Direct Effect Of Furosemide Research Articles

Furosemide depresses the presynaptic fiber volley and modifies frequency-dependent axonal excitability in rat hippocampus.

The loop diuretic furosemide is known to have anticonvulsant effects, believed to be exerted through blockade of glial Na+-K+-2Cl- cotransport causing altered volume regulation in brain tissue. The possibility that direct effects of furosemide on neuronal properties could also be involved is supported by previous observations, but such effects have not been thoroughly investigated. In the present study we show that furosemide has two opposing effects on stimulus-induced postsynaptic excitation in the nonepileptic rat hippocampal slice: 1) an enhancement of e-s coupling, which depended on intact GABAA transmission and was partially mimicked by selective blockade of K+-2Cl- cotransport, and 2) a decrement of field excitatory postsynaptic potentials. The balance between these effects varied, depending on the amount of synaptic drive. In addition, the compound action potential (fiber volley) recorded from the stimulated Schaffer collateral axons in stratum radiatum showed a progressive decrease during perfusion of furosemide. This effect was activity-independent, was mimicked by the stilbene derivative DIDS, and could be reproduced on fiber volleys in the alveus. Furosemide also reduced the initial enhancement of the fiber volley observed during trains of high-frequency stimulation (HFS). Results of hyperosmotic expansion of the extracellular volume, with 30 mM sucrose, indicated that both the induction and antagonism of the HFS-induced enhancement were independent of signaling via the extracellular space. Furosemide caused an increased decay of paired-pulse-induced supranormal axonal excitability, which was antagonized by ZD7288. We conclude that furosemide decreases axonal excitability and prevents HFS-induced hyperexcitability via mechanisms downstream of blockage of anion transport, which could include hyperpolarization of axonal membranes.NEW & NOTEWORTHY This study shows that the anion transporter antagonists furosemide and DIDS cause a marked decrease of axonal excitability in rat hippocampal CA1 region and prevent the induction of activity-dependent hyperexcitability in Schaffer collateral axons. The data are consistent with direct effects on axonal membrane properties. We also find that activity-dependent enhancement and depression of axonal excitability can be modified independently, suggesting that these events are governed by different underlying processes.

Furosemide stimulation of parathormone in humans: role of the calcium-sensing receptor and the renin-angiotensin system.

Interactions between sodium and calcium regulating systems are poorly characterized but clinically important. Parathyroid hormone (PTH) levels are increased shortly after furosemide treatment by an unknown mechanism, and this effect is blunted by the previous administration of a calcimimetic in animal studies. Here, we explored further the possible underlying mechanisms of this observation in a randomized crossover placebo-controlled study performed in 18 human males. Volunteers took either cinacalcet (60 mg) or placebo and received a 20 mg furosemide injection 3 h later. Plasma samples were collected at 15-min intervals and analyzed for intact PTH, calcium, sodium, potassium, magnesium, phosphate, plasma renin activity (PRA), and aldosterone up to 6 h after furosemide injection. Urinary electrolyte excretion was also monitored. Subjects under placebo presented a sharp increase in PTH levels after furosemide injection. In the presence of cinacalcet, PTH levels were suppressed and marginal increase of PTH was observed. No significant changes in electrolytes and urinary excretion were identified that could explain the furosemide-induced increase in PTH levels. PRA and aldosterone were stimulated by furosemide injection but were not affected by previous cinacalcet ingestion. Expression of NKCC1, but not NKCC2, was found in parathyroid tissue. In conclusion, our results indicate that furosemide acutely stimulates PTH secretion in the absence of any detectable electrolyte changes in healthy adults. A possible direct effect of furosemide on parathyroid gland needs further studies.

Furosemide alters nonlinear capacitance in isolated outer hair cells

The outer hair cell (OHC) from the organ of Corti plays a crucial role in hearing through its unique voltage-dependent mechanical responses. Furosemide, one of the loop diuretics, disrupts normal cochlear function. Here we report on direct effects of furosemide on OHC motility-related, voltage-dependent capacitance using the whole-cell patch-clamp technique. Extracellularly applied furosemide reversibly shifted the voltage at peak capacitance ( V pkC m ) to positive levels. The shift, whose maximum approached 90 mV, evidenced a Hill coefficient of 1.5 and K 1/2 of 10 mM. Changes in the magnitude of nonlinear capacitance were not fully reversible. While it is clear that the overwhelming effect of furosemide on hearing results via its effects on the endolymphatic potential, the present results indicate that furosemide directly alters OHC motility and may, in part, contribute to sensory dysfunction.

Effects of hydrochlorothiazine and furosemide diuretics on human bone marrow stromal osteoprogenitor cells

Thiazide diuretics have been shown to decrease bone loss and improve bone mineral density, while long-term furosemide therapy has been suggested to decrease bone mineral content. However, the direct effects of these diuretics on osteoblastic cells are not well established. Some investigators have reported direct effects of thiazides on osteoblastic cells but the results remain controversial, and there are few data about the direct effect of furosemide on osteoblastic cells. We investigated the effects of hydrochlorothiazide (HCTZ) and furosemide on proliferation, alkaline phosphatase activity, osteocalcin, and interleukin-6/interleukin-11 (IL-6/IL-11) secretion in cultured normal human bone marrow stromal osteoprogenitor cells (hBMSCs). Treatment with HCTZ or furosemide for 24 hours in the concentration range of 10(-6) to 10(-4) mol/L did not affect 3H-thymidine incorporation in hBMSCs. Cellular alkaline phosphatase activity and osteocalcin production were not changed significantly by treatment with HCTZ or furosemide (up to 10(-4) mol/L) during culture. There was also no significant difference in IL-6 and IL-11 production in hBMSCs. These results suggested that HCTZ or furosemide had no significant direct effect on proliferation, alkaline phosphatase activity, osteocalcin, and IL-6/IL-11 production in hBMSCs, and the effects of these diuretics on bone mass may be related to the indirect action on calcium balance.

Mechanisms of renal vasoconstriction following furosemide in conscious rats.

Regional hemodynamics following intravenous injection of furosemide were studied in conscious rats instrumented with Doppler flowprobes. Furosemide caused a dose-dependent acute (within 3 min) transient increase in renal resistance (RR) followed by a later generalized vasoconstriction in the renal, mesenteric and hindquarter (HQR) vascular bed. With in vitro experiments a possible direct effect of furosemide on renal artery segments was excluded. The acute rise in RR was partly (approximately 40%) attenuated by pretreatment with phentolamine or prazosin, but not prevented by renal denervation, volume repletion or pretreatment with captopril, losartan, indomethacin, aminophylline, nifedipine, or a vasopressin V1A-receptor-antagonist. However, the acute renal vasoconstriction was absent in water diuretic rats. The later vasoconstriction was blunted by captopril (RR+HQR), losartan (RR) and phentolamine (HQR) pretreatment. We conclude that the later generalized vasoconstriction following furosemide involves regional specific stimulation of angiotensin II and alpha-adrenoceptors. The mechanism of the acute renal vasoconstriction could not be fully determined. Because of its absence in water diuretic rats, its rapid onset, transient nature and relative insensitivity for pharmacological tools in euvolemic rats, the acute increase in RR following furosemide may be caused by cell swelling as a result from dissipation of the renal medullary gradient.

Furosemide-Induced Hyperglycaemia: The Implication of Glycolytic Kinases

Hyperglycaemia is a well known adverse effect of therapy with diuretics. In adipose tissue, hydrochlorothiazide and furosemide inhibit the rate of glucose transport. In skeletal muscle, furosemide decreases the rate of glucose phosphorylation and glycolysis. However, whether furosemide has any direct effect on the activities of any of the glycolytic enzymes is not known. In the present study, the effects of furosemide on the activities of the hexokinase, phosphofructokinase and pyruvate kinase were examined. Pieces of skeletal muscle (quadriceps) and liver were obtained from 10 non-diabetic subjects during surgery. Tissues were homogenized and the activities of the enzymes were measured in the presence or absence of furosemide (0-1.5 mM). Furosemide inhibited the activity of all three key glycolytic enzymes. The concentration of furosemide required to inhibit phosphofructokinase in muscle was lower than that required to inhibit the activity of this enzyme in the liver or to inhibit the activities of hexokinase and pyruvate kinase in both muscle and liver. These direct effects of furosemide may contribute to the decrease in glucose utilisation following therapy with this and similar agents in man.

Furosemide Differentially Relaxes Airway and Vascular Smooth Muscle in Fetal, Newborn, and Adult Guinea Pigs

Furosemide, an inhibitor of Cl-dependent Na+,K+ cotransport, is the most frequently used diuretic in newborns. Recently, furosemide was also demonstrated to decrease bronchial hyper-responsiveness in adults, although little is known about the direct effect of furosemide on smooth muscle of immature animals. This in vitro study was designed to determine the action of furosemide on airway and vascular smooth muscle during ontogeny. Extrathoracic trachea (ET), main stem bronchi, main pulmonary artery, and thoracic aorta ring segments from fetal, newborn, and adult Hartley albino guinea pigs were suspended in HEPES solution for measurement of isometric tension. Furosemide (30 or 300 microM) was administered after preconstriction with an ED35-70 concentration of histamine or acetylcholine for airway and ED40-100 concentration of norepinephrine for vessels. Furosemide (30 microM) caused significant relaxation of airway smooth muscle at all ages. After histamine-induced preconstriction, fetal airway segments exhibited greatest relaxation (183 +/- 28%), with newborn airway demonstrating 123 +/- 15% relaxation and modest relaxation seen in adults (40 +/- 4%). This pattern was similar for both ET and bronchus and appeared greater for histamine compared with ACh preconstriction. Epithelial removal slightly enhanced relaxation. Furosemide also relaxed pulmonary artery segments, but at a 10-fold higher concentration. In striking contrast to the pattern seen in airway, adult pulmonary artery relaxed more than newborn and newborn, more than fetus. Cyclooxygenase blockade and endothelium removal did not change pulmonary artery relaxation. Furosemide did not significantly relax aorta after NE preconstriction. Taken together, these results suggest that furosemide may be more effective in relaxing airway compared with vascular smooth muscle, and the ontogeny of these responses indicates a greater efficacy and selectivity in airways of immature animals.

Direct effects of furosemide and amiloride on the perfused and ischaemic rat heart.

The present study was undertaken in order to assess direct effects of furosemide and furosemide plus amiloride upon the perfused and ischaemic isolated rat heart. Furosemide in concentrations ranging between 4-400 mg/l in the perfusate increased coronary flow in a concentration dependent manner. There was no evidence for a negative inotropic effect of furosemide. However, very high doses of furosemide (400 mg/l) decreased the post-ischaemic values of left ventricular developed pressure, coronary flow rate, adenosine triphosphate, creatine phosphate and potassium, and increased the myocardial content of calcium and sodium. Furosemide 4 mg/l and 40 mg/l had no effect on post-ischaemic parameters compared to the control group except that furosemide 40 mg/l increased the recovery of coronary flow. Although amiloride 13.3 mg/l alone did not affect post-ischaemic recovery, the addition of this dose to furosemide 400 mg/l improved the post-ischaemic recovery of left ventricular developed pressure, coronary flow rate and adenosine triphosphate. The myocardial content of magnesium and potassium was higher indicating protection of amiloride by its magnesium- and potassium-sparing properties opposing ischaemic losses aggravated by the exposure to furosemide.

Negative Inotropic Effects of Furosemide in the Isolated Rabbit Heart

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.

The effect of lung edema on pulmonary vasoactivity of furosemide

Previous data suggest that furosemide improves gas exchange in pulmonary edema by preferential perfusion of nonedematous lung units. To test whether this is a direct effect of furosemide on the pulmonary vasculature as opposed to a secondary phenomenon resulting from the known peripheral effects of this drug, the effect of furosemide on the pressure-flow characteristics of the pulmonary vasculature was studied in six isolated perfused canine lungs with different degrees of gravimetrically determined edema. Furosemide shifted the pressure-flow curve by decreasing the mean intercept or average closing pressure of the pulmonary vascular bed from 13.8 ± 5.3 to 9.5 ± 5.4 cm H 2O and the zero-flow critical closing pressure from 9.3 ± 4.3 to 4.7 ± 3.5 cm H 2O ( P < 0.05). The slopes of these curves did not change between control and furosemide treatment. The decrease in intercept and the decrease in zero-flow critical closing pressures were closely correlated with the increase in edema ( r = −0.895 for average closing pressure and r = −0.928 for critical closing pressure) ( P < 0.05). Furosemide doubled the pulmonary blood flow in the isolated lobe for the same driving pressure and the greater the amount of lobar edema the less pronounced was this furosemide-associated increase in blood flow. This direct effect of furosemide on the pulmonary vasculature could explain the improved gas exchange seen before a decrease in pulmonary edema, since this pulmonary vasoactivity would result in preferential perfusion of nonflooded alveolar units.

Increased pulmonary vascular permeability following acid aspiration.

The effect of hydrochloric acid aspiration on transvascular fluid and protein flux and lung water content was studied in 21 anesthetized dogs. We measured steady-state lung lymph flow, pulmonary arterial and left atrial pressures, and the concentration of total protein and albumin in both lymph and plasma after intratracheal instillation of 2 ml/kg 0.1 N HCl. Acid injury produced a twofold increase in lung lymph flow and lymph protein clearance when compared with control. This indicated an increase in pulmonary microvascular permeability. In dogs given 25 g concentrated human albumin and 1 mg/kg furosemide 10 min after the acid injury, the acid-induced increase in fluid filtration was prevented. However, the decrease in fluid filtration was not attributed to an increase in the transvascular protein osmotic pressure gradient but to a more direct effect of furosemide. Treatment with furosemide alone prevented the increase in lung lymph flow induced by acid injury, whereas albumin alone did not. In all acid-injured animals there was an increase in lung water when compared wtih control. Therefore acid aspiration produced localized areas of damage to filtration vessels that lead to increased leakage of protein and water. Furosemide treatment prevented much of this increased fluid and protein flux by an undefined mechanism.