Aquaporin-2 downregulation in kidney medulla of aging rats is posttranscriptional and is abolished by water deprivation.

Aging kidney is associated in humans and rodents with polyuria and reduced urine concentrating ability. In senescent female WAG/Rij rats, this defect is independent of arginine-vasopressin (AVP)/V(2) receptor/cAMP pathway. It has been attributed to underexpression and mistargeting of aquaporin-2 (AQP2) water channel in the inner medullary collecting duct (IMCD). We showed previously that dDAVP administration could partially correct this defect. Since AQP2 can also be regulated by AVP-independent pathways in water deprivation (WD), we investigated AQP2 and phosphorylated AQP2 (p-AQP2) regulation in thirsted adult (10 mo old) and senescent (30 mo old) female WAG/Rij rats. Following 2-day WD, urine flow rate decreased and urine osmolality increased in both groups. However, in agreement with significantly lower cortico-papillary osmotic gradient with aging, urine osmolality remained lower in senescent animals. WD induced sixfold increase of plasma AVP in all animals which, interestingly, did not result in higher papillary cAMP level. Following WD, AQP2 and p-AQP2 expression increased hugely in 10- and 30-mo-old rats and their mistargeting in old animals was corrected. Moreover, the age-related difference in AQP2 regulation was abolished after WD. To further investigate the mechanism of AQP2 underexpression with aging, AQP2 mRNA was quantified by real-time RT-PCR. In the outer medulla, preservation of AQP2 protein expression was achieved through increased AQP2 mRNA level in senescent rats. In the IMCD, no change in AQP2 mRNA was detected with aging but AQP2 protein expression was markedly lower in 30-mo-old animals. In conclusion, there is a posttranscriptional downregulation of AQP2 with aging, which is abolished by WD.

[Aging and circadian clock gene expression in peripheral tissues in rats]. / Vieillissement et expression des gènes de l'horloge circadienne dans les tissus périphériques chez le rat.

Aging is associated with alterations of the circadian rhythms (shortened amplitude and phase-advance). We studied by quantitative RT-PCR the influence of aging on the expression of circadian clock genes (Clock, Bmal1, Cry1,2, Per1-3) in peripheral tissues (liver and heart) of middle-aged (13 months) and old (27 months) rats of the Wag/Rij strain exposed to a 12 hours light/12 hours dark cycle. Rats were killed at the light-dark transition (8 am and 8 pm). In the liver, Per, Cry et Bmal1 genes showed a morning/evening difference of expression; in addition, old rats exhibited a significant decrease of Per gene expression in the evening vs middle-aged rats. The heart showed similar profiles with only a tendency toward a decrease of Per expression and an increased Bmal1 expression in the evening in old rats. These results show that aging is associated with circadian gene expression changes.

Urea transporter expression in aging kidney and brain during dehydration.

Aging is commonly associated with defective urine-concentrating ability. The present study examined how the kidney and the brain of senescent (30-mo-old) female WAG/Rij rats respond to dehydration induced by 2 days of water deprivation in terms of urea transporter (UT) regulation. In euhydrated situation, senescent rats exhibited similar vasopressin plasma level but lower urine osmolality and papillary urea concentration and markedly reduced kidney UT-A1, UT-A3, and UT-B1 abundances compared with adult (10-mo-old) rats. Senescent rats responded to dehydration similarly to adult rats by a sixfold increase in vasopressin plasma level. Their papillary urea concentration was doubled, without, however, attaining that of dehydrated adult rats. Such an enhanced papillary urea sequestration occurred with a great fall of both UT-A1 and UT-A3 abundances in the tip of inner medulla and an increased UT-A1 abundance in the base of inner medulla. UT-A2 and UT-B1 were unchanged. These data suggest that the inability of control and thirsted senescent rats to concentrate urine as much as their younger counterparts derives from lower papillary urea concentration. In aging brain, UT-B1 abundance was increased twofold together with a fourfold increase in aquaporin-4 abundance. Dehydration did not alter the abundance of these transporters.

Food restriction prevents age-related polyuria by vasopressin-dependent recruitment of aquaporin-2.

The mechanisms underlying the prevention of age-related polyuria by chronic food restriction were investigated in female WAG/Rij rats. The decreased osmolality of renal papilla observed in senescent rats was not corrected by food restriction. A reduced urea content in the inner medulla of senescent rats, fed ad libitum or food-restricted, was suggested by the marked decrease in expression of UT-A1 and UT-B1 urea transporters. Aquaporin-2 (AQP2) downregulation in the inner medulla of senescent rats was partially prevented by food restriction. Both AQP2 and the phosphorylated form of AQP2 (p-AQP2), the presence of which was diffuse within the cytoplasm of collecting duct principal cells in normally fed senescent rats, were preferentially targeted at the apical region of the cells in food-restricted senescent animals. Plasma vasopressin (AVP) was similar in 10- and 30-mo-old rats fed ad libitum, but was doubled in food-restricted 30-mo-old rats. This study indicates that 1) kidney aging is associated with a marked decrease in AQP2, UT-A1, and UT-B1 expression in the inner medulla and a reduced papillary osmolality; and 2) the prevention of age-related polyuria by chronic food restriction occurs through an improved recruitment of AQP2 and p-AQP2 to the apical membrane in inner medulla principal cells, permitted by increased plasma AVP concentration.

Oromucosal interferon therapy: relationship between antiviral activity and viral load.

Intraperitoneal (i.p.) administration of 20,000 IU recombinant murine IFN-alpha (rMuIFN-alpha) was highly effective in protecting mice challenged i.p. with doses of encephalomyocarditis virus (EMCV) ranging from 44 to 440 LD(50) (p<0.001). Oromucosal (o.m.) IFN therapy was also found to be effective in protecting mice challenged with a lethal dose of EMCV. Thus, 40% of animals infected with 44 LD(50) of EMCV and treated o.m. with 20,000 IU rMuIFN-alpha survived infection with a mean survival time of 12.0 +/- 2.46 days relative to a mean of 6.11 +/- 0.38 days in the control group (p<0.05). Oromucosal IFN therapy was found to be ineffective, however, in animals infected with higher doses of EMCV (88-440 LD(50)), even though intraperitoneal administration of the same dose of rMuIFN-alpha resulted in the survival of 90%, 50%, and 60% of animals infected with 88, 220, and 440 LD(50) of EMCV, respectively. These results suggest that oromucosal IFN therapy is effective at relatively low viral load only and that the mechanism of action of oromucosal IFN therapy may be different from that of parenterally administered IFN. Our results suggest that oromucosal IFN therapy may be most effective in chronic viral infections as an alternative to parenterally administered IFN, which is clinically effective but poorly tolerated.

Sympathovagal balance is major determinant of short-term blood pressure variability in healthy subjects.

Short-term blood pressure variability (BPV) has been suggested to provide important information about cardiovascular regulation. However, the background of BPV, its determinants, and physiological correlates have remained obscure. The aim of this study was to characterize physiological correlates of BPV and to investigate associations between BPV and neural and hormonal regulatory systems at rest in healthy subjects. We studied 117 healthy, normal-weight, nonsmoking male and female subjects aged 23-77 yr. Spectral analysis of BPV and heart rate variability (HRV) was performed from 5-min blood pressure (Finapres) and electrocardiogram recordings during controlled breathing. Baroreflex sensitivity (BRS) was measured using the phenylephrine method. In addition, plasma concentrations of norepinephrine, epinephrine, and arginine vasopressin and plasma renin activity were measured. We found that the ratio between the low- and high-frequency components of HRV, an index of cardiac sympathovagal balance, correlated positively with total power and very low- and low-frequency components of systolic and diastolic BPV and inversely with high-frequency components of systolic and diastolic BPV. BRS, predominantly a measure of cardiac vagal regulation, correlated inversely with BPV. Furthermore, age, gender, body mass index, and systolic blood pressure contributed to BPV. Vasoactive hormones were not significant correlates of BPV. We conclude that sympathovagal balance of cardiovascular regulation is the major determinant of BPV. Other factors associated with BPV are age, gender, body mass index, blood pressure, and BRS.

Plasma volume expansion with oral fluids in hypohydrated men at rest and during exercise.

BACKGROUND: The purpose for this study was to evaluate various carbohydrate (CHO)-electrolyte fluid formulations for consumption by astronauts to maintain or restore their plasma volume (PV) and total body water (TBW) during and after extravehicular activity (exercise experiment, EE) and for a few hours before reentry and immediately after landing (rest experiment RE). HYPOTHESIS: That fluid formulation electrolyte content would be more important than osmotic (Osm) content for increasing or maintaining PV during the RE and EE. METHODS: In the RE, 5 healthy men (23-44 yr), previously dehydrated for 24 h, drank 6 fluid formulations (Water, 19.6 Na, 157 Na, 19.6 Na + glucose, and the prepared drinks Performances and Power)--one each at weekly intervals, and then sat for 70 min. In the EE, four healthy 24-h dehydrated men (30-46 yr) exercised for 70 min supine on a cycle ergometer (load = 71 +/- 1% peak VO2). RESULTS: Rest: Subjects who consumed formulations with total Osm concentrations nearer the normal range (157 Na - 270 mOsm x kg(-1), Performance with 19.6 mEq x L(-1) Na - 380 mOsm, and to some extent Power with 23.5 mEq x L(-1) Na - 390 mOsm) had the greater increases in PV; intake of drink 157 Na, with the largest Na content, induced the greatest hypervolemia of 7.6% (p < 0.05). The various additional ions, in addition to 19.6 Na, probably contributed to the 4.6% (p < 0.05) hypervolemia with Performance. Water was not effective. Exercise: Stabilization of PV between 15-70 min was not related to drink total CHO, Na or Osm content. Performance and 157 Na were no more effective than 19.6 Na or 19.6 Na + glu for PV stabilization. Water was the least effective. Regulatory mechanisms controlling PV during exercise appear to be independent of oral fluid formulation Osm-electrolyte content. CONCLUSIONS: Drink cation (sodium) content is more important that its total osmotic content for increasing plasma volume at rest. Fluid formulations with greater hypervolemic action in resting subjects may not be as effective during exercise; therefore different formulations for use during exercise appear to be necessary.

Mohs micrographic surgery for an erosive adenomatosis of the nipple.

BACKGROUND: Erosive adenomatosis of the nipple is a rare but distinct benign tumor of the nipple. It is usually considered to be derived from the apocrine sweat ducts of the nipple epithelium but probably of lactiferous duct origin. Total excision is the treatment of choice. OBJECTIVE: We report the clinical and histological features of this rare tumor, and the surgical technique employed. METHODS: Treatment consisted of Mohs micrographic surgery (MMS), fresh tissue technique, followed by primary closure. RESULTS: The described procedure resulted in a cure of the erosive adenomatosis of the nipple. CONCLUSION: Total excision of erosive adenomatosis of the nipple can be obtained by MMS. This technique prevents recurrence of the disease and minimizes resulting deformation of this important anatomic area.

Age and gender dependency of baroreflex sensitivity in healthy subjects.

We evaluated the correlates of baroreflex sensitivity (BRS) in healthy subjects. The study consisted of 117 healthy, normal-weight, nonsmoking male and female subjects aged 23-77 yr. Baroreflex control of heart rate was measured by using the phenylephrine bolus-injection technique. Frequency- and time-domain analysis of heart rate variability and an exercise test were performed. Plasma norepinephrine, epinephrine, insulin, and arginine vasopressin concentrations and plasma renin activity were measured. In the univariate analysis, BRS correlated with age (r = -0.65, P < 0.001), diastolic blood pressure (r = -0.47, P < 0.001), exercise capacity (r = 0.60, P < 0.001), and the high-frequency component of heart rate variability (r = 0.64, P < 0.001). There was also a significant correlation between BRS and plasma norepinephrine concentration (r = -0.22, P < 0.05) and plasma renin activity (r = 0.32, P < 0.001). According to the multivariate analysis, age and gender were the most important physiological correlates of BRS. They accounted for 52% of interindividual BRS variation. In addition, diastolic blood pressure and high-frequency component of heart rate variability were significant independent correlates of BRS. BRS was significantly higher in men than in women (15.0 +/- 1.2 vs. 10.2 +/- 1.1 ms/mmHg, respectively; P < 0.01). Twenty-four percent of women > 40 yr old and 18% of men > 60 yr old had markedly depressed BRS (< 3 ms/mmHg). We conclude that physiological factors, particularly age and gender, have significant impact on BRS in healthy subjects. In addition, we demonstrate that BRS values that have been proposed to be useful in identifying postinfarction patients at high risk of sudden death are frequently found in healthy subjects.

Drinking-induced plasma vasopressin and norepinephrine changes in dehydrated humans.

After 24-h water deprivation, five men (23-41 yr; 78 +/- 3.6 kg) consumed, within 4.0-6.2 min, 12 mL/kg of one of six fluid formulations (16.5 C) once a week over a period of 6 weeks: water, hypotonic saline (0.045% Na+), isotonic saline (0.36% Na+), hypertonic glucose (9.7% glucose), and two commercial mildly hypertonic 9.7% carbohydrate drinks. Blood samples were drawn 5 min before and 3, 9, 15, 30, and 70 min after completion of drinking. Ingestion induced no significant change in plasma Na+, K+, osmotic, or protein concentrations; blood pressure; or heart rate. Plasma volume (PV) was increased (P < 0.05) between 30-70 min with isotonic saline and the two commercial drinks. Ingestion induced a decrease in plasma AVP (PAVP) at 3 min, which was maximal (P < 0.05) at 15 min with all drinks. Thus, the act of drinking, independent of the composition or osmolality of the fluid absorbed, leads to a prompt inhibition of PAVP secretion in man. With the exception of rehydration with isotonic saline, this prompt response was followed by a long lasting inhibition of PAVP. There was no change in PRA, plasma aldosterone, atrial natriuretic peptide, or epinephrine, but an increase in plasma norepinephrine occurred immediately after ingestion, which suggests, like that for PAVP depression, a drinking-stimulated neural mechanism.

Central cardiovascular effects of acetylcholine in the conscious dog.

1. The effects of central cholinomimetic drugs on cardiovascular and vasoactive hormonal responses (blood pressure, heart rate, catecholamines, vasopressin, atrial natriuretic factor, neuropeptide Y plasma levels and plasma renin activity) were investigated in conscious Beagle dogs. For this purpose a catheter was chronically implanted into each dog's cisterna magna to allow repeated central injections in the awake animals. 2. Intracisternal acetylcholine (20 micrograms kg-1) significantly increased systolic and diastolic blood pressure. These changes were accompanied by an initial short term tachycardia followed by a long lasting bradycardia. Intracisternal acetylcholine also increased noradrenaline, adrenaline and vasopressin plasma levels, decreased plasma renin activity but did not modify plasma levels of neuropeptide Y and atrial natriuretic factor. 3. The effects of acetylcholine were completely abolished by pretreatment with intracisternal injection of the muscarinic antagonist, atropine (5 micrograms kg-1) but not by the intracisternal injection of the nicotinic antagonist, mecamylamine (25 micrograms kg-1). 4. The present results demonstrate that there are qualitative and quantitative differences between the central cardiovascular effects of acetylcholine in conscious dogs compared to what we previously reported, using a comparable protocol, in anaesthetized dogs. Under both conditions, we observed a central cholinergically mediated increase in blood pressure secondary to an increase in sympathetic tone and vasopressin release but these responses were shorter (less than 10 min) in the conscious dogs than in anaesthetized dogs (more than 10 min). Moreover, we detected in the response to the central cholinergic stimulation in the conscious dogs a significant increase in plasma adrenaline levels and biphasic changes in heart rate which were not described previously in the anaesthetized dog.

Physiological correlates of attenuated salt appetite in Fischer 344 rats.

Dietary NaCl deprivation stimulates a robust salt appetite in Wistar rats but has little influence on this behavior in rats of the Fischer 344 (F344) strain. To examine physiological substrates of attenuated salt appetite in F344 rats, several pertinent measures of renal function and fluid homeostasis were made in Wistar and F344 rats eating normal and NaCl-deplete diets. Physiological adjustments to NaCl deprivation were similar between the two strains; however, F344 rats showed smaller increases in plasma renin activity (PRA) than their Wistar counterparts. In addition, F344s decreased urinary sodium excretion more rapidly than Wistar rats in response to deprivation. The present studies also revealed several strain differences in baseline fluid and electrolyte regulation. Relative to the Wistar strain, F344 rats were characterized by high baseline PRA, increased arginine vasopressin (AVP) excretion, decreased urine volume, and diminished thirst. We propose that AVP and oxytocin activation may reduce salt preference and suppress the development of salt appetite in F344 rats.

Renal and systemic adaptation to sodium restriction in aging rats.

The influence of age on the systemic and renal adaptation to dietary sodium restriction was assessed in 10-, 20-, and 30-mo-old female WAG/Rij rats. In control conditions, mean arterial pressure (MAP) was similar in all rats and plasma renin activity (PRA) was lower in 30- than in 10- and 20-mo-old rats (2.5 +/- 0.6, 5.1 +/- 0.4, and 3.9 +/- 1.0 ng ANG I.ml-1.h-1, respectively). Dietary sodium restriction was associated with a reduction in MAP in 30-mo-old rats, whereas no change occurred in 10- and 20-mo-old rats. Impairment in the early (days 1-6) renal adaptation to salt restriction was observed in 30- compared with 10- and 20-mo-old rats (6-day cumulative sodium excretion of 728 +/- 139, 437 +/- 53, and 478 +/- 37 mumol, respectively). During the 7- to 12-day period, MAP stabilized in the oldest rats and cumulative sodium excretion became similar to that of other age groups. The early increase in PRA and urinary aldosterone excretion observed in 10- and 20-mo-old rats was consistently blunted in 30-mo-old rats. These findings suggest that the delayed response of the renin-angiotensin-aldosterone system has a major role in the impaired renal and systemic adaptation to dietary sodium removal in senescent rats.

Orthostasis: exercise and exercise training.

There are two major problems here that are not independent. One is the more practically oriented problem of determining the effect of various modes of exercise training on gravitational tolerances, i.e., the point of syncope (unconsciousness) usually estimated from the time of appearance of presyncopal signs and symptoms. The other is more theoretical and concerns the mechanism of blood pressure failure that results in syncope. In many experimental designs these two problems or purposes have been intermingled, with equivocal results.

Relationship between vasopressin and renal concentrating ability in aging rats.

The relationship between arginine vasopressin (AVP) secretion and the age-related change in renal concentrating ability was studied in 10-, 20-, and 30-mo-old conscious rats. In control condition, urine osmolality (Uosmol) was 2,358 +/- 99, 1,919 +/- 87, and 1,135 +/- 173 mosmol/kgH2O (mean +/- SE) and the corresponding plasma AVP concentration 3.1 +/- 1.2, 2.8 +/- 0.7, and 3.3 +/- 0.7 pg/ml at 10, 20, and 30 mo. Urinary AVP excretion and AVP content in the hypothalamus were comparable in the 3 age groups, while the basal AVP pituitary content was significantly higher at 10 than at 20 or 30 mo. Three days of dehydration induced 1) a similar increase in plasma concentration and urinary excretion of AVP in the 3 groups, even though the maximal Uosmol reached by the oldest animals was significantly reduced (3,988 +/- 218, 3,652 +/- 273, and 2,826 +/- 197 mosmol/kgH2O at 10, 20, and 30 mo, respectively) and 2) a similar AVP depletion of the pituitary at 10, 20, and 30 mo and an increase of the AVP content in the hypothalamus at 10 mo but not at 20 and 30 mo. These results suggest that the decrease in renal concentrating ability reported in aging rats is not due to an inappropriate secretion of AVP along the hypothalamo-neurohypophysial axis but is rather related to an impaired responsiveness of the kidney to the antidiuretic hormone.

Plasma vasopressin and cortical nephron function in aging rats.

The role of vasopressin and Henle's loop transport in age-related polyuria and decrease in urine osmolality was investigated in female WAG/Rij rats free of kidney disease. In these animals, urine osmolality dropped from 2000 mosmol/kg H2O to 1000-1200 mosmol/kg H2O between 10 and 30 months, and urinary volume increased in proportion. Vasopressin concentration measured in plasma withdrawn from conscious, unrestrained, chronically catheterized rats was not significantly different in 10, 20 and 30-month-old animals (mean values 2.5 +/- 0.7, 2.2 +/- 0.2 and 2.0 +/- 0.3 pg/ml (n = 8), respectively). This suggests an impaired responsiveness of old kidney to antidiuretic hormone. The possible involvement of Henle's loop in this defect was studied by micropuncture. Paired collections of tubular fluid were done in the early distal and late proximal convolutions of the same cortical nephrons. Single nephron filtration rates did not significantly differ with age. Tubular fluid osmolalities in the early distal convolution were 165 +/- 13, 178 +/- 9 and 160 +/- 11 (n = 14) mosmol/kg H2O in 10-, 20- and 30-month-old rats, indicating similar diluting capacity of the cortical thick ascending limb. The amount of sodium transported from lumen to peritubular space by Henle's loop was also unchanged with age as were water, calcium, magnesium and potassium reabsorptions. These data indicate that the age-related decrease in urine osmolality is not related to either a significant reduced vasopressin plasma concentration or an increased single glomerular filtration rate or a reduced transport capacity of Henle's loop of the cortical nephron. Rather they suggest an impaired response to vasopressin of other segments of the nephron that is, the medullary thick ascending limb of Henle's loop and/or the collecting duct.

Effects of blood sampling, anesthesia and surgery on plasma vasopressin concentration in rats.

The influence of blood sampling, anesthesia and surgery on plasma vasopressin concentration was assessed in rats. Mean plasma concentration in conscious, chronically catheterized rats was 1.4 +/- 0.1 pg/ml (n = 6). This value remained constant over repeated plasma samplings in the same animals. On the other hand, decapitation increased the plasma vasopressin concentration to 6.0 +/- 2.4 (in pg/ml) (n = 6), inactin anesthesia to 2.9 +/- 0.6 (n = 6), anesthesia and femoral cannulation to 13.3 +/- 5.8 (n = 6) and surgery for renal micropuncture to 81.3 +/- 35.0 (n = 6). It is concluded that the level of circulating plasma vasopressin is highly dependent on the sampling technique and is closely related to the extent of surgery.

Hemodynamic and hormonal effects of prolonged anti-G suit inflation in humans.

This study examined the hemodynamic consequences of prolonged lower body positive-pressure application and their relationship to changes in the plasma concentration of the major vasoactive hormones. Six men [36 +/- 2 (SE) yr] underwent 30 min of sitting and then 3 h of 70 degrees head-up tilt. An antigravity suit was applied (60 Torr legs, 30 Torr abdomen) during the last 2 h of tilt. In a similar noninflation experiment, the endocrine responses were measured in the suited subjects tilted for 3 h. Two-dimensional echocardiography was used to calculate ventricular volume and cardiac output. Measurements were made 30 min before and 30 and 90 min after inflation. Immediately after inflation, mean arterial pressure increased by 7 +/- 2 Torr and heart rate decreased by 16 +/- 4 beats/min. Left ventricular end-diastolic volume and systolic volume increased significantly (P less than 0.05) at 30 and 90 min of inflation. Cardiac output increased after 30 min of inflation and returned to the preinflation level at 90 min. Plasma norepinephrine and plasma renin activity were maximally suppressed after 15 and 90 min of inflation, respectively (P less than 0.05). No such hormonal changes occurred during control. Plasma sodium, potassium, and osmolality remained unchanged during both experiments. Thus, prolonged application of lower body positive pressure induces 1) a transient increase in cardiac output and 2) a marked and sustained decrease in plasma norepinephrine and plasma renin activity, which reflect an inflation-induced decrease in sympathetic activity.

Plasma atrial natriuretic peptide and vasopressin during thermal dehydration in supine posture.

After 30 minutes spent in an upright posture six healthy male subjects underwent two 130-minute experiments in a supine posture, the first in thermoneutral conditions (TC) and the second, 15 days later, in a hot environment (HE) in order to obtain a water loss of 2.5% body weight. In thermoneutral conditions, the supine posture induced plasma volume expansion, resulting in slightly lowered plasma vasopressin (AVP) levels and higher plasma atrial natriuretic peptide (ANP) levels, compared to the values obtained in the upright posture (P less than 0.05). During hot environment, the sweating-induced dehydration led to a significant reduction of plasma volume expansion and to an increase in rectal temperature and plasma osmolality (P less than 0.05). Plasma vasopressin levels were higher at the end of the heat exposure (P less than 0.05) but natriuretic peptide levels did not change, compared to the values observed in the upright posture. These data suggest that plasma volume reduction induced by thermal dehydration may limit the natriuretic peptide release, which occurs after changing from the upright to a supine position.

Effects of acute exercise and prolonged exercise training on blood pressure, vasopressin and plasma renin activity in spontaneously hypertensive rats.

The purpose of this study was to investigate the effect of swimming training on systolic blood pressure (BPs), plasma and brain vasopressin (AVP), and plasma renin activity (PRA) in spontaneously hypertensive rats (SHR) during rest and after exercise. Resting and postexercise heart rate, as well as blood parameters such as packed cell volume (PCV), haemoglobin concentration (Hb), plasma sodium and potassium concentrations ([Na+], [K+]) osmolality and proteins were also studied. Hypophyseal AVP had reduced significantly after exercise in the SHR, whereas PRA had increased significantly in the Wistar-Kyoto (WKY) strain used as normotensive controls. Plasma AVP concentration increased in both strains. By the end of the experiment, training had reduced body mass and BPs by only 10% and 6%, respectively. Maximal oxygen uptake was increased 10% and plasma osmolality 2% by training. The postexercise elevation of heart rate was not significantly attenuated by training. A statistically significant reduction in postexercise plasma osmolality (10%) and [Na+] (4%) was observed. These results suggested that swimming training reduced BPs. Plasma and brain AVP played a small role in the hypertensive process of SHR in basal conditions because changes in AVP contents did not correlate with those of BPs. Moreover, there were no differences between SHR and WKY in plasma, hypophyseal and hypothalamic AVP content in these basal conditions. Finally, during moderate exercise a haemodilution probably occurred with an increase of plasma protein content. This was confirmed by the exercise-induced increase of plasma AVP and the reduction of hypophyseal AVP content, suggesting a release of this hormone, which probably contributed to the water retention and haemodilution.(ABSTRACT TRUNCATED AT 250 WORDS)