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PubMed2003

Reduction of oxidative stress augments natriuretic effect of furosemide in moderate heart failure.

BACKGROUND: The significance of antioxidant therapy in heart failure has not been fully examined. This study evaluated whether vitamin C has beneficial effects on renal function or augments the renal effects of furosemide in patients with heart failure. METHODS: There were 2 protocols. In protocol 1, plasma level of thiobarbituric acid-reactive substances (TBARS) and renal function were assessed before and after intravenous infusion of vitamin C or placebo in 8 patients with moderate congestive heart failure (CHF) treated with enalapril. In protocol 2, a randomized crossover study was performed in patients with moderate CHF treated with either an ACE inhibitor (enalapril) (n = 10) or an angiotensin II receptor antagonist (losartan) (n = 9) and in asymptomatic patients with impaired left ventricular function treated with enalapril (n = 8). TBARS and renal function were assessed before and after intravenous infusion of furosemide alone, coinfusion of furosemide with placebo and vitamin C, or coinfusion of furosemide with vitamin C and a kallikrein inhibitor (nafamostat mesilate). RESULTS: In protocol 1, although vitamin C reduced TBARS, it did not affect renal function. In protocol 2, TBARS was higher in patients with moderate CHF than in asymptomatic patients. Vitamin C augmented natriuretic effect of furosemide (from 179 +/- 98 to 192 +/- 104 micromol/min, P <.01) only in patients with moderate CHF treated with enalapril but not in the other 2 groups. Nafamostat mesilate prevented this augmentation. CONCLUSIONS: In patients with CHF treated with enalapril, counteraction of the increased oxidative stress by vitamin C may contribute to the augmented natriuretic effect of furosemide through the renal kinin-nitric oxide pathway.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed2006

Increased urinary aquaporin-2 excretion in response to furosemide in patients with chronic heart failure.

OBJECTIVE: Patients with chronic heart failure (CHF) have decreased ability to excrete water and increased urinary excretion of aquaporin-2 (U-AQP2). The natriuretic and diuretic effects of furosemide are antagonized by an increased reabsorption of sodium and water in the collecting ducts. It is unknown whether aquaporin-2 (AQP2) renal water channels are involved in this compensatory reabsorption. We tested the hypothesis that U-AQP2 increases after a single intravenous dose of furosemide in CHF patients. MATERIAL AND METHODS: In a randomized, single-blind, placebo-controlled, crossover study, we measured the effect of furosemide (80 mg) on U-AQP2, urine volume, free water clearance (C(H2O)) and fractional excretion of sodium (FE(Na)) in 12 CHF patients. Plasma concentrations of vasopressin (AVP), renin (PRC), angiotensin II (Ang II), aldosterone (Aldo), atrial (ANP) and brain natriuretic peptides (BNP) were measured during the study. U-AQP2 and hormones were determined by radioimmunoassays. RESULTS: Furosemide increased U-AQP2 (140 %), urine volume (280 %), C(H2O) (95 %) and FE(Na) by a factor of 15 (p<0.008 for all), and also AVP (51 %), PRC, Ang II (86 %) and Aldo (59 %) (p<0.021 for all). ANP and BNP did not change. CONCLUSIONS: In CHF, furosemide increased the vasopressin level, which stimulated water reabsorption via the APQ2 water channels. This is most likely a compensatory phenomenon in addition to the increase in the renin-angiotensin system to prevent excess loss of sodium and water. However, both these effects were overridden by the effect of furosemide, as shown by increased free water clearance and sodium excretion.

Adult↗
PubMed2005

Urinary excretion of aquaporin-2 after furosemide and felodipine in healthy humans.

OBJECTIVE: Furosemide inhibits renal sodium and chloride reabsorption in the loop of Henle. A compensatory increased reabsorption of sodium and water takes place in the collecting duct. It is not known whether aquaporin-2 (AQP2) renal water channels are involved in this compensatory reabsorption. In animals, dihydropyridine derivatives of calcium channel blockers down-regulate AQP2 in the collecting duct, but the effect has not been studied in humans. We sought to test the hypotheses that urinary excretion of aquaporin-2 (U-AQP2) increases after a single intravenous dose of furosemide, and that U-AQP2 decreases after a single oral dose of felodipine. MATERIAL AND METHODS: In two randomized, single-blind, placebo-controlled, cross-over studies, we measured the effect of furosemide and felodipine on U-AQP2, urine volume, free water clearance (CH2O), and fractional excretion of sodium (FENa) in 13 healthy subjects in each study. Plasma concentrations of vasopressin (AVP), renin (PRC), angiotensin II (ang II), aldosterone (aldo), atrial (ANP), and brain natriuretic peptides (BNP) were measured during the study. Glomerular filtration rate (GFR) was measured by constant infusion technique. U-AQP2 and hormones were determined by radioimmunoassay. RESULTS: Furosemide treatment increased U-AQP2 (202%), urine volume (214%), and FENa by a factor of 11, (p < 0.001 for all), whereas CH2O and GFR were unchanged. After treatment with placebo, no differences were seen. Furosemide treatment increased AVP (18%), PRC (60%), ang II (100%), and aldo (98%) (p < 0.032); ANP was decreased by 29% (p < 0.001), whereas there was no change in BNP. The hormones were unchanged after placebo except for a minor decrease in ANP after placebo. Felodipine tended to increase U-AQP2, to decrease CH2O and urine volume and GFR, and to increase FENa, but the effect was not significantly different from placebo. Felodipine increased PRC (82%) (p < 0.003) and ang II, but decreased aldo, and increased AVP. After placebo, PRC was unchanged, whereas ang II, aldo and AVP were changed as after felodipine. CONCLUSIONS: Furosemide treatment increased U-AQP2, AVP, and the activity of the renin-angiotensin-aldosterone system. These changes are most likely compensatory phenomena, which prevent an excess loss of sodium and water. Felodipine tended to increase U-AQP2.

Adult↗
PubMed2002

Furosemide and spironolactone reduce transmigration of leukocytes through endothelial cell monolayers.

Furosemide and spironolactone reduce transmigration of leukocytes through endothelial cell monolayers. Leukocytes play a tremendous role during inflammation. Leukocytes migrate from intravascular space into the tissue to attack microorganisms. Various agents are able to influence leukocyte recruitment. The influence of diuretics, such as furosemide and spironolactone, on inflammatory processes is not well known. The aim of our study was to examine the influence of furosemide and spironolactone on leukocyte migration through endothelial cell monolayers (ECM). Human umbilical vein endothelial cells were cultured on microporous membranes achieving a monolayer. Polymorphonuclear leukocytes (PMNL) were used in a currently described migration assay. PMNL and/or ECM were pretreated with furosemide and spironolactone using therapeutic, as well as higher and lower, concentrations. Furosemide (76 +/- 7.2%) and spironolactone (70 +/- 7.7%) were able to inhibit PMNL migration through ECM significantly, when both cell types were treated simulating the situation after an iv injection. Furosemide and spironolactone were identified as potent inhibitors of leukocyte migration through ECM.

Cell Adhesion↗
PubMed2000

Structure-solubility relationship and thermal decomposition of furosemide.

Furosemide, a high ceiling diuretic, decomposes on heating and is very sparingly soluble in water. The aim of this study was to identify the thermal decomposition product(s) of furosemide and to calculate the activation energy needed for this reaction. This was done to gain a better understanding of the unusually low water solubility of this drug. The main thermal decomposition product was identified by nuclear magnetic resonance (NMR), mass spectrometry (MS), and infrared (IR) analysis as 4-chloro-5-sulfamoylanthranilic acid (saluamine), and the activation energy, calculated from thermogravimetric analysis (TGA) measurements, for this reaction was 47.7 (+/- 1.93) kcal/mol. The experimentally measured activation energy was well below the normal 59 +/- 4 kcal/mol needed for the cleavage of the C-N bond to form saluamine. This could possibly be explained by the weakening of the C-N bond through the I-effect of the furane ring and the delocalization of the electrons of the aniline nitrogen in the chlorosulfamoyl benzoic acid entity of furosemide. This decomposition of furosemide indicates the breaking of intramolecular bonds before those of intermolecular bonds (separation of individual furosemide molecules). Strong inter- and intramolecular bonds are a probable cause for the poor water solubility of furosemide because, when some of the inter- and intramolecular bonds that form part of the hydrogen bond network disappeared, as in the structurally related decomposition product saluamine, the aqueous solubility increased.

Diuretics↗
PubMed2000

Acute generalized exanthematic pustulosis (AGEP) in a patient treated with furosemide.

BACKGROUND: Although they appear more rarely than electrolyte disturbances, cutaneous reactions are important adverse effects of furosemide. This is particularly true for bullous skin eruptions, because they may be life-threatening. CASE REPORT: We describe a patient who developed acute generalized exanthematic pustulosis (AGEP) during treatment with furosemide. Because the patient had developed similar skin eruptions during treatment with furosemide years before, furosemide was considered the most likely cause of this reaction. The short period of time between exposure to furosemide and the appearance of the skin reaction, as well as a positive lymphocyte transformation test, suggest an immunological mechanism of the skin disease. CONCLUSION: AGEP is a possible cutaneous side effect of furosemide.

Aged↗
PubMed2006

Effect of timed semirecumbency and furosemide dosing on urinary sodium excretion in patients with compensated heart failure.

PURPOSE: The management of chronic cardiac failure, a salt-sensitive state, frequently includes administration of a loop diuretic to enhance urinary Na excretion. We hypothesized that a period of timed semirecumbency (vis-à-vis upright posture) would enhance the natriuresis that accompanies oral furosemide dosing in patients with compensated cardiac failure. METHODS: Four ambulatory patients with compensated chronic cardiac failure (NYHA Class III) of ischemic and nonischemic origin and systolic dysfunction (ejection fraction <35%), who were receiving a stable regimen of oral furosemide and angiotensin-converting enzyme inhibitor, were enrolled into the study. In the institution's Clinical Research Center, we monitored and compared urine flow rate (mL/min) and Na excretion rate (mEq/hr) in each patient in response to two different protocols. Protocol 1 consisted of an initial 90-minute period of bedrest followed by the patient's oral furosemide dose and 180 minutes of upright activity and a subsequent 90-minute period of bedrest. Protocol 2 was similar, with the exception that furosemide dosing was given after upright activity and immediately prior to the second period of bedrest. RESULTS: With each patient serving as his or her own control, both urine flow rate and urinary Na excretion rate were markedly increased when furosemide was given prior to bedrest as compared to its dosing prior to upright activity. CONCLUSIONS: In patients with compensated chronic cardiac failure, the natriuresis that accompanies oral furosemide dosing is enhanced when given just prior to a period of timed semirecumbency. This approach represents a more optimal use of this loop diuretic in patients with compensated heart failure.

Adult↗
PubMedDate not supplied

The effect of furosemide on the pulmonary transvascular fluid filtration rate.

Considerable controversy exists over the use of furosemide for the prevention of treatment of post traumatic respiratory insufficiency. The conflict revolves around the use of diuretic in a patient with this condition. There is some evidence that a nondiuretic effect of furosemide may be responsible for the reported improvement in lung function. We studied the response to furosemide of the pulmonary microvascular fluid filtration rate reflected in lung lymph flow (Qlym) in the normal lung. Using the unanesthetized sheep lung lymph preparation of Staub, we found a 30% decrease in Qlym after 80 mg furosemide. However, the majority of the decrease occurred within 15 min after injection when diuresis was just beginning. This response appeared to be due to a large decrease in pulmonary venous resistance, decreasing hydrostatic pressure. Protein flow (Qlym x lymph protein content) remained constant. Pulmonary artery pressure remained constant with left atrial pressure decreasing slightly. We have demonstrated that in the normal lung, furosemide significantly decreases the fluid filtration rate by a nondiuretic effect. Further studies of this response should help resolve the controversy over the indications for diuresis and center more attention on the actual mechanism of action of furosemide.

Animals↗
PubMed1992

Comparison of continuous versus intermittent furosemide administration in postoperative pediatric cardiac patients.

OBJECTIVE: To compare the effects of furosemide administered by intermittent iv infusion vs. continuous iv infusion on urine output, hemodynamic variables, and serum electrolyte concentrations. DESIGN: Prospective, randomized trial. SETTING: Pediatric ICU. PATIENTS: Postoperative pediatric cardiac patients. INTERVENTIONS: Patients were assigned to either the continuous iv infusion or the intermittent infusion groups. The intermittent group received 1 mg/kg iv of furosemide every 4 hrs to be increased by 0.25 mg/kg iv every 4 hrs to a maximum of 1.5 mg/kg iv if the urine output was less than 1 mL/kg.hr. The continuous infusion group received an initial furosemide dose of 0.1 mg/kg iv (minimum 1 mg) followed by an iv infusion rate of 0.1 mg/kg.hr of furosemide to be doubled every 2 hrs to a maximum of 0.4 mg/kg.hr if the urine output was less than 1 mL/kg.hr. MEASUREMENTS AND MAIN RESULTS: Demographic variables, fluids, electrolyte and inotropic requirements were the same in both groups. A significantly (p = .045) lower daily dose of furosemide (4.90 +/- 1.78 vs. 6.23 +/- 0.62 mg/kg.day) in the continuous iv infusion group produced the same 24-hr urine volume as that of the intermittent group. There was more variability in urine output in the intermittent group as well as more urinary losses of sodium (0.29 +/- 0.15 vs. 0.20 +/- 0.06 mmol/kg.day, p = .0007) and chloride (0.40 +/- 0.20 vs. 0.30 +/- 0.12 mmol/kg.day, p = .045). CONCLUSION: Furosemide administered by continuous iv infusion is advantageous in the post-operative pediatric patient because of a more controlled and predictable urine output with less drug requirement and less urinary loss in sodium and chloride.

Cardiac Surgical Procedures↗
PubMed1997

Role of kinins in basal and furosemide-stimulated renin secretion.

OBJECTIVE: There is evidence that kinins contribute to some of the renal, cardiovascular, and endocrine effects of the diuretic furosemide. The aim of the present study was to investigate the role of kinins in the regulation of renin secretion, blood pressure, and heart rate under resting conditions and after administration of furosemide. METHODS: The effects of icatibant, a potent, specific, and long-lasting bradykinin B2 receptor antagonist, on resting renin secretion, blood pressure, and heart rate, and on the responses of these variables to administration of furosemide, were investigated in conscious, chronically prepared rabbits. RESULTS: Injection of icatibant in doses of 0.1 and 1.0 mg/kg blocked the hypotensive response to intravenous injections of bradykinin completely. The lower dose of icatibant decreased plasma renin activity in some animals, but did not alter their blood pressure or heart rate. The higher dose suppressed resting plasma renin activity from 10.2 +/- 2.2 to 5.6 +/- 1.4 ng/ml/2 h (P < 0.01), without changing the blood pressure or heart rate. Injection of furosemide (2 mg/kg) caused a sustained increase i plasma renin activity from 6.7 +/- 1.6 to 15.9 +/- 3.3 ng/ml/2h (P < 0.01), a transient increase in mean arterial pressure from 72 +/- 3 to 78 +/- 3 mmHg (P < 0.05), and a sustained increase in heart rate from 228 +/- 8 to 253 +/- 6 bpm (P < 0.01). Neither dose of icatibant altered the cardiovascular and renin responses to furosemide. CONCLUSIONS: These results provide evidence that bradykinin B2 receptors participate in the regulation of resting renin secretion, but not in the renin secretory or heart rate responses to furosemide.

Animals↗
PubMed1987

Negative inotropic effects of furosemide in the isolated rabbit heart: a prostaglandin-mediated event.

Furosemide is an effective diuretic that initiates a rapid diuresis and peripheral vasodilatation through renal adenylate cyclase inhibition and prostaglandin synthesis. Recently, it has been shown to be associated with activation of the neurohumoral vasoconstrictor mechanism and a further compromise of left ventricular function in patients with heart failure. The present study was performed to investigate the direct effects of furosemide on myocardial performance in the isolated perfused rabbit heart. Furosemide (10(-3) M) caused a significant decrease in developed pressure as well as a similar fall in coronary perfusion pressure. Furosemide also decreased myocardial contractility when the coronary perfusion pressure was kept constant. The change in developed pressure but not the decrease in coronary perfusion pressure could be blocked by treatment with indomethacin. Furosemide did not antagonize rabbit cardiac membrane adenylate cyclase. Therefore, furosemide has a direct inhibitory effect on cardiac contractility that is related to prostaglandin synthesis.

Adenylyl Cyclases↗
PubMed2003

When could the administration of furosemide be avoided?

PURPOSE: The purpose of this study was to evaluate whether some parameters of the basic renogram allow one to omit the administration of furosemide in cases of hydronephrosis. MATERIALS AND METHODS: One hundred thirty-seven children (274 kidneys) referred for uni- or bilateral hydronephrosis were evaluated retrospectively. In all children additional furosemide challenges followed by postmicturition views were acquired because of unsatisfactory renal emptying. The patients were categorized into 2 groups according to the residual renal activity on the postmicturition view: those with good emptying (R-) of both kidneys, for which the administration of furosemide was considered of no influence, and those with partial or no emptying of at least 1 kidney (R+). The renogram parameters chosen for predicting R+ and R- were time to maximum (Tmax), output efficiency at 20 minutes (OE20), and normalized residual activity at 20 minutes (NORA20). For each parameter, the number of children was then calculated, for whom the administration of furosemide could have been omitted. RESULTS: A total of 112 children were categorized as R- and 25 as R+. The cutoff values for 100% negative predictive value of Tmax, OE20, and NORA20 were 4.5 minutes, 66%, and 1.45 respectively. Application of these cutoff values for the parameters yields, in retrospect, 6 (4%), 29 (21%), and 22 (16%) children respectively for whom administration of furosemide could have been omitted. CONCLUSION: On the basis of OE20 and NORA20, the administration of furosemide could have been omitted in a substantial number of patients, despite unsatisfactory renal emptying on the basic renogram.

Case-Control Studies↗
PubMed2004

Increasing the dose of furosemide in patients with azotemia and suspected obstruction.

Diuresis renography is widely used to distinguish obstructed from nonobstructed kidneys; however, the delivery of furosemide to its site of action in the loop of Henle is impaired in patients with azotemia. Consequently, the standard adult dose of 40 mg furosemide could be insufficient to generate an adequate diuretic response. This problem is illustrated by a patient with azotemia with bilateral nephrostomies who underwent Tc-99m MAG3 (mercaptoacetyltriglycine) diuresis renography with 40 mg furosemide to determine if his bilateral ureteral obstruction had resolved. The study showed findings typical for obstruction despite the fact that the patient could not have been obstructed because the nephrostomy tubes had not been clamped. When the study was repeated 6 days later with 80 mg furosemide and clamped nephrostomy tubes, there was good drainage bilaterally excluding obstruction. The nephrostomy tubes were removed and the patient's creatinine has subsequently remained stable for 3 years. In summary, this report illustrates the rationale for increasing the dose of furosemide in patients with azotemia referred for diuresis renography and shows how increasing the dose of furosemide could improve the diuretic response and minimize false-positive or indeterminate results.

Aged↗
PubMed1980

Increased urinary protein excretion after intravenous injection of furosemide in man.

The furosemide-induced increase in protein excretion, and its relations to 1) the size of protein molecules as reflected by three enzymes, and 2) glomerular filtration rate (GFR), plasma renin activity (PRA) and prostaglandin (PG) E2 and F2 alpha excretions were studied in 14 outpatients with normal renal function and 13 healthy males. Furosemide (120 mg) was given intravenously, and thereafter the protein excretion and the above parameters were monitored for 1--2 hours. In both groups, furosemide caused a transient increase in protein excretion. The excretion of the largest molecule, beta-glucuronidase, rose to 6.3-fold, while those of N-acetyl-beta-D-glucosaminidase and of the smallest molecule, alpha-amylase, increased by 91 and 37%, respectively. GFR increased, too, but markedly less than the protein excretion. PGE2 and PGF2 alpha excretions increased more than GFR and changed simultaneously with the excretion of proteins. Furosemide also caused a marked increase in PRA. This lasted, however, much longer than the rise in PG and protein excretion or GFR. The results suggest that the furosemide-induced increase in protein excretion is 1) related to the molecular size of proteins, 2) partly due to the rise in GFR, 3) simultaneous with the change in PG excretion. Our findings also agree with the view that furosemide causes changes in glomerular permeability.

Acetylglucosaminidase↗
PubMed1990

Atrial natriuretic factor, cyclic 3',5'-guanosine monophosphate and prostaglandin E2 in liver cirrhosis: relation to blood volume and changes in blood volume after furosemide.

Plasma concentrations of atrial natriuretic factor (ANF) and cyclic 3',5'-guanosine monophosphate (cGMP) were measured in 11 cirrhotic patients with ascites, 11 cirrhotic patients without ascites and 15 control subjects. The following were determined in 15 of the cirrhotic patients and in all the control subjects: blood volume (BV) and furosemide-induced changes in BV, plasma values of ANF, cGMP, angiotensin II (AII), aldosterone (Aldo), arginine vasopressin (AVP) and urinary excretion rates of cGMP, prostaglandin E2 (PGE2), water and sodium. Basal plasma levels of ANF and cGMP were higher in patients with cirrhosis than in controls, but were the same in both groups of cirrhotics (ANF: cirrhosis with ascites 12.7, without ascites 13.4, and in controls 5.8 pmol l-1 (medians); cGMP: 7.7, 7.4 and 4.3 nmol l-1, respectively). BV was less reduced after furosemide in the cirrhotic patients (6.0%) than in the healthy subjects (10.1%), but basal BV did not differ. Urinary sodium excretion rates after furosemide were significantly lower in the cirrhotic patients than in the controls. PGE2 excretion rate increased after furosemide in the cirrhotic patients (0.29 to 0.66 pmol min-1; P less than 0.01) but not in the controls (0.31 to 0.38 pmol min-1). After furosemide ANF and cGMP decreased slightly in both groups whereas AII and Aldo increased; AVP increased in the controls, but not in the cirrhotic patients. In conclusion, plasma values of ANF and cGMP are increased in liver cirrhosis both with and without ascites. This and the elevated PGE2 excretion after furosemide may be compensatory phenomena in order to facilitate renal sodium excretion.

Adult↗
PubMed1991

Furosemide-induced changes in plasma and blood volume of horses.

The effect of furosemide administration (1 mg/kg body weight, i.v.) on plasma and blood volumes in 6 intact and 4 splenectomized horses was measured using Evans blue dye dilution, hematocrit, and hemoglobin and plasma total solids concentrations. Body weight decreased by 33.6 +/- 3.3 and 33.7 +/- 0.8 g/kg 4 h after furosemide administration to intact and splenectomized mares, respectively. Plasma volume, estimated by Evans blue dye dilution, was reduced by 8.3 +/- 3.3% (mean +/- SE) 4 h after furosemide administration. The reduction in plasma volume was first detectable 5-10 min after furosemide administration and was greatest 15-30 min (13.0 +/- 0.8%) after dosing. This study demonstrates that furosemide produces significant and rapid reductions in plasma volume in horses. These decreases in plasma volume only partially resolve 4 h after furosemide administration.

Animals↗
PubMed1992

The pharmacokinetics and pharmacodynamics of furosemide in the anaesthetized dog.

The correlation between pharmacokinetics and dynamics of furosemide was investigated in anaesthetized dogs. After intravenous administration (i.v.) of furosemide (5 mg/kg), the plasma concentration declined rapidly with bioexponential decay. The half-life (t1/2 beta) of the late phase of elimination was 0.931 +/- 0.187 h and the apparent volume of distribution at steady state was 0.25 +/- 0.043 l/Kg. The total clearance (Cltot) was 0.435 +/- 0.031 l/h/kg, in which the renal clearance was 0.260 +/- 0.020 (about 60% of Cltot). The change in rate of urinary excretion of furosemide was similar to the plasma concentration decay curve. The diuretic effect of furosemide was accompanied by an extreme increase in the excretion rate of sodium and chloride, but not potassium. The relationships between the diuretic response and the plasma concentration or the urinary excretion rate of furosemide was depicted by sigmoidal dose-response curves in both cases. The half-maximum effect was obtained at 1.5 micrograms/ml of plasma concentration or at 80 micrograms/min of excretion rate of furosemide.

Anesthesia, Intravenous↗
PubMed1988

Effects of furosemide on renal haemodynamics and proximal tubular sodium reabsorption in conscious rats.

1. The effects of furosemide given as constant i.v. infusion (7.5 mg kg-1 h-1) or bolus injections (0.5, 7.5 and 120 mg kg-1) on renal haemodynamics and proximal tubular Na reabsorption were studied in conscious water diuretic rats. The clearance of Li (CLi) was used as marker for Na delivery from the proximal tubules, and clearance of [14C]-tetraethylammonium (CTEA) and [3H]-inulin (CIn) as markers for renal plasma flow (RPF) and glomerular filtration rate (GFR), respectively. 2. Furosemide caused a transient increase of RPF and GFR followed by a secondary decrease below baseline levels; the latter could in part be counteracted by volume replacement. The filtration fraction (FF = GFR/RPF) was not significantly changed by furosemide. Fractional proximal Na excretion (CLi/CIn) was significantly increased by all doses of furosemide independent of changes in RPF, GFR and FF. 3. The peak diuretic/natriuretic effect of furosemide was markedly potentiated by volume replacement, probably due to prevention of antinatriuretic mechanisms triggered by volume depletion. 4. It is concluded that following i.v. furosemide administration there is a biphasic change in renal haemodynamics in conscious, restrained rats, and that the inhibition of proximal Na reabsorption, as manifested by changes in fractional Li excretion, is not likely to be due to changes in total renal haemodynamics.

Animals↗