Plasma Electrolyte Concentrations Research Articles

Haemodialysis increases QT(c) interval but not QT(c) dispersion in ESRD patients without manifest cardiac disease.

HD has been reported to determine an increase in QTc interval and QTc dispersion (QT(max)-QT(min))-risk factors that predispose to severe ventricular arrhythmias and sudden death. However, most studies have included end-stage renal disease (ESRD) patients with significant heart pathology. We therefore aimed to study the impact of a single HD session in subjects without manifest cardiac disease. Sixty-eight stable, non-diabetic HD patients (47.1% males, age 40.2+/-12.7 years, HD duration 57+/-36 months and 37% hypertensive), with normal maximal ECG stress test and sub-endocardiac viability index and without ECG left ventricular hypertrophy were included. QT interval was calculated 10 min pre- and post-HD, as an average of three consecutive complexes, and corrected for heart rate using Bazett's formula (QTc=QT/(R-R)(1/2)). Na(+), K(+), Ca(2+), PO(4), pH and BP levels were also determined pre- and post-HD. The QTc interval increased significantly post-HD to 434+/-29 from 421+/-26 ms pre-HD (P=0.005); an abnormally prolonged QTc (>440 ms) was recorded in 34% cases pre-HD and in 46% post-HD, i.e. 1.5-2.3 times higher than in the high risk EURODIAB IDDM population. However, this effect was not homogeneous. Only 47 subjects had an increase in QTc duration after a dialysis session, while in 21 a decrease in QTc duration was recorded. The increase in QTc post-HD correlated with Ca(2+) homeostasis. Patients with greater increases in QTc after dialysis had higher baseline plasma calcium levels (r=0.47, P<0.001); also, a larger decrease in Ca(2+) post-HD correlated with higher increases in QTc interval (r=0.33, P<0.05). In contrast with QTc behaviour and with data from the literature, in this young HD population without manifest cardiac disease and with a low prevalence of HTA, post-HD QTc dispersion was similar to pre-HD values, increasing in only 39 patients. Furthermore, changes in QTc dispersion were not related to changes in electrolytes and BP following dialysis. However, changes in QTc dispersion and in QTc interval were directly correlated (r=0.37, P=0.42). There were no relationships between pre-HD measured echocardiographic variables, including: LV ejection fraction, internal diameters, wall thickness, mass and mass index and baseline or changes in QTc or QTc-d. Haemodialysis increases the QTc interval in ESRD patients, mainly related to rapid changes in electrolyte plasma concentrations. However, the impact on QTc dispersion is less important in the absence of significant coexisting cardiac disease.

Plasma aldosterone concentration and renal sodium excretion are altered during the first days of training.

The purpose of the present study was to determine whether the training-induced hypervolaemic response seen in the horse is associated with aldosterone-mediated renal mechanisms affecting sodium conservation during the first days of training. Five healthy, Standardbred mares (weight 450-500 kg, age 4-8 years) that were unfit, but accustomed to running on the treadmill, were used to test the hypothesis that repeated submaximal exercise would alter plasma aldosterone (ALDO) concentration and renal excretion of electrolytes in horses within the first 3 days of training. The experiment consisted of a 2 week housing equilibration period followed by a 1 week control period and a 3 day exercise training period (30 min/day at 60% VO2max). During control, ALDO and renal fluid and electrolyte losses were measured for 24 h on 3 separate days. Renal function (urine volume [UV], 24 h excretion of Na+, K+ and Cl- [UNA+ V, UK+ V, UCl- V], clearance of Na+ [CNa+], K+ [CK+] and Cl- [CCl-], creatinine [CCr], osmotic substances [Cosm], and solute-free water [FWC], and the fractional excretion of Na+, K+ and Cl-) and ALDO were measured for an additional 3 consecutive days during the training period. There were no differences (P>0.05) in any variable during the control period. Plasma volume increased (+18.7%, P<0.05) after 3 days of training. During training, there were no significant changes in plasma osmolality, electrolyte concentrations or CCr. Training caused decreases (P<0.05) in UV (-30%), UNA+ V (-73%), UK+ V, (-55%) and UCl- V (-70%). Training also caused decreases (P<0.05) in Cosm (-30%), through decreases in CNa+ (-60%), CK+ (-60%), and CCl- (-66%). Interestingly, FWC increased (+30%, P<0.05), whereas, there were significant decreases in the fractional excretion of Na+ (-59%), K+ (-48%) and Cl- (-60%). Training caused substantial elevations in both pre-exercise (967%, P<0.05) and postexercise (+3013%, P<0.05) plasma ALDO concentrations suggesting an increase in both basal levels and the responsiveness to acute exercise. Together, these observations suggest that mechanisms affecting tubular conservation of electrolytes contribute to the early response to training. However, it is also concluded that renal mechanisms appear to be only part of the mechanism for conserving sodium and water intake as well as training-induced changes in gastrointestinal mechanisms affecting electrolyte and water balance.

Plasma and urine electrolyte and mineral concentrations in Thoroughbred horses with recurrent exertional rhabdomyolysis after consumption of diets varying in cation-anion balance.

To determine whether plasma, urine, and fecal electrolyte and mineral concentrations differ between clinically normal horses and Thoroughbreds with recurrent exertional rhabdomyolysis (RER) after consumption of diets varying in cation-anion balance. 5 Thoroughbred mares with RER and 6 clinically normal mixed-breed mares. Each of 3 isocaloric diets designated as low, medium, and high on the basis of dietary cation-anion balance (DCAB) values of 85, 190, and 380, respectively, were fed to horses for 14 days. During the last 72 hours, 3 horses with RER and 3 control horses had daily urine and fecal samples obtained by total 24-hour collection. Remaining horses had urine samples collected daily by single catheterization. For each diet, no differences existed between horses with RER and control horses in plasma pH, electrolyte concentrations, and creatine kinase activity or in urine pH and renal fractional excretion (FE) values. Plasma pH, strong ion difference, bicarbonate and total carbon dioxide concentrations, and base excess decreased and plasma chloride and ionized calcium concentrations increased with decreasing DCAB. Urine pH decreased with decreasing DCAB. The FE of chloride and phosphorus were greatest for horses fed the low diet. The FE values for all electrolytes exept magnesium did not differ between urine samples obtained by single catheterization and total 24-hour collection. Daily balance of calcium, phosphorus, sodium, chloride, and potassium did not differ significantly among horses fed the various diets. In clinically normal horses and in horses with RER, the DCAB strongly affects plasma and urine pH and the FE of sodium, potassium, chloride, and phosphorus.

Susceptibility of rainbow trout Oncorhynchus mykiss, Atlantic salmon Salmo salar and coho salmon Oncorhynchus kisutch to experimental infection with sea lice Lepeophtheirus salmonis.

Physiological, immunological and biochemical parameters of blood and mucus, as well as skin histology, were compared in 3 salmonid species (rainbow trout Oncorhynchus mykiss, Atlantic salmon Salmo salar and coho salmon O. kisutch) following experimental infection with sea lice Lepeophtheirus salmonis. The 3 salmonid species were cohabited in order to standardize initial infection conditions. Lice density was significantly reduced on coho salmon within 7 to 14 d, while lice persisted in higher numbers on rainbow trout and Atlantic salmon. Lice matured more slowly on coho salmon than on the other 2 species, and maturation was slightly slower on rainbow trout than on Atlantic salmon. Head kidney macrophages from infected Atlantic salmon had diminished respiratory burst and phagocytic capacity at 14 and 21 d post-infection (dpi), while infected rainbow trout macrophages had reduced respiratory burst and phagocytic capacities at 21 dpi, compared to controls. The slower development of lice, coupled with delayed suppression of immune parameters, suggests that rainbow trout are slightly more resistant to lice than Atlantic salmon. Infected rainbow trout and Atlantic salmon showed increases in mucus lysozyme activities at 1 dpi, which decreased over the rest of the study. Mucus lysozyme activities of infected rainbow trout, however, remained higher than controls over the entire period. Coho salmon lysozyme activities did not increase in infected fish until 21 dpi. Mucus alkaline phosphatase levels were also higher in infected Atlantic salmon compared to controls at 3 and 21 dpi. Low molecular weight (LMW) proteases increased in infected rainbow trout and Atlantic salmon between 14 and 21 dpi. Histological analysis of the outer epithelium revealed mucus cell hypertrophy in rainbow trout and Atlantic salmon following infection. Plasma cortisol, glucose, electrolyte and protein concentrations and hematocrit all remained within physiological limits for each species, with no differences occurring between infected and control fish. Our results demonstrate that significant differences in mucus biochemistry and numbers of L. salmonis occur between these species.

Additive effects of a sodium chloride restricted diet and furosemide administration in healthy dogs.

To determine the effects of a low or high sodium (Na) diet with or without furosemide administration on plasma electrolyte concentrations and the renin-angiotensin-aldosterone system in healthy dogs. 20 healthy adult dogs. Dogs were randomly allotted to 4 groups of 5 dogs each as follows: dogs fed a low Na diet (0.08% Na and 0.8% chloride [CI] on a dry matter [DM] basis); dogs fed a low Na diet with added NaCl (1.0% Na and 2.2% Cl on a DM basis); dogs fed a low Na diet and treated with furosemide (2 mg/kg of body weight, PO, q 12 h); and dogs fed a low Na diet with added NaCl and treated with furosemide. Plasma electrolyte concentrations were measured on days 0, 21, and 35. Plasma renin activity and aldosterone concentration were analyzed by use of radioimmunoassays on days 0, 21, 35, and 53. Furosemide treatment significantly decreased plasma Cl concentration and significantly increased plasma renin activity and aldosterone concentration. Dogs fed a low Na diet had significantly higher plasma renin activities and plasma aldosterone concentrations. A significant interaction between a low Na diet and furosemide administration resulted in the lowest plasma Cl concentrations, highest plasma renin activities, and highest plasma aldosterone concentrations. In healthy dogs, feeding a low Na diet and administering furosemide resulted in an additive effect on plasma Cl concentration, renin activity, and aldosterone concentration, which may be an important consideration for treating dogs with cardiac disease.

Acute and Chronic Effects of Intravenous Hypertonic Saline Solution and Rehydration Fluid on Plasma Electrolyte Concentrations and Renal Function in Holstein Steers

Intravenous (IV) administration of 7.0-7.5% hypertonic saline solution (HSS) is commonly used in dehydrated dairy cows with endotoxic shock and endotoxemia associated with environmental mastitis. Cows are given an IV empirical dose of one to two liters ofHSS (4-5 ml/kg BW) followed by immediate access to drinking water and supportive therapy (anti-inflammatory drugs, oxytocin and frequent milk-out for mastitis). Intravenous small-volume HSS, in conjunction with voluntary oral water consumption, is purported to totally alleviate dehydration without the need for large-volume IV balanced replacement fluids. Use of HSS as the resuscitation fluid for hypovolemia associated with hemorrhagic shock or with loss of vascular tone, as in sepsis or neurogenic shock, remains controversial. HSS resuscitation may detrimentally affect renal function and survival when used in dehydrated patients. This study was conducted to determine detrimental effects on renal function using HSS as the resuscitation fluid in dehydrated cattle.

A method to estimate urinary electrolyte excretion in patients at risk for developing cerebral salt wasting.

Two major criteria are necessary to diagnose cerebral salt wasting (CSW): a cerebral lesion and a large urinary excretion of Na+ and Cl- at a time when the extracellular fluid (ECF) volume is contracted. Nevertheless, it is difficult for the physician to confirm from bedside observation that a patient has a contracted ECF volume. Hyponatremia, although frequently present, should not be a criterion for a diagnosis of salt wasting. A contracted ECF volume is unlikely if there are positive balances of Na+ and Cl-. The goal of this study was to assess the accuracy of calculating balances for Na+ plus K+ and of Cl- over 1 to 10 days in an intensive care unit (ICU) setting. A prospective comparison of measured and estimated quantities of Na+ plus K+ and of Cl- excreted over 1 to 10 days in 10 children and 12 adults who had recently received a traumatic brain injury or undergone recent neurosurgery. Plasma concentrations of electrolytes were recorded at the beginning and end of the study period. The total volumes infused and excreted and the concentrations of Na+, K+, and Cl- in the infusate were obtained from each patient's ICU chart. The electrolytes in the patients' urine were measured and calculated. Correlations between measured and calculated values for excretions of Cl- and of Na+ plus K+ were excellent. Mass balances for Na+ plus K+ and for Cl- can be accurately estimated. These data provide information to support or refute a clinical diagnosis of CSW. The danger of relying on balances for these electrolytes measured within a single day to diagnose CSW is illustrated.

Water drinking causes a biphasic change in blood composition in humans.

To investigate precisely the fluid shifts associated with water drinking in humans, we measured continuously blood density and plasma electrolyte concentrations using the mechanical oscillator technique and ion-selective electrodes, respectively, in healthy young volunteers before (10 min) and after (48 min) water drinking for a period of 2 min. Beat-by-beat blood pressure was also monitored throughout the experiment. Drinking 1 l tap water caused a transient increase in blood density immediately after the drinking episode (from 1051.1+/-0.5 g/l before drinking to 1051.8+/-0.5 g/l 4 min after the start of drinking, P<0.05), followed by a gradual reduction (1050.1+/-0.5 g/l at 31 min). This drinking-induced change paralleled those of haematocrit, plasma density and plasma volume. Plasma [Na+] and [Cl-] and osmolality decreased after drinking without transient increases and reached minima at about 30 min. A transient increase in mean arterial blood pressure was observed prior to the increase in blood density. These findings suggest that water drinking causes a biphasic change in plasma volume: initial haemoconcentration, probably due to sympathetic acceleration, followed by haemodilution due to the post-absorptive effect, and further suggest that the fluid shift associated with the initial haemoconcentration is isosmotic.

Circadian variation of plasma atrial natriuretic peptide, cortisol and fluid balance in the goat

Circadian variation of plasma atrial natriuretic peptide (ANP), cortisol and fluid balance was studied in ten adult female goats. The concentrations of plasma antidiuretic hormone (ADH), electrolytes, creatinine and total protein, as well as plasma and urine osmolalities and renal electrolyte excretion and clearances (Cosm, CH2O, Ccrea), were used to evaluate fluid balance. At 3-h intervals, urine was collected from five goats and venous blood samples from all ten goats. Urethral catheterization had no effect on the results. Besides the lower plasma creatinine level in the dark than in daylight, no other changes were observed in relation to luminousness. Plasma concentrations of ANP, ADH, total protein and K, urine flow rate and osmolality, urine concentrations of Na, K and creatinine, renal Na and K excretion, Cosm, CH2O and Ccrea, and haematocrit showed no circadian variation. Circadian variation was observed in plasma osmolality (P < 0.05) and the concentrations of Na (P < 0.05) and creatinine (P < 0.05), with achrophases around 16:00 hours and nadirs between 01:00 and 07:00 hours. Changes in osmolality and Na followed the feeding schedule. There was a small elevation in plasma cortisol levels in six goats after midnight, which may be the consequence of circadian rhythm. In conclusion, the results suggest that in plasma ANP no circadian rhythm exists.

Vasopressin V1a receptor antagonism does not reverse adrenocorticotrophin-induced hypertension in the rat.

1. The role of arginine vasopressin (AVP) was examined in adrenocorticotrophin (ACTH)-induced hypertension in Sprague-Dawley rats using the non-peptide AVP V1a receptor antagonist OPC 21268. 2. In an acute study, six rats were pretreated with ACTH for 11 days and direct arterial blood pressure (4 h), plasma osmolality and electrolyte concentrations were measured after OPC 21268 gavage. In a chronic study, 40 rats were randomly divided into four groups: (i) sham injection + sham gavage; (ii) ACTH + sham gavage; (iii) sham injection + OPC 21268; or (iv) ACTH + OPC-21268 for 16 days. Systolic blood pressure (SBP), water intake, urine volume (UV), urine osmolality and electrolytes, food intake, bodyweight and plasma osmolality and electrolyte concentrations were measured. 3. In the acute study, direct mean arterial blood pressure did not change with OPC 21268 (122+/-2 and 120+/-3 mmHg at 0 and 240 min, respectively). 4. In the chronic study, OPC 21268 did not affect ACTH-induced rises in blood pressure (from 125+/-2 (control) to 145+/-5 mmHg (group 4) compared with 122+/-3 (control) to 149+/-5 mmHg (group2)). Water intake and UV increased (from 29+/-2 to 83+/-6 mL/day; and from 5+/-1 to 36+/-5 mL/day, respectively) and the change in bodyweight decreased from 0+/-2 to -107+/-7 g. 5. These results suggest that AVP (at the V1a receptor) does not play a significant role in the maintenance of ACTH-induced hypertension.

Nutritional and physiological status of U.S. national figure skaters.

This study assessed the nutrient intake, body composition and biochemical indices of National Figure Skating Championship competitors. Four-day diet records, fasting blood samples, and anthropometric measurements were obtained 2 months after the National Championships from 41 figure skaters 11-18 years of age. Energy, carbohydrate, fat, dietary fiber and cholesterol intake were significantly lower compared to the NHANES III averages for adolescents in the U.S. In general, the mean intakes for most vitamins except vitamin D and E were above the recommended intake. But the athletes had lower intakes of vitamin E and B12, and higher intakes of vitamin C, and thiamin (females only) compared with NHANES III. The mean intakes of magnesium, zinc, and iodine by the male skaters were below the recommended levels, as were the mean intakes of calcium, iron, phosphorus, magnesium, and zinc by the female skaters. Also, the number of servings from vegetable, fruit, dairy, and meat groups were below the recommended levels. Biochemical indices of nutritional status were within normal limits for all skaters. But plasma electrolyte concentrations were indicative of potential dehydration status. The results suggest there is a need to develop dietary intervention and educational programs targeted at promoting optimal nutrient and fluid intakes by these athletes to maintain performance and improve long-term health status.

Effects of frusemide on electrolyte and acid-base balance during exercise.

This study was undertaken to evaluate the effects of frusemide on the concentration of plasma electrolytes and the relationship between changes in electrolyte concentration and the simultaneous changes in acid-base balance in arterial and venous blood during intense exercise. Five exercise-conditioned Thoroughbred horses were exercised on a high-speed treadmill at a slope of 10% at speeds known to exceed VO2max. Horses participated in 3 randomised exercise trials in which they received either placebo (control), low-dose frusemide (0.5 mg/kg bwt), or high-dose frusemide (1.0 mg/kg) 4 h prior to exercise. Arterial and mixed venous blood samples were drawn before, during and after intense exercise. Packed cell volume (PCV), plasma protein, plasma electrolyte, plasma lactate concentrations and acid-base balance were determined. Frusemide at both dosages induced a significant metabolic alkalosis associated with a decrease in plasma çhloride[ in both arterial and mixed venous blood. There was a highly significant correlation between the strong ion difference (SID) and bicarbonate[ in all blood samples. The effects of frusemide on electrolyte concentration and acid-base balance were largely due to changes in SID.

The effect of dietary fibre on hydration status after dehydration with frusemide.

Three diets were fed to 6 horses in a 3 x 6 Latin rectangle experiment to determine if dietary fibre could improve hydration status in response to dehydration with frusemide. Frusemide was used to simulate dehydration from exercise-induced sweat loss. Diets contained similar dry matter (DM), energy, protein and electrolyte content, but differed in total dietary fibre (TDF) and/or soluble fibre (SDF). The 3 diets were: 1) HIGH-HIGH (high TDF, high SDF); 2) HIGH-LOW (high TDF, low SDF); and 3) LOW-LOW (low TDF, low SDF). In each 10 day period, water intake and faecal moisture content were assessed on Day 7. On Day 10, feed and water were withheld and horses were dehydrated with frusemide (1 mg/kg bwt, i.m.). Plasma volume (PV), plasma total protein (TP), packed cell volume (PCV) and plasma electrolyte concentrations were determined before and after frusemide administration. Water consumption was greater (P < 0.05) when horses received diets high in TDF. Faecal moisture content was greatest (P < 0.01) when horses received the HIGH-HIGH diet. The decline in PV and the rise in plasma TP concentration following frusemide administration were similar for all diets. When horses received the HIGH-HIGH diet, they had a greater (P < 0.05) bodyweight before dehydration and lost more (P < 0.05) bodyweight in response to frusemide. A greater loss of bodyweight in response to frusemide without a proportional loss of PV when horses received the HIGH-HIGH diet suggests that a diet high in SDF may provide the horse with a source of dispensable water in the hind gut during dehydration.

Sodium bicarbonate and potassium bicarbonate supplements for broilers can cause poor performance at high temperatures

1. Supplements of between 2 and 8 g of sodium bicarbonate (NaHCO3)/l in drinking water provided between 21 and 49 d of age to broilers at 31 degress C increased growth after 35 d of age and food intake after 42 d of age compared to unsupplemented controls. The most consistent responses were observed with 2 g NaHCO3/l. 2. Differences in weekly water intakes with different concentrations of NaHCO3 in the drinking water did not equate with variations in weekly food intake and growth. 3. Unexpected high mortality from dehydration and nephrosis was observed with a 10 g NaHCO /l supplement. This mortality was associated with major changes in blood acid-base balance and plasma electrolyte concentrations. 4. Dietary supplements of NaHCO3 gave significantly better food conversion and numerically better growth in broilers at 31 degrees C than supplements of potassium bicarbonate (KHCO3) providing similar dietary concentrations of bicarbonate. 5. Supplements of NaHCO3 were more toxic to broiler chickens when supplied in the drinking water than in the diet. This appeared to be related to the intake of sodium and alterations to cellular membrane ionic potential.

Sweating and skin temperature responses of normal and anhidrotic horses to intravenous adrenaline

Anhidrosis has been recognised for over half a century, but despite some excellent epidemiological studies, there has been little progress in understanding the aetiology of the condition. Using a modified ventilated capsule, we obtained dynamic, quantitative data on sweating responses in anhidrotic horses and normal sweating controls from the same environment. Ten horses with current seasonal anhidrosis and 10 matched normal sweating controls were selected. Each horse was given two 10 min infusions of 1 and 2 micrograms/kg/min adrenaline, separated by at least 6 h. Sweating responses and skin temperatures on the neck and gluteal region were measured. Plasma and sweat for analysis of total protein and electrolytes and plasma for analysis of adrenaline were collected. Anhidrotic horses produced significantly less sweat, had lower initial and peak sweat rates and a greater neck:gluteal ratio for sweat production. Plasma adrenaline at rest or at the time of peak sweating rate was not different between groups. In nearly three-quarters of the anhidrotic horses, the shape of the sweat rate against time curve was different compared to controls. Volume of sweat produced was significantly correlated with skin temperature on the neck of controls and anhidrotic horses and on the gluteal region of controls, but not anhidrotic horses. Plasma total protein and electrolyte concentrations were not different between groups. There were significant differences in sweat electrolyte concentrations between controls and anhidrotic horses. These differences were reduced when sweat electrolytes were expressed per g of total protein, and no differences existed when expressed as g/m2. This study has provided insight into the response of anhidrotic horses to beta 2 adrenergic stimulation and may be a useful technique to investigate this condition.

Electrolyte and glycerol supplementation improve water intake by horses performing a simulated 60 km endurance ride.

To replace electrolytes lost in sweat during endurance competitions, riders frequently supplement horses with hypertonic oral electrolyte pastes. To determine whether this practice and concurrent administration of the so-called hyperhydrating substance glycerol are of benefit, weight loss, voluntary water intake, plasma osmolality, and plasma protein and electrolyte concentrations were measured in 6 Arabian horses supplemented with a total of 2.4 ml/kg bwt of water (W); 0.2 g/kg bwt KCl and 0.4 g/kg bwt NaCl in 2.4 ml/kg bwt of water (E); or 0.2 g/kg bwt KCl and 0.4 g/kg bwt NaCl in 2.4 ml/kg bwt (3 g/kg bwt) of glycerol (GE) before and during a treadmill exercise test simulating a 60 km endurance ride. Weight loss was greater (P < 0.01) with W (3.2%) than with E and GE (1.0% and 0.9%, respectively) and was associated (r = -0.85, P < 0.0001) with less (P < 0.01) water intake with W (12.2 l) than with E or GE (23.5 l and 25.8 l, respectively). Plasma osmolality increased to a greater extent (P < 0.01) with GE than with E and was unchanged with W. In contrast, plasma protein concentration decreased (P < 0.01) in the later stages of the simulated ride with E and GE, reflecting plasma volume expansion, but remained unchanged with W. Plasma Na+ and Cl- concentrations increased (P < 0.01) with E and GE and were greater (P < 0.01) than values for W during the second half of the 60 km simulated ride. Despite administration are large amounts of potassium with E and GE, plasma K+ concentration was decreased (P < 0.01) at the end of the rest breaks during the simulated ride and after 60 min of recovery with all supplements. Adverse effects of administration of hypertonic oral electrolyte pastes were not observed and decreases in plasma protein concentration within 30 min after drinking with all supplements suggested that intestinal absorption was well maintained during the simulated endurance ride. In conclusion, electrolyte supplementation in the form of hypertonic oral pastes improved water intake during endurance exercise but concurrent glycerol administration provided no additional benefits in comparison to supplementation with electrolytes alone.

TRAINING-INDUCED ALTERATIONS IN RENAL FUNCTION IN HORSES

1621 Exercise training-induced hypervolemia in the horse is associated with renal mechanisms resulting in a decrease in urine output and net water retention (McKeever et al. M.S.S.E. 19:21-27, 1987 ). Unfortunately, the observed increase in plasma sodium content was not associated with increased sodium intake or a decrease in excretion. Renal function was measured at 7 d intervals; however, mechanisms associated with the retention of sodium and other electrolytes are most active in the first 1-3 days of training. Therefore, the purpose of the present study was to test the hypothesis that repeated exercise would alter renal excretion of electrolytes in horses within the first 3 d of training. Five, healthy, unfit, Standardbred mares (450-500 kg, 4-8 yrs) were used for this study. The experiment consisted of a 2 wk equilibration period followed by a 1 wk control period and a 3 d exercise training period (30 min/d at 60% VO2max). During control, renal fluid and electrolyte losses were measured for 24 hrs on 3 days. Renal function (urine volume, 24 hr Na+, K+, and Cl− excretion, clearance of Na+, K+, and Cl−, creatinine, osmotic substances, and free water, and the fractional excretion of Na+, K+, and Cl−) was measured for an additional 3 d during the training period. There were no differences (p > 0.05) in any variable during the control period. During training, there were no significant changes in plasma osmolality or electrolyte concentrations or creatinine clearance. Training resulted in decreases (p < 0.05) in urine volume (−30%), Na+ excretion (−73%), K+ excretion (−55%), and Cl− excretion (−70%). Training also caused decreases (p < 0.05) in osmotic clearance (−30%), through decreases in the clearance of Na+ (−60%), K+ (−60%), and Cl− (−66%). Interestingly, free water clearance increased (+30%, p < 0.05). Significant decreases in the fractional excretion of Na+ (−59%), K+ (−48%), and Cl− (−60%) suggest that mechanisms affecting tubular conservation of electrolytes rather than reabsorption of solute free water predominate in the effects of repeated exercise on renal function.

Osmoregulation in North American eels ( Anguilla rostrata LeSueur) on land and in freshwater: effects of the corpuscles of Stannius

Hypercalcemia, hypomagnesia and hypophosphatemia were observed in freshwater (FW) eels (Anguilla rostrata LeSueur) after removal of the corpuscles of Stannius. These changes did not occur if Stanniectomized (CSX) eels were removed from FW and placed on land for 12 days but did occur after the eels were returned to FW. Therefore, changes in plasma electrolyte concentrations after CSX depended upon the branchial and/or integumental influx of ions. Plasma Na+, Cl− and osmolal concentrations decreased gradually in both sham-operated (SHM) and CSX eels on land (12 days) and in FW (12 days). Plasma K+almost doubled in both SHM and CSX eels after 4 days on land, remained elevated, and fell abruptly to normal within a day after the eels were returned in FW. After 2 days on land, urine flow rates in SHM and CSX eels had decreased by approximately 85%, osmolar clearance by 50% and positive free-water clearance by more than 90%. Body weights did not decrease when eels were on land so it was concluded that the reduced but continuous renal loss of water was counterbalanced by the integumental uptake of condensed water.

Renal prostanoids: physiological relevance in healthy salt-depleted women.

The effective role played by prostanoids in the control of renal function has been investigated in healthy women with salt depletion. Salt depletion (SD2 group, n = 6) was induced by low sodium chloride dietary intake (< or = 60 mmol per day) and combined treatment with natriuretic and potassium-sparing drugs. At the end of the depletive treatment, the cumulative sodium deficit was 513 +/- 56 mmol. The renal function and urinary excretions of prostaglandin (PG) E2, 6-keto-PGF1 alpha (6KPGF) and thromboxane (Tx) B2 were evaluated during hypotonic polyuria. The basal values of plasma sodium and potassium concentrations, plasma renin activity (PRA) and urinary aldosterone excretion were determined before the induction of hypotonic polyuria. Paired studies were performed in the absence (control) and presence of indomethacin both in the SD2 group and in a previously studied group (N2, n = 6) of healthy women in normal sodium and potassium balance. Women in normal balance received 100 mg i.m. of indomethacin, salt-depleted women received only 50 mg (because 100 mg of the drug produced a prolonged anuria). In the SD2 vs. N2 group in the absence of treatment the following significant differences were found: (a) higher basal values of PRA and urinary aldosterone excretion; (b) higher urinary excretions of 6KPGF and TxB2 but not of PGE2; (c) lower values of urinary flow rate, creatinine clearance, absolute and fractional excretions of sodium and chloride, plasma osmolality and plasma electrolyte concentrations. The effects of the indomethacin have been assessed as percentage variations by using paired data for each experimental group. In the SD2 vs. N2 group the reduction in urinary excretions of 6KPGF, TxB2 and potassium as well as in creatinine clearance were not significantly different. On the other hand, the following were significantly different: (a) the lower reduction in PGE2 excretion; (b) the higher reduction in urinary flow rate and in CH2O; (c) the reductions in absolute and fractional excretions of sodium and chloride, and the increase in plasma potassium concentration, significant in the SD2 group but not in the N2 group. The data suggest that: (1) when stimulated by salt depletion the renal biosynthetic pathways of PGI2 and TxA2 showed greater sensitivity to indomethacin inhibition; (2) the effects of the neurohormonal systems activated by salt depletion were either modulated or mediated by renal prostanoids.

Effect of prolonged restriction of motor activity on primates hydration homeostasis.

It has been assumed that restriction of motor activity (hypokinesia) induces significant changes in body hydration homeostasis. Thus, the objective of this study was to measure body hydration level during prolonged hypokinesia (HK). The studies were done on 12 male Macaca Mulatta (rhesus monkeys) aged three to five years (4.75 to 6.96 kg) during a 15-day period of pre HK and a 90-day period of HK. All primates were divided equally into two groups: monkeys placed under vivarium conditions served as vivarium control primates (VCP) and monkeys subjected to HK served as hypokinetic primates (HKP). For simulation of the HK effect, the HKM group was kept for 90 days in small individual cages that restricted their movements in all directions without hindering food and water intakes. During the pre HK period of 15 days and the HK period of 90 days the following parameters were measured: total body water (TBW), extracellular fluid volume (EFV), intracellular fluid volume (IFV), circulating plasma volume (CPV) and interstitial fluid volume (IsFV), urinary and plasma sodium and potassium, fluid consumption and elimination in urine, and body weight. Significant (p < or = 0.01) decrease in the TBW, IFV, and CPV was observed in the HKP group when compared with the VCP group. In the HKP group EFV and IsFV decreased significantly (p < or = 0.01) when compared with the VCP group only in the initial seven days of the HK period, while after the 7th day progressive increase could be observed. Fluid loss, urinary electrolyte excretion and plasma electrolyte concentration increased significantly (p < or = 0.01), while fluid intakes decreased significantly (p < or = 0.01) in the HKP group when compared with the VCP group. In the HKP group body weight decreased significantly (p < or = 0.01) when compared with the VCP group. In the VCP group the measured parameters did not change significantly when compared with the baseline control values. It was concluded that prolonged exposure to HK induces significant changes in body hydration homeostasis while body dehydration in monkeys caused primarily due to decreased CPV.