than 0.001) and was correlated negatively with the CPBV/TBV ratio (r = -0.75) and positively with the plasma volume/interstitial fluid volume ratio (r = 0.84). These results suggest that in normotensives, there is a regulatory mechanism between volume and compliance and that this contributes to maintaining filling pressure and cardiac output within normal ranges. In hypertensives, the reduced compliance could participate in the maintenance of normal values of cardiac output and extracellular fluid volume by influencing the partition of intravascular and extracellular fluid volumes.

Left atrial pressure and sodium balance in conscious dogs on a low sodium intake

10 conscious chronically prepared dogs were used. After recovery from thoracotomy (catheter into the left atrium, nylon purse string around the mitral annulus) they were kept chronically on a low sodium intake (less than 0.5 meq Na/kg bw daily). On 51 days left atrial pressure (LAP) was increased for 60 min about 10 cm H2O once daily by tightening the purse string (distension period: DP). During (DP) urine volume (V) increased about threefold, and sodium excretion (ENa) about sixfold. The amount of renal sodium loss on the days when LAP was increased exceeded the daily intake considerably. The application of DOCA (15 mg i.m.) did not diminish ENa during DP and 60 min therere increased by about 15 mm Hg. The data suggest that stimulation of intrathoracic receptors by a reversible mitral stenosis augments renal sodium excretion even in a state of a highly stimulated tubular sodium resorption.

Case reports and studies of paraneoplastic hypotension: abnormal low pressure baroreceptor responses

Intrathoracic stretch receptors regulate adjustments of the vasculature to gravitational changes and influence urinary water and solute excretion. Few reports of pathologic states involving interruption of these regulatory mechanisms have appeared. Two patients with orthostatic hypotenstion related to advanced intrathoracic carcinoma were studied, utilizing tilt-table examinations and immersion of the entire body in water to test the function of their intrathoracic baroreceptor reflex arcs. Both patients showed abnormalities of antidiuretic hormone level and sodium excretion as compared with normal controls. This suggests that total immersion is a safe and convenient test of the low-pressure baroreceptor system in patients with suspected dysfunction. Three patients are also reported whose charts were reviewed posthumously. Although they were not tested in the laboratory, their clinical data suggest that they too had been suffering from an interference with the transmission of impulses from the intrathoracic receptors.

Effect on plasma aldosterone, renin activity and cortisol of acute volume depletion induced by ethacrynic acid under constant infusion of angiotensin II and dexamethasone in man

The influence on plasma aldosterone of acute volume depletion induced by ethacrynic acid was studied in man. The experiments were performed during the morning in supine healthy males receiving a control infusion of 5% glucose or an infusion of angiotensin II (AII) to suppress endogenous renin production or an infusion of dexamethasone to suppress endogenous ACTH. Ethacrynic acid induced in all circumstances a similar diuresis and volume depletion. The rise of plasma renin activity (PRA) was effectively suppressed by AII and the rise of plasma cortisol by dexamethasone. Plasma aldosterone (PA) rose markedly even when the elevation of PRA or cortisol were suppressed. Yet when both endogenous renin and ACTH secretion were blocked, PA rose much less after ethacrynic acid. This residual increase could be attributed mainly to a decrease of the metabolic clearance rate (MCR) of aldosterone which had been measured before and after ethacrynic acid administration. The data presented indicate that multiple factors influencing PA after acute volume depletion could be dissected out and that renin, ACTH and a decrease of the MCR each contribute to the elevation of PA.

Recent advances in the physiology of whole body immersion

Recent investigations have furnished a complete analysis of the hemodynamic events accompanying whole-body immersion. About 700 ml of blood are translocated into the intrathoracic circulation, and heart volume increases by 180 +/- 62 ml. These changes are followed by an increase in stroke volume and cardiac output of over 30%. At the same time a reflex reduction of total peripheral resistance and venous tone occurs. Renin and aldosterone activity are reduced while the 17-hydroxycorticosteroid is not affected. Treatment of the subject with DOCA attenuates but does not extinguish the excess sodium excretion of immersion. This finding strengthens the arguments in favor of an unknown factor enhancing sodium excretion. Finally, the relative activation of the three factors that serve volume control, the excretory function of the kidney, capillary filtration pressure, and the thirst mechanism, is discussed.

The polyuria of paroxysmal atrial tachycardia

Two patients with paroxysmal atrial fibrillation and an associated polyuria were studied to delineate the mechanism of the increase in urine flow. A striking saluresis was noted in both patients. The increased sodium excretion was probably due to decreased sodium reabsorption, perhaps at proximal tubular nephron sites. This inhibition of sodium reabsorption could explain both the saluresis and some part or all of the polyuria. Re-evaluation of earlier case reports reveals patterns of concomitant salt and water excretion consistent with this mechanism. The saluresis cannot be explained by the previously favored hypothesis of antidiuretic hormone inhibition.

Impaired atrial receptor responses in dogs with heart failure due to tricuspid insufficiency and pulmonary artery stenosis

In a study of the effects of heart failure on the responses of cardiac receptors, ten dogs were subjected to tricuspid avulsion and pulmonary artery stenosis. One case of spontaneous heart failure was included in the series, and the electrical spike responses of atrial receptors to progressive changes in atrial stretch induced by infusion and hemorrhage were contrasted with those in normal control dogs. In the control dogs, the number of spikes per cycle increased very sharply with moderate, i.e., 5-10 cm H 2 O, venous pressure increments before reaching a maximum at 20 cm H 2 O. In the experimental dogs, the firing rate failed to increase to the same extent despite large increases in pressure. The resulting sets of curves exhibited a sharp dichotomy. This evidence for the impaired response of elements of the subendocardial receptor network is compatible with a decrease in the sensitivity of feedback mechanisms responsible for the regulation of sodium and water metabolism.

Role of mineralocorticoids in the natriuresis of water immersion in man

The role of aldosterone suppression in mediating the natriuresis of water immersion was assessed in six normal male subjects. All subjects were studied on four occasions while they were in balance on a diet containing 150 mEq of sodium and 100 mEq of potassium daily: during a control period, following deoxycorticosterone acetate (DOCA) treatment for 24 hours (Cont + DOCA), during water immersion to the neck (immersion), and during water immersion following DOCA treatment (Imm + DOCA). Immersion resulted in highly significant increases in the rates of sodium and potassium excretion compared with control beginning in the first hour. Although treatment with DOCA decreased the natriuresis of immersion ( P < 0.01), the rate of sodium excretion was still three- to fourfold greater during Imm + DOCA than it was during the comparable Cont + DOCA periods ( P < 0.01). Cessation of water immersion resulted in a marked decrease in urine flow and free water clearance occurring within the initial 30 minutes of recovery ( P < 0.005). Although the rate of sodium excretion also decreased following cessation of immersion, it continued to exceed both preimmersion values ( P < 0.01) and the comparable control values throughout the recovery hour ( P < 0.01). These observations suggest that the natriuresis of immersion cannot be completely accounted for by immersion-induced suppression of aldosterone. The continuing natriuresis occurring despite the progressive volume contraction induced by immersion suggests that the natriuretic stimulus is sufficiently potent to override the compensatory mechanisms which are known to participate in defense of volume homeostasis. Furthermore, the delay in the disappearance of the natriuresis suggests that a humoral factor rather than more rapidly acting hemodynamic and neural mechanisms may mediate the natriuresis.