Does gender influence human cardiovascular and renal responses to water immersion?

Cardiorespiratory Parameters Comparison Between Incremental Protocols Performed in Aquatic and Land Environments by Healthy Individuals: A Systematic Review and Meta-Analysis

BACKGROUND

Physical properties of water cause physiological changes in the immersed human body compared with the land environment. Understanding the magnitude of cardiorespiratory alterations might ensure adequate intensity control during aquatic exercise programs.

OBJECTIVE

We aimed to compare the oxygen uptake (VO₂), heart rate (HR), and rating of perceived exertion (RPE) parameters during aquatic and land incremental tests.

METHODS

Four databases (PubMed, LILACS, EMBASE, and SPORTDiscus) were searched in September 2020. Eligibility criteria included studies in a crossover design comparing aquatic and land incremental tests for healthy individuals with at least one of the following parameters: VO₂ (maximal, VO_2max; anaerobic threshold, VO_2AT), HR (HR_max; HR_AT), and RPE (RPE_max; RPE_AT). The random-effects meta-analysis included mean difference and 95% confidence interval for VO₂ and HR or standardized mean difference for RPE. The Joanna Briggs Institute Critical Appraisal tool was adapted to assess methodological quality.

RESULTS

Twenty-eight studies were eligible and included in the meta-analysis. Aquatic protocols showed lower values compared with land for VO_2max (- 7.07 mL.kg^-1.min^-1; - 8.43 to - 5.70; n = 502), VO_2AT (- 6.19 mL.kg^-1.min^-1; - 7.66 to - 4.73; n = 145), HR_max (- 11.71 bpm; - 13.84 to - 9.58; n = 503), and HR_AT (- 15.29 bpm; - 19.05 to - 11.53; n = 145). RPE_max (0.01; - 0.16 to 0.18; n = 299) and RPE_AT (- 0.67; - 1.35 to 0.02; n = 55) values were similar between aquatic and land protocols.

CONCLUSIONS

Our study reinforces the specificity of the environment during incremental tests for prescribing exercises based on physiological parameters as VO₂ and HR parameters presented lower values in aquatic protocols than land protocols. Conversely, RPE seems an interchangeable measure of exercise intensity, with similar values during the protocols in both environments. Substantial levels of heterogeneity were present for the VO_2max and HR_max meta-analyses, and as such, results should be interpreted with attention. PROTOCOL REGISTRATION: This study was registered in the International Prospective Register of Systematic Reviews (PROSPERO; CRD42020212508).

Application areas and effects of aquatic therapy WATSU - A survey among practitioners

INTRODUCTION

WATSU (WaterShiatsu) is a treatment administered in warm water. The present study investigated if and how frequently scientifically studied application areas and effects of WATSU occur in practice, whether similar effectiveness of WATSU is observed in trials and practice, and whether practitioners can contribute additional application areas and effects of WATSU.

METHODS

Application areas and effects of WATSU reported in a recent systematic review were extracted verbatim to be assessed in a worldwide multilingual cross section online survey, generating quantitative and qualitative data. A pre-test and retest were conducted to ensure quality and evaluate the questionnaire's psychometric properties.

RESULTS

Answers of 191 respondents were processed. All proposed 26 application areas and 20 effects were confirmed, each with relatively high ratings of observed effectiveness of WATSU. WATSU was frequently applied in healthy individuals (including during pregnancy), and individuals in various pain- (e.g., low back pain, neck pain, myofascial pain, fibromyalgia) and stress-related (e.g., stress, depression, sleep disorders, fatigue, anxiety disorders) conditions. Frequently confirmed effects were physical relaxation, relief of physical tension, pain relief, increased mobility and flexibility, improved quality of life, spiritual experiences, and increased psychological health. Respondents contributed 73 additional application areas and effects (both, mental and physical) of WATSU.

CONCLUSIONS

Application areas and effects of WATSU are consistently employed practically and scientifically. Respondents' ratings of effectiveness of WATSU match tentative research efforts. WATSU is cautiously recommended for the use in pain- and stress-related conditions. Short- and long-term effectiveness of WATSU need to be evaluated in high level intervention studies.

"The immediate effect of neutral spinal compress on heart rate variability in hypertensive individuals"

OBJECTIVES

Hypertension (HTN) is considered as chronic medical condition. Because of the increased complications associated with the conventional medicine, the effects of naturopathic modalities were emphasized to prevent and minimize those adverse effects. This study was done to assess the immediate effect of neutral spinal compress on heart rate variability and blood pressure and thereby to substantiate the clinical understanding of its effect in hypertensive individuals.

METHODS

Hundred hypertensive individuals were recruited for the study. Subjects were assessed for Blood Pressure (BP) and Heart Rate Variability (HRV) before and immediately after the intervention of 20 min.

RESULTS

Result shows significant reduction in mean Heart Rate (HR) (p<0.001), Low Frequency (LF) (p<0.001), Low Frequency/High Frequency (LF/HF) (p<0.001), Systolic blood pressure (SBP) (p<0.001) and Diastolic blood pressure (DBP) (p<0.001) and significant increase in mean R-R interval (Mean RR) (p<0.001) and High frequency (HF) (p<0.001) components of Heart Rate Variability after neutral spinal compress intervention.

CONCLUSIONS

The results of the study reported that full neutral spinal compress reduces the sympathetic tone and shifts the Sympatho-vagal balance in favor of parasympathetic dominance and hence it can be concluded that neutral spinal compress can be effectively used in the management of hypertension.

TRIAL REGISTRATION

Clinical Trial Registry- India (CTRI); CTRI Reg. No- CTRI/2020/01/022639.

The effect of water immersion and acute hypercapnia on ventilatory sensitivity and cerebrovascular reactivity

The partial pressure of end tidal carbon dioxide (PETCO2 ), ventilatory sensitivity to CO2 , and cerebral perfusion are augmented during thermoneutral head out water immersion (HOWI). We tested the hypotheses that HOWI and acute hypercapnia augments minute ventilation, ventilatory sensitivity to CO2 , cerebral perfusion, and cerebrovascular reactivity to CO2 . Twelve subjects (age: 24 ± 3 years, BMI: 25.3 ± 2.9 kg/m2 , 6 women) participated in two experimental visits: a HOWI visit (HOWI) and a matched hypercapnia visit (Dry + CO2 ). A rebreathing test was conducted at baseline, 10, 30, 60 min, and post HOWI and Dry + CO2 . PETCO2 , minute ventilation, expired gases, blood pressure, heart rate, and middle cerebral artery blood velocity were recorded continuously. PETCO2 increased throughout HOWI (baseline: 42 ± 2 mmHg; maximum at 10 min: 44 ± 2 mmHg, P ≤ 0.013) and Dry + CO2 (baseline: 42 ± 2 mmHg; maximum at 10 min: 44 ± 2 mmHg, P ≤ 0.013) and was matched between conditions (condition main effect: P = 0.494). Minute ventilation was lower during HOWI versus Dry + CO2 (maximum difference at 60 min: 13.2 ± 1.9 vs. 16.2 ± 2.7 L/min, P < 0.001). Ventilatory sensitivity to CO2 and middle cerebral artery blood velocity were greater during HOWI versus Dry + CO2 (maximum difference at 10 min: 2.60 ± 1.09 vs. 2.20 ± 1.05 L/min/mmHg, P < 0.001, and 63 ± 18 vs. 53 ± 14 cm/sec, P < 0.001 respectively). Cerebrovascular reactivity to CO2 decreased throughout HOWI and Dry + CO2 and was not different between conditions (condition main effect: P = 0.777). These data indicate that acute hypercapnia, matched to what occurs during HOWI, augments minute ventilation but not ventilatory sensitivity to CO2 or middle cerebral artery blood velocity despite an attenuated cerebrovascular reactivity to CO2 .

Peripheral chemosensitivity is not blunted during 2 h of thermoneutral head out water immersion in healthy men and women

Carbon dioxide (CO₂) retention occurs during water immersion, but it is not known if peripheral chemosensitivity is altered during water immersion, which could contribute to CO₂ retention. We tested the hypothesis that peripheral chemosensitivity to hypercapnia and hypoxia is blunted during 2 h of thermoneutral head out water immersion (HOWI) in healthy young adults. Peripheral chemosensitivity was assessed by the ventilatory, heart rate, and blood pressure responses to hypercapnia and hypoxia at baseline, 10, 60, 120 min, and post HOWI and a time‐control visit (control). Subjects inhaled 1 breath of 13% CO₂, 21% O₂, and 66% N₂ to test peripheral chemosensitivity to hypercapnia and 2–6 breaths of 100% N₂ to test peripheral chemosensitivity to hypoxia. Each gas was administered four separate times at each time point. Partial pressure of end‐tidal CO₂ (PETCO₂), arterial oxygen saturation (SpO₂), ventilation, heart rate, and blood pressure were recorded continuously. Ventilation was higher during HOWI versus control at post (P = 0.037). PETCO₂ was higher during HOWI versus control at 10 min (46 ± 2 vs. 44 ± 2 mmHg), 60 min (46 ± 2 vs. 44 ± 2 mmHg), and 120 min (46 ± 3 vs. 43 ± 3 mmHg) (all P < 0.001). Ventilatory (P = 0.898), heart rate (P = 0.760), and blood pressure (P = 0.092) responses to hypercapnia were not different during HOWI versus control at any time point. Ventilatory (P = 0.714), heart rate (P = 0.258), and blood pressure (P = 0.051) responses to hypoxia were not different during HOWI versus control at any time point. These data indicate that CO₂ retention occurs during thermoneutral HOWI despite no changes in peripheral chemosensitivity.

Post-exercise hypotension and heart rate variability response after water- and land-ergometry exercise in hypertensive patients

BACKGROUND

systemic arterial hypertension is the most prevalent cardiovascular disease; physical activity for hypertensive patients is related to several beneficial cardiovascular adaptations. This paper evaluated the effect of water- and land-ergometry exercise sessions on post-exercise hypotension (PEH) of healthy normotensive subjects versus treated or untreated hypertensive patients.

METHODS

Forty-five older women composed three experimental groups: normotensive (N, n = 10), treated hypertensive (TH, n = 15) and untreated hypertensive (UH, n = 20). The physical exercise acute session protocol was performed at 75% of maximum oxygen consumption (VO2max) for 45 minutes; systolic (SBP), diastolic (DBP) and mean (MBP) blood pressure were evaluated at rest, peak and at 15, 30, 45, 60, 75 and 90 minutes after exercise cessation. Additionally, the heart rate variability (HRV) was analyzed by R-R intervals in the frequency domain for the assessment of cardiac autonomic function.

RESULTS

In both exercise modalities, equivalent increases in SBP were observed from rest to peak exercise for all groups, and during recovery, significant PEH was noted. At 90 minutes after the exercise session, the prevalence of hypotension was significantly higher in water- than in the land-based protocol. Moreover, more pronounced reductions in SBP and DBP were observed in the UH patients compared to TH and N subjects. Finally, exercise in the water was more effective in restoring HRV during recovery, with greater effects in the untreated hypertensive group.

CONCLUSION

Our data demonstrated that water-ergometry exercise was able to induce expressive PEH and improve cardiac autonomic modulation in older normotensive, hypertensive treated or hypertensive untreated subjects when compared to conventional land-ergometry.

Human Physiology in an Aquatic Environment

Water covers over 70% of the earth, has varying depths and temperatures and contains much of the earth's resources. Head-out water immersion (HOWI) or submersion at various depths (diving) in water of thermoneutral (TN) temperature elicits profound cardiorespiratory, endocrine, and renal responses. The translocation of blood into the thorax and elevation of plasma volume by autotransfusion of fluid from cells to the vascular compartment lead to increased cardiac stroke volume and output and there is a hyperperfusion of some tissues. Pulmonary artery and capillary hydrostatic pressures increase causing a decline in vital capacity with the potential for pulmonary edema. Atrial stretch and increased arterial pressure cause reflex autonomic responses which result in endocrine changes that return plasma volume and arterial pressure to preimmersion levels. Plasma volume is regulated via a reflex diuresis and natriuresis. Hydrostatic pressure also leads to elastic loading of the chest, increasing work of breathing, energy cost, and thus blood flow to respiratory muscles. Decreases in water temperature in HOWI do not affect the cardiac output compared to TN; however, they influence heart rate and the distribution of muscle and fat blood flow. The reduced muscle blood flow results in a reduced maximal oxygen consumption. The properties of water determine the mechanical load and the physiological responses during exercise in water (e.g. swimming and water based activities). Increased hydrostatic pressure caused by submersion does not affect stroke volume; however, progressive bradycardia decreases cardiac output. During submersion, compressed gas must be breathed which introduces the potential for oxygen toxicity, narcosis due to nitrogen, and tissue and vascular gas bubbles during decompression and after may cause pain in joints and the nervous system.

Active Female Maximal and Anaerobic Threshold Cardiorespiratory Responses to Six Different Water Aerobics Exercises

PURPOSE

Maximal tests conducted on land are not suitable for the prescription of aquatic exercises, which makes it difficult to optimize the intensity of water aerobics classes. The aim of the present study was to evaluate the maximal and anaerobic threshold cardiorespiratory responses to 6 water aerobics exercises. Volunteers performed 3 of the exercises in the sagittal plane and 3 in the frontal plane.

METHOD

Twelve active female volunteers (aged 24 ± 2 years) performed 6 maximal progressive test sessions. Throughout the exercise tests, we measured heart rate (HR) and oxygen consumption (VO2). We randomized all sessions with a minimum interval of 48 hr between each session. For statistical analysis, we used repeated-measures 1-way analysis of variance.

RESULTS

Regarding the maximal responses, for the peak VO2, abductor hop and jumping jacks (JJ) showed significantly lower values than frontal kick and cross-country skiing (CCS; p < .001; partial η(2) = .509), while for the peak HR, JJ showed statistically significantly lower responses compared with stationary running and CCS (p < .001; partial η(2) = .401). At anaerobic threshold intensity expressed as the percentage of the maximum values, no statistically significant differences were found among exercises.

CONCLUSION

Cardiorespiratory responses are directly associated with the muscle mass involved in the exercise. Thus, it is worth emphasizing the importance of performing a maximal test that is specific to the analyzed exercise so the prescription of the intensity can be safer and valid.

Body height and blood pressure regulation in humans during anti-orthostatic tilting

The hypothesis was tested that the cardiovascular changes during an upper body anti-orthostatic maneuver in humans are more pronounced in tall than in short individuals, because of the larger intravascular hydrostatic pressure gradients. In 34 males and 41 females [20–30 yr, body height (BH) = 147–206 cm], inter-individual multiple linear regression analyses adjusted for gender and body weight were conducted between changes in cardiovascular variables versus BH during tilting of the upper body from vertical to horizontal while keeping the legs horizontal. In all the subjects, tilting induced increases in stroke volume and arterial pulse pressure and a decrease in heart rate, which each correlated significantly with BH. In males ( n = 51, BH = 163–206 cm), 24-h ambulatory mean arterial pressure increased significantly with BH ( P = 0.004, r = 0.40, α = 0.15 mmHg/cm) so that systolic/diastolic blood pressure increased by 2/2 mmHg per 15 cm increase in BH. There was no significant correlation between mean arterial pressure and BH in females ( n = 53, BH = 147–193 cm). In conclusion, a larger BH induces larger cardiovascular changes during anti-orthostatic tilting, and in males 24-h ambulatory mean arterial pressure increases with BH. The lack of a mean arterial pressure to BH correlation in females is probably because of their lower BH and greater variability in blood pressure.

Influência da imersão nas respostas cardiorrespiratórias em repouso

Diversos benefícios nos componentes da aptidão física podem ser adquiridos com a prática de exercícios aquáticos. Além disso, a água proporciona um ambiente para a prática de exercícios com reduzido impacto nos membros inferiores e maior ou menor sobrecarga cardiorrespiratória, de acordo com os movimentos realizados. Porém, tais exercícios podem produzir respostas fisiológicas diferentes daquelas ao ar livre, visto que ocorrem alterações fisiológicas importantes durante a imersão, sendo importante a compreensão das mesmas em repouso para melhor prescrição nesse meio. O presente estudo tem como objetivo revisar estudos sobre o comportamento da frequência cardíaca e do consumo de oxigênio durante a imersão em repouso e compreender os fatores que influenciam nesse comportamento. Várias pesquisas indicam que a frequência cardíaca de repouso é reduzida com a imersão em meio aquático, porém, é importante salientar que fatores tais como temperatura da água, posição corporal, profundidade de imersão e frequência cardíaca inicial podem minimizar ou maximizar tais respostas. Os estudos que abordaram as respostas de consumo de oxigênio não são conclusivos; entretanto, ao contrário da frequência cardíaca, os mesmos indicam semelhante ou maior resposta durante a imersão em repouso. Assim, pode-se concluir que, devido às alterações cardiorrespiratórias verificadas com a imersão em ambiente aquático, a prescrição de exercícios nesse meio deve ser diferenciada daquela para exercícios em ambiente terrestre.

The underwater environment: cardiopulmonary, thermal, and energetic demands

Water covers over 75% of the earth, has a wide variety of depths and temperatures, and holds a great deal of the earth's resources. The challenges of the underwater environment are underappreciated and more short term compared with those of space travel. Immersion in water alters the cardio-endocrine-renal axis as there is an immediate translocation of blood to the heart and a slower autotransfusion of fluid from the cells to the vascular compartment. Both of these changes result in an increase in stroke volume and cardiac output. The stretch of the atrium and transient increase in blood pressure cause both endocrine and autonomic changes, which in the short term return plasma volume to control levels and decrease total peripheral resistance and thus regulate blood pressure. The reduced sympathetic nerve activity has effects on arteriolar resistance, resulting in hyperperfusion of some tissues, which for specific tissues is time dependent. The increased central blood volume results in increased pulmonary artery pressure and a decline in vital capacity. The effect of increased hydrostatic pressure due to the depth of submersion does not affect stroke volume; however, a bradycardia results in decreased cardiac output, which is further reduced during breath holding. Hydrostatic compression, however, leads to elastic loading of the chest wall and negative pressure breathing. The depth-dependent increased work of breathing leads to augmented respiratory muscle blood flow. The blood flow is increased to all lung zones with some improvement in the ventilation-perfusion relationship. The cardiac-renal responses are time dependent; however, the increased stroke volume and cardiac output are, during head-out immersion, sustained for at least hours. Changes in water temperature do not affect resting cardiac output; however, maximal cardiac output is reduced, as is peripheral blood flow, which results in reduced maximal exercise performance. In the cold, maximal cardiac output is reduced and skin and muscle are vasoconstricted, resulting in a further reduction in exercise capacity.

Physiological response to water immersion: a method for sport recovery?

Recovery from exercise can be an important factor in performance during repeated bouts of exercise. In a tournament situation, where athletes may compete numerous times over a few days, enhancing recovery may provide a competitive advantage. One method that is gaining popularity as a means to enhance post-game or post-training recovery is immersion in water. Much of the literature on the ability of water immersion as a means to improve athletic recovery appears to be based on anecdotal information, with limited research on actual performance change. Water immersion may cause physiological changes within the body that could improve recovery from exercise. These physiological changes include intracellular-intravascular fluid shifts, reduction of muscle oedema and increased cardiac output (without increasing energy expenditure), which increases blood flow and possible nutrient and waste transportation through the body. Also, there may be a psychological benefit to athletes with a reduced cessation of fatigue during immersion. Water temperature alters the physiological response to immersion and cool to thermoneutral temperatures may provide the best range for recovery. Further performance-orientated research is required to determine whether water immersion is beneficial to athletes.

Degassed liquids to prevent/treat decompression sickness

Recompression and oxygen breathing constitute the primary treatments for decompression sickness (DCS). Increasing the volume of distribution of dissolved gas with high-volume liquid therapy represents an alternative strategy to prevent or treat DCS. Furthermore, degassing of ingested and infused liquids would increase their potential to keep supersaturated tissue gases in solution after decompression. We hypothesize that administration of degassed liquids will prevent or reverse mild-moderate DCS by increasing the volume of distribution of dissolved gas in DCS victims. Degassed perfluorocarbon ingestion offers particularly attractive potential: one liter theoretically dissolves approximately 300ml of N(2) in vivo at 1atm. One could speculate that degassed liquids may adequately treat mild DCS in lieu of recompression, particularly DCS expressed in 'fast compartment' (well-perfused) tissues. Furthermore, degassed liquid administration should prove to be even more effective adjunct therapy for severe DCS than present gas-saturated liquids.

Influence of sex on the relation between heart rate and aortic stiffness

BACKGROUND

Heart rate and aortic pulse wave velocity (PWV) are both cardiovascular risk factors. The aim of this study was to evaluate the influence of sex on the heart rate-PWV relationship in two populations of normotensive and hypertensive men and women.

PATIENTS AND METHODS

In a first study, steady-state data describing the heart rate-PWV relationship were determined in 558 normotensive men, 308 normotensive women, 323 hypertensive men and 93 hypertensive women. In a second study, the changes in blood pressure and PWV under atrial pacing at 60, 80 and 100 beats/min were investigated in 15 men and 15 women who were either normotensive or hypertensive.

RESULTS

In women in study 1, 26.8% of PWV variance in normotensive patients and 15.4% of PWV variance in hypertensive patients was explained by a multiple regression including only age and systolic blood pressure as covariates. In men in study 1, 27% of PWV variance in normotensive patients and 28.5% of PWV variance in hypertensive patients was explained by a multiple regression including age, systolic blood pressure, weight, and also heart rate, as covariates. In study 2, atrial pacing in the overall population tended to decrease mean blood pressure (P = 0.05) and increase pulse pressure (P = 0.003), with no substantial change in PWV. However, when heart rate increased, PWV tended to decrease in women and to increase in men (interaction: P = 0.07).CONCLUSION Accelerated heart rate influences PWV in both normotensive and hypertensive men and, through this mechanism, could influence cardiovascular risk. However, heart rate does not influence PWV in women.

Sex differences in osmotic regulation of AVP and renal sodium handling

To determine sex differences in osmoregulation of arginine vasopressin (AVP) and body water, we studied eight men (24 +/- 1 yr) and eight women (29 +/- 2 yr) during 3% NaCl infusion [hypertonic saline infusion (HSI); 120 min, 0.1 ml. kg body wt(-1). min(-1)]. Subjects then drank 15 ml/kg body wt over 30 min followed by 60 min of rest. Women were studied in the early follicular (F; 16.1 +/- 2.8 pg/ml plasma 17beta-estradiol and 0.6 +/- 0.1 ng/ml plasma progesterone) and midluteal (L; 80.6 +/- 11.4 pg/ml plasma 17beta-estradiol and 12.7 +/- 0.7 ng/ml plasma progesterone) menstrual phases. Basal plasma osmolality was higher in F (286 +/- 1 mosmol/kgH(2)O) and in men (289 +/- 1 mosmol/kgH(2)O) compared with L (280 +/- 1 mosmol/kgH(2)O, P < 0.05). Neither menstrual phase nor gender affected basal plasma AVP concentration (P([AVP]); 1.7 +/- 4, 1.9 +/- 0.4, and 2.2 +/- 0.5 pg/ml for F, L, and men, respectively). The plasma osmolality threshold for AVP release was lowest in L (x-intercept, 263 +/- 3 mosmol/kgH(2)O, P < 0.05) compared with F (273 +/- 2 mosmol/kgH(2)O) and men (270 +/- 4 mosmol/kgH(2)O) during HSI. Men had greater P([AVP])-plasma osmolality slopes (i.e., sensitivity) compared with F and L (slopes = 0.14 +/- 0.04, 0.09 +/- 0.01, and 0.24 +/- 0.07 for F, L, and men, respectively, P < 0.05). Despite similar Na+-regulating hormone responses, men excreted less Na+ during HSI (0.7 +/- 0.1, 0.7 +/- 0.1, and 0.5 +/- 0.1 meq/kg body wt for F, L, and men, respectively, P < 0.05). Furthermore, men had greater systolic blood pressure (119 +/- 5, 119 +/- 5, and 132 +/- 3 mmHg for F, L, and men, respectively, P < 0.05) than F and L. Our data indicate greater sensitivity in P([AVP]) response to changes in plasma osmolality as the primary difference between men and women during HSI. In men, this greater sensitivity was associated with an increase in systolic blood pressure and pulse pressure during HSI, most likely due to a shift in the pressure-natriuresis curve.

Fluid volume and osmoregulation in humans after a week of head-down bed rest

Body fluid homeostasis was investigated during chronic bed rest (BR) and compared with that of acute supine conditions. The hypothesis was tested that 6 degrees head-down BR leads to hypovolemia, which activates antinatriuretic mechanisms so that the renal responses to standardized saline loading are attenuated. Isotonic (20 ml/kg body wt) and hypertonic (2.5%, 7.2 ml/kg body wt) infusions were performed in eight subjects over 20 min following 7 and 10 days, respectively, of BR during constant sodium intake (200 meq/day). BR decreased body weight (83.0 +/- 4.8 to 81.8 +/- 4.4 kg) and increased plasma osmolality (285.9 +/- 0.6 to 288.5 +/- 0.9 mosmol/kgH(2)O, P < 0.05). Plasma ANG II doubled (4.2 +/- 1.2 to 8.8 +/- 1.8 pg/ml), whereas other endocrine variables decreased: plasma atrial natriuretic peptide (42 +/- 3 to 24 +/- 3 pg/ml), urinary urodilatin excretion rate (4.5 +/- 0.3 to 3.2 +/- 0.1 pg/min), and plasma vasopressin (1.7 +/- 0.3 to 0.8 +/- 0.2 pg/ml, P < 0.05). During BR, the natriuretic response to the isotonic saline infusion was augmented (39 +/- 8 vs. 18 +/- 6 meq sodium/350 min), whereas the response to hypertonic saline was unaltered (32 +/- 8 vs. 29 +/- 5 meq/350 min, P < 0.05). In conclusion, BR elicits antinatriuretic endocrine signals, but it does not attenuate the renal natriuretic response to saline stimuli in men; on the contrary, the response to isotonic saline is augmented.