Extracellular Fluid Volume Expansion Research Articles

Sodium retention in cirrhotic rats is associated with increased renal abundance of sodium transporter proteins

Liver cirrhosis with ascites is associated with a decrease in renal sodium excretion and therefore sodium retention. In this paper, we utilize transporter-specific antibodies to address the hypothesis that dysregulation of one or more sodium transporters or channels is associated with sodium chloride (NaCl) retention in a rat model of cirrhosis induced by repeated exposure to carbon tetrachloride. Age-matched controls and cirrhotic rats were pair fed to ensure identical NaCl and water intake for 4 days prior to euthanasia for quantitative immunoblotting studies. The rats manifested marked extracellular fluid volume expansion with massive ascites. Plasma aldosterone levels were markedly elevated. Analysis of immunoblots revealed marked increases in the abundances of both of the major aldosterone-sensitive apical transport proteins of the renal tubule, namely the thiazide-sensitive NaCl cotransporter NCC and the epithelial sodium channel alpha subunit (alpha-ENaC). These results are consistent with an important role for hyperaldosteronism in the pathogenesis of sodium retention and ascites formation in cirrhosis. In addition, we observed a large decrease in cortical NHE3 abundance (proximal tubule) and a large increase in NKCC2 abundance (thick ascending limb), potentially shifting premacula densa sodium absorption from proximal tubule to loop of Henle (which powers urinary concentration and dilution).

Uses and Effectiveness of Pamidronate Disodium for Treatment of Dogs and Cats with Hypercalcemia

Uncorrected hypercalcemia can cause clinical signs such as polyuria, polydipsia, vomiting, diarrhea, lethargy, and depression and contributes to the development of primary renal failure and soft tissue mineralization. Treatment of hypercalcemia includes diagnosis and treatment of the underlying disease process and some combination of excracellular fluid volume expansion by administration of fluids intravenously and administration of glococorticosteroids, salmon calcitonin, and furosemide. Bisphosphonates such as pamidronate disodium also may be safe and effective in the treatment of hypercalcemia. The purpose of our study was to characterize the efficacy and safety of pamidronate in the treatment of hypercalcemia attritutable to several different disease processes in the dog and cat. Seven dogs and 2 cats were administered pamidronate at a dose of 1.05-2.0 mg/kg IV for a variety of disease processes, including neoplasia (n = 4), calcipotriene toxicity (n = 3), nocardiosis (n = 1), and idiopathic hypercalcemia with chronic renal failure (n = 1). In all the animals, IV pamidronate administration rapidly decreased serum calcium concentrations without evident toxicosis. Two animals received pamidronate several times without obvious toxicosis. On the basis of the findings in our retrospective study, pamidronate may be a safe and effective drug with which to lower both serum total and ionized calcium concentrations in patients with hypercalcemia arising from a wide variety of underlying disease processes.

The role of chloride in deoxycorticosterone hypertension: selective sodium loading by diet or drinking fluid.

To evaluate the role of chloride in the pathogenesis of salt-dependent deoxycorticosterone (DOC) hypertension, we studied young Wistar rats chronically loaded with sodium bicarbonate (NaHCO(3)) or sodium chloride (NaCl) which were administered either in the diet or in the drinking fluid. Selective sodium loading (without chloride) increased blood pressure (BP) in DOC-treated animals only if NaHCO(3) was provided in the diet. In contrast, no significant blood pressure changes were induced by DOC treatment in rats drinking NaHCO(3) solution. Hypernatremia and high plasma osmolality occurred only in rats drinking NaCl or NaHCO(3) solutions. Compared to great volume expansion in NaCl-loaded DOC-treated rats, the degree of extracellular fluid volume expansion (namely of its interstitial fraction) was substantially lower in both NaHCO(3)-loaded groups in which significant hypokalemia was observed. NaHCO(3)-drinking rats without significant blood pressure response to DOC treatment represented the only experimental group in which blood volume was not expanded. In conclusion, our data confirm previous observations that NaHCO(3) loading is less potent in eliciting DOC hypertension than NaCl loading, but blood pressure rise in rats fed NaHCO(3) diet clearly demonstrated that selective sodium loading could potentiate the development of DOC hypertension if NaHCO(3) is offered within the appropriate dietary regimen. The reasons for the failure of NaHCO(3)-drinking rats to elevate blood pressure in response to chronic mineralocorticoid treatment are not obvious. However, the absence of a significant plasma volume expansion together with hypernatremia and increased plasma osmolality suggest a considerable degree of dehydration in these animals which fail to increase their fluid consumption compared to water drinking rats.

Natriuresis and the extracellular volume expansion by hypertonic saline

Background The mechanisms governing the duration of the extracellular fluid volume (ECF) expansion as a result of intravenous infusion of hypertonic saline solution are poorly understood. We hypothesized that the duration is closely related to the sodium excretion. Materials and methods Six conscious splenectomized ewes with a mean body weight of 30 kg were given an intravenous infusion of 4 ml kg –1 of 7.5% saline solution on two occasions, one over a period of 5 min and another over a period of 20 min. Mass balance and volume kinetic calculations of the distribution and elimination of fluid were performed after repeated sampling of the plasma sodium concentration and the urinary excretion of water and sodium during 3 h. Results On considering the addition of sodium to and its excretion from the body, the plasma sodium concentration indicated a 10% dilution of the extracellular space. The volume expansion decayed at an average rate of 20% of the volume expansion per hour, which, however, varied greatly in the animals, depending on their capacity to excrete sodium. After 1 h, increasing natriuresis promoted translocation of water into the cells, which amounted to 25–35% of the total elimination. Computer simulations indicated that tripled natriuresis (up to approximately 750 mmol l –1) would increase the rate of elimination to 45% of the volume expansion per hour. Conclusion The sodium excretion was inversely proportional to the duration of the extracellular volume expansion by 7.5% saline.

MECHANISMS FOR ESTROGEN AND PROGESTERONE EFFECTS ON PLASMA VOLUME

Adequate plasma volume (PV) and extracellular fluid volume (ECFV) are essential for exercise performance. PURPOSE To test the hypothesis that estrogen acts on vessels to reduce vascular permeability to proteins, thereby reducing protein and fluid movement out of the vasculature and increasing PV. METHODS We suppressed estrogen (E) and progesterone (P) with a gonadotropin releasing hormone antagonist (GnRHa) in four women (N=4, 23±1 y). Subjects used GnRHa for 16 days, E for days 4–16, and P for days 13–16. We estimated extracellular fluid volume (inulin washout), transcapillary escape rate of albumin (TERalb) and PV with Evans Blue dye on days 2 (GnRHa), 9 (E) and 16 (E/P). RESULTS Plasma [E] increased from 15±2 to 74±21 to 216±84 pg/ml and plasma [P] from 0.9±0.3 to 1.0±0.4 to 16±8.3 ng/ml for GnRHa, E and E/P, respectively. Both E (44.2±5.1 ml/kg) and E/P (45.4 ± 3.9 ml/kg) increased PV compared to GnRHa (42.6±2.2 ml/kg). Within subjects TERalb was a strong predictor of PV (r=0.81), and TERalb was lowest during E (5.4±0.8, 3.0±0.5 and 3.7 %/hr for GnRHa, E and E/P, respectively). ECFV was greater during E/P (270 ml/kg) compared to both GnRHa (223±17) and E (180±26 ml/kg). Thus the percentage of extracellular fluid in the plasma compartment increased from 19.4 % (GnRHa) to 24.8 % during E and decreased to 16.8 % during E/P. CONCLUSION E administered alone enhanced PV via actions on capillaries that lowered the rate of protein, and thus water movement out of the circulation. Thus with E, water was selectively retained in the plasma. When P was administered with E, PV increased via ECFV expansion. The different mechanisms for PV increase may be explained the greater P[P] or P[E] or the change in E:P ratio. NIH HL62240-02.

The Prognostic Role of Atrial Natriuretic Peptides in Hemodialysis Patients

Background: It is well known that plasma atrial natriuretic peptide (ANP) is an indicator of extracellular fluid volume expansion and that plasma ANP is considered to be a marker for setting the proper dry weight of HD patients. Although the plasma ANP is a prognostic predictor of cardiac death, the prognostic role of ANP in HD patients has yet to be elucidated. In this study, we investigated the prognostic role of ANP in HD patients. Methods: Plasma ANP concentrations were measured in 105 HD patients after HD. Multiple regression analysis was performed to determine the major factors causing increased plasma ANP concentrations. Cardiac mortality was monitored for 24 months after baseline analysis, and the prognostic role of ANP was examined by Cox proportional hazards regression analysis. Results: Multiple regression analysis showed that cardiovascular disease (CD) and age were independent factors for elevated ANP (R² = 0.298, p < 0.0001). During a 24-month follow-up period, cardiac death occurred in 11 patients. Kaplan- Meier survival estimates of patients from varying plasma ANP levels (<50 and >50 pg/ml) differed between the two groups (p < 0.0001). The group with the higher ANP level (>50 pg/ml) had the lower survival. When compared with patients with ANP <50, the hazard ratios for cardiac death of patients with ANP of >50 pg/ml were 32.0 (95% confidence interval (CI) 4.1 to 252.4). Univariate Cox proportional hazards model showed that ANP, left ventricular ejection fraction (LVEF), LVMI, age, serum albumin and C-reactive protein (CRP) were significantly associated with the risk of cardiac mortality. By stepwise multivariate Cox proportional hazards analysis, only ANP, LVMI and CRP remained powerful independent predictors of cardiac death. The relative risk ratios were 3.483 (95% CI 1.640–7.397) for ln ANP, 1.023 (1.008–1.038) for LVMI, and 1.379 (1.115–1.705) for CRP. Conclusion: High plasma ANP level of post-HD were strongly associated with CD and age. Post-HD ANP level may be a reliable parameter for assessing the risk for cardiac death in HD patients by providing prognostic information independent of other variables previously reported.

Renoprotective effects of chronic candesartan treatment in uninephrectomized rat.

The authors recently observed an age-dependent reduction in the diuretic and natriuretic responses to plasma volume expansion in uninephrectomized control and glucose-intolerant rats. To determine the involvement of angiotensin II AT receptors in this phenomenon, the authors tested the hypothesis that chronic candesartan treatment preserves renal excretory function in the uninephrectomized rat. Control and glucose-intolerant rats underwent right nephrectomy at 4 weeks of age. Two weeks later, the animals in each group were further subdivided and maintained on tap water containing either candesartan cilexetil (10 mg. kg(-1). day(-1) ) or vehicle. Renal excretory responses to acute extracellular fluid volume expansion (5% of body weight over 30 min) were determined in the 9-month-old conscious animal. Candesartan treatment markedly reduced the mean arterial pressure of controls and glucose-intolerant rats. Nonetheless, the baseline rates of fluid and electrolyte excretion, as well as the saline volume-induced diuretic, natriuretic, and kaliuretic responses, were greater in the candesartan-treated rats than in their vehicle-treated counterparts. The augmented baseline rates of fluid and sodium excretion in candesartan-treated rats were caused by a reduction in tubular reabsorption activity and an increase in glomerular filtration rate. However, the candesartan-mediated enhancement in saline volume-induced diuresis and natriuresis was caused by a reduction in tubular reabsorption activity. In addition to improving renal function, candesartan treatment reduced proteinuria in both groups. In conclusion, chronic blockade of the angiotensin II receptors exerts hypotensive and renoprotective effects in the aging uninephrectomized rat.

Cerebral salt wasting: Truths, fallacies, theories, and challenges

The reported prevalence of cerebral salt wasting has increased in the past three decades. A cerebral lesion and a large natriuresis without a known stimulus to excrete so much sodium (Na ) constitute its essential two elements. To review the topic of cerebral salt wasting. There is a diagnostic problem because it is difficult to confirm that a stimulus for the renal excretion of Na is absent. Review article. None. Three fallacies concerning cerebral salt wasting are stressed: first, cerebral salt wasting is a common disorder; second, hyponatremia should be one of its diagnostic features; and third, most patients have a negative balance for Na when the diagnosis of cerebral salt wasting is made. Three causes for the large natriuresis were considered: first, a severe degree of extracellular fluid volume expansion could down-regulate transporters involved in renal Na resorption; second, an adrenergic surge could cause a pressure natriuresis; and third, natriuretic agents might become more potent when the effective extracellular fluid volume is high. Cerebral salt wasting is probably much less common than the literature suggests. With optimal treatment in the intensive care unit, hyponatremia should not develop.

Effect of hydrostatic pulmonary edema on the interparabronchial septum of the chicken lung

Scanning electron microscopy (SEM) was utilized to examine the interparabronchial septum as a potential site of lymphatic drainage in the lungs of anesthetized chickens (Gallus domesticus). Birds were subjected to extracellular fluid volume expansion in order to produce hydrostatic pulmonary edema via increased pulmonary capillary fluid flux into the interstitial spaces of the lung. Micrographs obtained from freeze-dried lungs of volume-loaded birds were compared with similarly prepared lungs from normal control chickens, which were not volume loaded. The adjacent parabronchi of the control lungs were closely opposed by a minimal septal space, whereas the interparabronchial septal space of the volume-loaded birds was measurably thickened and appeared to be engorged as a result of hydrostatic pulmonary edema. The results of this study are consistent with observations of the lungs of mammals subjected to hydrostatic pulmonary edema and suggest that the interparabronchial septum may be a potential route of lymphatic drainage in the avian lung.

Low-dose desmopressin infusion: renal action in healthy women in moderate salt retention and depletion, and interactions with prostanoids

Studies were carried out to evaluate the influence of variations in sodium balance on the renal response to low-dose infusion of 1-desamino-8- D -arginine vasopressin (dDAVP), and the functional interaction between dDAVP and renal prostanoids. The studies were performed on healthy women in conditions of extracellular fluid volume expansion (SR group, n =9) and depletion (SD2 group, n=6), respectively. The study protocol included hypotonic polyuria (induced by oral water load) and subsequent antidiuresis (induced by low-dose infusion of dDAVP). Three 60-min clearance (cl.) periods were performed during polyuria (cl. P), early (cl. A1) and late (cl. A2) antidiuresis. The urinary concentrations of prostaglandin (PG) E 2 and the stable metabolites of PGI 2 and thromboxane (Tx) A 2, 6-keto-PGF 1α (6KPGF) and TxB 2, were estimated. Paired renal functional explorations were performed in salt retention and salt depletion both in absence and presence of indomethacin (SR.I and SD2.I groups). In both paired and unpaired studies, the early and late effects of dDAVP on the functional excretory variables and the excretion of prostanoids were assessed as percentage variations, (A1−P)% P and (A2−A1)% A1. (I) dDAVP in salt retention and depletion. During early infusion dDAVP produced in both conditions a significant reduction in urinary flow rate, creatinine cl., absolute and fractional excretions of sodium, chloride and potassium; during late infusion dDAVP was effective in inducing a further significant reduction in urinary flow rate. In salt retention compared to depletion the early reductions in sodium and chloride (absolute and fractional) excretions were significantly lower. (II) Indomethacin pretreatment. During early infusion the dDAVP-induced reductions in the urinary flow rate and 6KPGF excretion were enhanced in both conditions. In salt depletion the dDAVP effects in reduction of creatinine cl. and urinary electrolyte excretions were also enhanced. During late infusion the antidiuretic effect of dDAVP was suppressed in salt retention, while in salt depletion creatinine cl., the urinary excretions of electrolytes and both 6KPGF and TxB 2 showed increases significantly different from the dDAVP effects in the absence of indomethacin. In conclusion, (a) the salt-retaining effect of dDAVP was less effective in salt retention compared to depletion. (b) Indomethacin pretreatment affected the renal action of dDAVP in a time-dependent pattern. The early effects in both conditions were consistent with an inhibited synthesis of modulator PGs. On the contrary, the late effects were consistent with the occurrence, at least in salt depletion, of an escape from dDAVP renal action. This escape phenomenon probably depended on a partial regression of the pharmacological inhibition of the modulating PGs.

Effect of Extracellular Fluid Volume Expansion on the Interparabronchial Septum of the Avian Lung

Scanning electron microscopy was used to examine the interparabronchial septa of chickens as a potential site of lymphatic drainage in the avian lung. Anaesthetized chickens were subjected to extracellular fluid volume expansion to produce pulmonary oedema as a result of increased capillary fluid flux into the interstitial spaces of the lung. In normal (control) chickens, the adjacent parabronchi were separated by a minimal septal space. In the “volume-loaded” birds, however, the interparabronchial septal spaces were measurably thickened and engorged as a result of hydrostatic pulmonary oedema. These results, which were consistent with reports of the effect of hydrostatic pulmonary oedema in mammals, suggest that the interparabronchial septum is a potential route of lymphatic drainage in the avian lung.

Effects of dopamine and nitric oxide on arterial pressure and renal function in volume expansion.

1. The aim of the present study was to investigate the role of dopamine (DA) in the hypotensive and renal effects of L-arginine during extracellular fluid volume expansion (10% bodyweight). 2. Animals were randomized to non-expanded and expanded groups. Both groups received different treatments: L-arginine (250 mg/kg, i.v.), N(G)-nitro-L-arginine methyl ester (L-NAME; 1 mg/kg, i.v.), haloperidol (3 mg/kg, i.p.) and L-arginine + haloperidol (n = 8). Mean arterial pressure (MAP), diuresis, natriuresis, kaliuresis, glomerular filtration rate, renal plasma flow (RPF) and nitrite and nitrate (NO(x)) excretion were determined. 3. The increase in MAP induced by L-NAME was greater in expanded than in non-expanded rats (42 +/- 3 vs 32 +/- 3 mmHg, respectively; P < 0.01). Administration of haloperidol did not modify the L-arginine hypotensive effect. 4. Blockade of nitric oxide synthase diminished urine flow in non-expanded (4.15 +/- 0.56 vs 0.55 +/- 0.11 microL/min per 100 g; P < 0.01) and expanded animals (24.42 +/- 3.67 vs 17.85 +/- 2.16 microL/min per 100 g; P < 0.01). Diuresis induced by L-arginine was reduced by DA blockade in both non-expanded (17.15 +/- 2.11 vs 6.82 +/- 0.61 microL/min per 100 g; P < 0.01) and expanded animals (44.26 +/- 8.45 vs 25.43 +/- 5.12 microL/min per 100 g; P < 0.01). 5. Sodium excretion decreased with L-NAME treatment in non-expanded (0.22 +/- 0.03 vs 0.06 +/- 0.01 microEq/min per 100 g; P < 0.01) and expanded animals (3.72 +/- 0.70 vs 1.89 +/- 0.23 microEq/min per 100 g; P < 0.01). Natriuresis induced by L-arginine was diminished by haloperidol both in non-expanded (0.94 +/- 0.13 vs 0.43 +/- 0.04 microEq/min per 100 g; P < 0.01) and expanded rats (12.77 +/- 0.05 vs 3.53 +/- 0.75 microEq/min per 100 g; P < 0.01). Changes in kaliuresis changes seen following treatment with L-arginine, L-NAME and L-arginine + haloperidol followed a pattern similar to that observed for sodium excretion in both groups of rats. 6. L-arginine enhanced RPF in non-expanded animals (11.96 +/- 0.81 vs 14.52 +/- 1.05 mL/min per 100 g; P < 0.01). Glomerular filtration rate was increased by extracellular volume expansion (3.08 +/- 0.28 vs 5.42 +/- 0.46 mL/min per 100 g; P < 0.01). 7. The increase in NOx induced by acute volume expansion (0.18 +/- 0.03 vs 0.52 +/- 0.08 nmol/min per 100 g; P < 0.01) was diminished following the administration of haloperidol (0.52 +/- 0.08 vs 0.26 +/- 0.06 nmol/min per 100 g; P < 0.01). 8. Although DA does not participate in the actions of nitric oxide on vascular tone, both systems would play an important role in renal function adaptation during extracellular fluid volume expansion.

Extracellular fluid volume expansion in patients with posturally related syncope.

This review will focus on the management ofpatientswith orthostatic disorders by chronic expansion oftheextracellular fluid volume.Studies in two main groups ofpatients will be discussed.First,we will consider effectsin patients with chronic primary autonomic failure,whohave structural disorders with permanent failure ofcir-culatory control and severe symptomatic orthostatic hy-potension.The majority ofreports ofthis rare disorderrefer to fewer than 10 patients studied.However,by care-ful evaluation ofthis small number ofpatients,valuableinformation has been obtained about the pathophysiol-ogy oforthostatic dysregulation and its treatment [1,2].Management strategies developed in patients withprimary autonomic failure have been important for thesecond group of patients that we will discuss,i.e.,pa-tients with functional disorders with occasional failureoforthostatic blood pressure control and episodic pos-turally related syncope.In contrast to chronic primaryautonomic failure this condition is very common [3].Itincludes disorders like vasovagal fainting, situationalsyncope,and postural tachycardia.The first section ofthis review is concerned with the shifts in extracellularvolume induced by orthostatic stress,the second sectionwith sodium intake and orthostatic tolerance,and theremaining sections with the effects ofexercise trainingand the effects ofhead-up tilt sleeping.

Decreased abundance of collecting duct urea transporters UT-A1 and UT-A3 with ECF volume expansion

Clinical disorders of extracellular fluid (ECF) volume regulation are often associated with changes in plasma urea concentration. To investigate possible renal causes, we measured the relative abundance of the urea transporters UT-A1, UT-A2, and UT-A3 in renal medulla of rats with aldosterone-induced NaCl retention. ECF volume-expanded rats received aldosterone by osmotic minipump plus a diet containing a high level of NaCl. Control rats received the same infusion of aldosterone plus a virtually NaCl-free diet, which prevented ECF volume expansion. Preliminary measurements demonstrated transient positive Na and water balance, decreased serum urea concentration, and increased urea clearance, but no change in creatinine clearance. Immunoblotting of homogenates from inner medulla showed a marked decrease in the abundance of the collecting duct urea transporters UT-A1 and UT-A3. There were no differences in the abundance of UT-A2, aquaporin (AQP)-2, AQP-3, or AQP-4 in ECF volume-expanded rats vs. controls. Time course experiments demonstrated that changes in UT-A1 abundance paralleled the fall in serum urea concentration after the switch from a low-NaCl to a high-NaCl diet, whereas the fall in UT-A3 abundance was delayed. Candesartan administration markedly decreased the abundance of UT-A1 and UT-A3 in the renal inner medulla, which is consistent with a role for the angiotensin II type 1 receptor in urea transport regulation. The results support the view that ECF-related changes in serum urea concentration are mediated, at least in part, through altered urea transporter abundance.

Hypertension in hemodialysis patients.

Hypertension is very common and often poorly controlled in patients undergoing chronic hemodialysis. While high blood pressure has been documented to adversely impact several intermediate outcomes of cardiovascular disease, whether hypertension is an independent risk factor for mortality in this population is not clear. Expansion of extracellular fluid volume is the major pathophysiologic mechanism for the development of hypertension in these patients; however, alterations in other humoral mechanisms also play a significant role. Optimization of volume status is, therefore, the cornerstone of therapy with additional use of antihypertensive medications as needed. Good quality prospective studies are urgently needed to define the measurement techniques and blood pressure goals, and to develop therapeutic strategies for more effective management of hypertension in this high-risk population.

Effect of acute saline volume expansion in the anaesthetised DeltaF508 cystic fibrosis mouse.

It has been suggested that CFTR Cl(-) channels in the renal inner medullary collecting duct may be involved in mediating increased renal salt excretion during extracellular fluid volume expansion. To investigate this hypothesis, in-vivo clearance experiments were performed comparing wild-type (WT) and DeltaF508-CFTR transgenic mice (cftr (tm2Cam)). Control animals were given a 0.1-ml bolus of 0.9% saline, followed by I.V. infusion at 0.3 ml x h(-1). Volume expansion was applied by infusing a 1-ml bolus of 0.9% saline followed by infusion at 0.6 ml x h(-1). No significant differences in renal NaCl handling between WT mice ( C(Na)=1.2 +/- 0.3 microl x min(-1), C(Cl)=4.0 +/- 0.5 microl x min(-1)) and DeltaF508-CFTR mice ( C(Na)=1.7 +/- 0.5 microl x min(-1), C(Cl)=4.1 +/- 0.8 microl x min(-1)) were observed under control conditions. Volume expansion resulted in large significant increases in NaCl clearance in both WT mice ( C(Na)=7.0 +/- 0.9 microl x min(-1), C(Cl)=12.0 +/- 0.6 microl x min(-1)) and DeltaF508-CFTR mice ( C(Na)=7.2 +/- 1.6 microl x min(-1), C(Cl)=11.0 +/- 2.2 microl x min(-1)). However, there was no significant difference between WT and DeltaF508-CFTR mice. In conclusion, renal NaCl excretion is not significantly different under basal conditions and during saline volume expansion in DeltaF508-CFTR mice. The data suggest that CFTR is not a physiologically important mediator of volume natriuresis.

Effects of L-arginine and furosemide on blood pressure and renal function in volume-expanded rats.

1. The aim of the present study was to investigate the effects of L-arginine (L-Arg) on blood pressure and water and electrolyte excretion in control and extracellular fluid volume-expanded rats (10% bodyweight with 0.9% NaCl) and to determine whether diuretic treatment with furosemide (FUR) can be optimized by the administration of L-Arg in this model. 2. Both groups of animals were anaesthetized, divided into groups and treated with either 7.5 mg/kg FUR, 250 mg/kg L-Arg, 1 mg/kg NG-nitro-L-arginine methyl ester (L-NAME), FUR + L-NAME or FUR + L-Arg. Mean arterial pressure (MAP), diuresis, natriuresis and kaliuresis were determined. 3. Extracellular fluid volume expansion induced no changes in MAP in control and volume-expanded rats (92+/-6 vs 100+/-8 mmHg, respectively). The hypotension induced by FUR in control and volume-expanded rats (69+/-7 and 76+/-5 mmHg, respectively) was significantly (P < 0.01) enhanced by the administration of L-Arg (54+/-3 and 64+/-3 mmHg, respectively). 4. Injection of L-NAME increased MAP and diminished diuresis, natriuresis and kaliuresis in both groups. 5. Furosemide-induced water and electrolyte excretion was blunted by the administration of L-NAME. 6. The combination of L-Arg + FUR increased diuresis induced by FUR alone (control rats: 29.33+/-1.68 vs 12.91+/- 0.41 microL/min per 100 g, respectively; volume-expanded rats: 248.5+/-25.4 vs 112,6+/-8.3 microL/min per 100 g, respectively; P < 0.01). 7. The administration of the combination of L-Arg + FUR promoted a decrease in the sodium/water excretion ratio compared with the administration of FUR alone (control rats: 0.230+/-0.018 vs 0.45+/-0.03, respectively, P < 0.001; volume-expanded rats: 0.091+/-0.010 vs 0.22+/-0.03, respectively, P < 0.01). 8. The potassium/water excretion rate induced by FUR alone and in the presence of L-Arg followed a pattern similar to that seen for natriuresis (control rats: 0.35+/-0.05 vs 0.20+/-0.05 microEq/min per 100 g, respectively; volume-expanded rats: 0.045+/-0.008 vs 0.014+/-0.003 microEq/min per 100 g, respectively; P < 0.01). 9. The decrease in the electrolyte/water excretion ratio observed with FUR + L-Arg in volume-expanded rats was greater than in control animals. 10. The results of the present study show that the administration of FUR with L-Arg contributes to enhanced hypotensive and diuretic effects of FUR, thus diminishing the relative electrolyte excretion in normal conditions and in extracellular fluid volume expansion.

The selective adenosine A 1 receptor antagonist KW-3902 prevents radiocontrast media-induced nephropathy in rats with chronic nitric oxide deficiency

Several studies have recently suggested a principal role of adenosine in the pathogenesis of radiocontrast media-induced nephropathy. In the present experiments, we therefore investigated the renal protective effects of 8-(noradamantan-3-yl)-1,3-dipropylxanthine (KW-3902), a potent and selective adenosine A 1 receptor antagonist, on radiocontrast media-induced nephropathy in the model of the N-ϖ-nitro- l-arginine methyl ester ( l-NAME) hypertensive, chronic nitric oxide (NO)-depleted rat. Chronic NO depletion was induced by pretreatment with l-NAME, 50 mg/ml, added to drinking water for 8 weeks. Clearance experiments were performed in anesthetized rats and glomerular filtration rate was assessed prior to and following the application of high osmolar radiocontrast media (sodium diatrizoate, 3 ml/kg, i.v.) or an equivalent volume of isoosmolar mannitol to examine the role of hyperosmolarity in radiocontrast media-induced nephropathy. Subgroups received KW-3902 (0.1 mg/kg, i.v.), 20 min prior to radiocontrast media administration. Age-matched, untreated rats served as controls. Radiocontrast media application induced a significant decline in glomerular filtration rate in l-NAME hypertensive animals, whereas no effects were observed in control rats. KW-3902 fully prevented the drop in glomerular filtration rate in response to radiocontrast media in l-NAME hypertensive rats. No renal hemodynamic alterations were observed in mannitol-infused animals. The present experiments demonstrate that the decrease in glomerular filtration rate following radiocontrast media occurred independently of the osmotic load, and that KW-3902 effectively prevented the radiocontrast media-induced deterioration in renal function. KW-3902 may be especially beneficial in patients at high risk for developing acute renal failure following radiocontrast media application or in patients in which extracellular fluid volume expansion is limited by clinical conditions such as congestive heart failure.

Response of Air Sac Mesothelium to Expansion of Extracellular Fluid Volume in Gallus domesticus

In this study, scanning electron microscopy was used to examine the effects of hydrothorax on the morphology of the air sac visceral mesothelium of Gallus domesticus. Anaesthetized chickens were subjected to acute hydrodynamic pulmonary oedema induced by expansion of the extracellular fluid volume with an infusion of Ringer's solution equal to 6·5% of body weight. Tissue samples from the visceral surface of the abdominal air sacs near their ostia were obtained and fixed after death induced by anaesthetic overdose. These were compared with similar samples from control “non-volume-loaded” birds. The air sac visceral mesothelium of the volume-loaded animals presented an increased density of bulbous or swollen microvilli. These deformations were similar to changes reported in the visceral pleura of mammals subjected to hydrothorax, suggesting a commonality with regard to the role of these mesothelia in liquid clearance during pulmonary oedema.

Renal response to volume expansion: learning the experimental approach in the context of integrative physiology.

We describe a laboratory experience for upper-level science students that provides a hands-on approach to understanding the basics of experimental physiology. A pre-lab, interactive tutorial develops the rationale for this experiment by reviewing the renal and cardiovascular mechanisms involved in the response to extracellular fluid volume expansion. After a hypothesis is stated, an experiment is designed to determine the relative importance of dilution of plasma proteins to the overall renal excretory response following volume expansion with intravenous saline. In the lab, students collect data from two groups of anesthetized rats. The protocol involves continuous monitoring of arterial pressure and periodic collection of urine and blood samples after volume expansion with either isotonic NaCl or isotonic NaCl plus 5% albumin. A post-lab tutorial is used to analyze, interpret, and discuss the data. Students next prepare an oral presentation, practice it, and finally present their results and answer questions before peers and instructors. This overall experience involves all of the components of doing a "real" experiment, starting with a question that is not answered in general textbooks of physiology and finishing with an oral presentation of the results. Along the way, students gain a better understanding of a complex homeostatic response and learn the care and value of using animals in research and teaching.