Effect of frusemide on the reactivity of rat portal vein

Effects of inhibition of the Na+/K+/2Cl− cotransporter on myogenic and angiotensin II responses of the rat afferent arteriole

The Na+/K+/2Cl− cotransporter (NKCC) plays diverse roles in the kidney, contributing sodium reabsorption and tubuloglomerular feedback (TGF). However, NKCC is also expressed in smooth muscle and inhibitors of this transporter affect contractility in both vascular and nonvascular smooth muscle. In the present study, we investigated the effects of NKCC inhibitors on vasoconstrictor responses of the renal afferent arteriole using the in vitro perfused hydronephrotic rat kidney. This preparation has no tubules and no TGF, eliminating this potential complication. Furosemide and bumetanide inhibited myogenic responses in a concentration-dependent manner. Bumetanide was ∼20-fold more potent (IC50 1.0 vs. 20 μmol/l). At 100 and 10 μmol/l, furosemide and bumetanide inhibited myogenic responses by 72 ± 4 and 68 ± 5%, respectively. The maximal level of inhibition by bumetanide was not affected by nitric oxide synthase inhibition (100 μmol/l NG-nitro-l-arginine methyl ester). However, the time course for the dilation was slowed (from t1/2 = 4.0 ± 0.5 to 8.3 ± 1.7 min, P = 0.04), suggesting either a partial involvement of NO or a permissive effect of NO on relaxation kinetics. Bumetanide also inhibited ANG II-induced afferent arteriolar vasconstriction at similar concentrations. Finally, NKCC1, but not NKCC2, expression was demonstrated in the afferent arteriole by RT-PCR and the presence of NKCC1 in afferent arteriolar myocytes was confirmed by immunohistochemistry. In concert, these results indicate that NKCC modulation is capable of altering myogenic responses by a mechanism that does not involve TGF and suggest a potential role of NKCC1 in the regulation of vasomotor function in the renal microvasculature.

Only weak vasorelaxant properties of loop diuretics in isolated resistance arteries from man, rat and guinea pig

Besides their diuretic action, loop diuretics may induce a rapid vasodilator effect that contribute to their short-term therapeutic properties. We examined the effects of furosemide (10(-6)-10(-3) mol l(-1)) in comparison with bumetanide (10(-6)-10(-4) mol l(-1)) on isolated resistance arteries from rat and guinea pig mesentery and human subcutaneous fat, and investigated the mechanism of the acute direct vasorelaxant action on an isometric microvascular myograph. Both loop diuretics induced concentration-dependent relaxation of resistance vessels irrespective of membrane potential. The maximal effect of furosemide was greatest in rat and least in human arteries. Both diuretics caused a rightward shift in the concentration-response curve to extracellular Ca(2+). Incubation with indomethacin (2 x 10(-5) mol l(-1)) or mechanical removal of the endothelium did not inhibit the loop diuretic-induced relaxation. At high concentrations (10(-4)-10(-3) mol l(-1)) loop diuretics exert only weak direct relaxant effects on isolated human subcutaneous resistance arteries compared to the vasorelaxant effects in rat and guinea pig mesenteric vessels.

Decreased blood pressure and vascular smooth muscle tone in mice lacking basolateral Na(+)-K(+)-2Cl(-) cotransporter

The basolateral Na(+)-K(+)-2Cl(-) cotransporter (NKCC1) functions in the maintenance of cellular electrolyte and volume homeostasis. NKCC1-deficient (Nkcc1(-/-)) mice were used to examine its role in cardiac function and in the maintenance of blood pressure and vascular tone. Tail-cuff measurements demonstrated that awake Nkcc1(-/-) mice had significantly lower systolic blood pressure than wild-type (Nkcc1(+/+)) mice (114.5 +/- 2.2 and 131.8 +/- 2.5 mmHg, respectively). Serum aldosterone levels were normal, indicating that extracellular fluid-volume homeostasis was not impaired. Studies using pressure transducers in the femoral artery and left ventricle showed that anesthetized Nkcc1(-/-) mice have decreased mean arterial pressure and left ventricular pressure, whereas myocardial contraction parameters were not significantly different from those of Nkcc1(+/+) mice. When stimulated with phenylephrine, aortic smooth muscle from Nkcc1(+/+) and Nkcc1(-/-) mice exhibited no significant differences in maximum contractility and only moderate dose-response shifts. In phasic portal vein smooth muscle from Nkcc1(-/-) mice, however, a sharp reduction in mechanical force was noted. These results indicate that NKCC1 can be important for the maintenance of normal blood pressure and vascular tone.

Frusemide inhibits angiotensin II-induced contraction on human vascular smooth muscle

AIMS

Frusemide is widely used in the treatment of acute pulmonary oedema, chronic congestive heart failure and, to a lesser degree, in the treatment of hypertension. Evidence suggests that frusenuide exerts an anti-vasoconstrictor effect independent of its diuretic properties. Since angiotensin II is a highly potent vasoconstrictor involved in the pathophysiology of these diseases, we have investigated the effect of frusemide on the contraction elicited by angiotensin II on human internal mammary artery (IMA) and saphenous vein (SV).

METHODS

Rings of IMA and SV were suspended for isometric tension recording in organ baths. Concentration-response curves to angiotensin II were performed in the absence (control) or in the presence of frusemide (10(-6) to 10(-3) M). In addition, the effect of frusemide was evaluated after cyclooxygenase inhibition by indomethacin (10(-6) M) and was compared with those of the other loop diuretic bumetanide (10(-4) M).

RESULTS

Frusemide induced a concentration-dependent decrease of the contraction elicited by angiotensin II on IMA and SV. On both vessels, the inhibitory effect on the maximal contraction to angiotensin II was significant with concentrations of frusemide from 10(-5) to 10(-3) M. Angiotensin II potency (pD2) was only reduced by 10(-3) M frusemide. The effect of frusemide was not altered in the presence of indomethacin. Bumetanide was less potent than frusemide in inhibiting angiotensin II-induced contractions in both IMA and SV.

CONCLUSIONS

Frusemide, at concentrations in the therapeutic range (10(-5) M), inhibits angiotensin II-induced contraction on human isolated IMA and SV. This inhibitory effect is cyclooxygenase independent and appears mediated, at least in part, by inhibition of Na+/K+/2Cl- symport. Reduction in the vasoconstrictor effect of angiotensin 1 may be involved in the therapeutic efficacy of frusemide.

No evidence of a direct venodilatory effect of furosemide in healthy human subjects

The present study was undertaken to examine whether furosemide, a loop diuretic, has a direct venodilatory effect in healthy male subjects. Furosemide, or amrinone, an inotropic agent with a vasodilatory action, was infused into a dorsal hand vein that had been preconstricted by phenylephrine. The diameter of the vein was measured by a linear variable differential transformer. Venodilation was observed during the infusion of amrinone, but such a response was not detected with furosemide. These findings do not support the hypothesis that furosemide has a direct venodilatory effect in healthy human subjects.

Effect of frusemide, ethacrynic acid and indanyloxyacetic acid on spontaneous Ca-activated currents in rabbit portal vein smooth muscle cells

1. The effect of frusemide, ethacrynic acid and indanyloxyacetic acid was investigated on spontaneous calcium-activated chloride (ICl(Ca)) and potassium currents (IK(Ca)) in rabbit portal vein cells with the perforated patch technique. 2. Frusemide (0.3-1.0 x 10(-3) M) reduced the amplitude of spontaneous transient inward chloride currents (STICs) in a concentration-dependent manner. The degree of inhibition on STIC amplitude was similar between -50 and +30 mV and frusemide did not alter the STIC reversal potential (Erev). 3. The voltage-dependent exponential decay of STICs, which is thought to represent closure of chloride channels, was not altered by frusemide. 4. The amplitude and frequency of spontaneous potassium outward currents (STOCs) were not altered by frusemide. Since both STICs and STOCs are activated by calcium released from intracellular stores these data indicate that frusemide may block directly ICl(Ca). 5. Ethacrynic acid (2-5 x 10(-4) M) decreased the amplitude of STICs in a concentration-dependent manner by a similar amount at potentials of -50 to +30 mV but did not alter the STIC Erev. However, these concentrations of ethacrynic acid also reduced STOC amplitude and 5 x 10(-4) M ethacrynic acid evoked a sustained outward current in most cells at 0 mV; thus ethacrynic acid has a more complex action than simple block of ICl(Ca). 6. Indanyloxyacetic acid reduced both STIC amplitude and decay time without affecting STOCs and thus also seems to inhibit directly ICl(Ca). It is discussed whether block of ICl(Ca) mediates the vasodilator effect of these agents.

Immediate hemodynamic response to furosemide in patients undergoing chronic hemodialysis

To evaluate the effect of furosemide on cardiovascular hemodynamics in patients with end-stage renal failure, we studied ten patients undergoing hemodialysis three times a week. Arterial pressure, heart rate, and cardiac output (indocyanine green dye) were measured in triplicate; total peripheral resistance and central blood volume were calculated by standard formulas. Hemodynamics were determined at baseline and 5, 10, 15, and 30 minutes after intravenous (IV) bolus injection of furosemide 60 mg. Furosemide produced a decrease in central blood volume of -13% +/- 2.2% from pretreatment values (P less than .01) that was most pronounced five minutes after injection, together with a fall in cardiac output (from 6.76 +/- 0.59 to 6.17 +/- 0.52 L/min, P less than .10). Stroke volume decreased with a maximum fall occurring after 15 minutes (from 84 +/- 7 to 79 +/- 7 mL/min, P less than .05), and total peripheral resistance increased (from 15.8 +/- 2.1 to 17.8 +/- 2.3 units, P less than .05) after furosemide. Arterial pressure and heart rate did not change. The decrease in central blood volume reflects a shift of the total blood volume from the cardiopulmonary circulation to the periphery, suggesting dilation of the peripheral venous bed. Thus, even in patients undergoing hemodialysis, furosemide acutely decreases left ventricular preload by venous dilation and should therefore prove to be beneficial in acute volume overload.

Furosemide vasodilates the canine gastrointestinal tract

The ability of furosemide to induce vasodilation in the canine gastrointestinal system was studied by quantitative flowmetry. Blood flow and conductance increased maximally by 60 per cent in the stomach and duodenum and by 80 per cent in the small and large intestine. Vasodilation was evident at 2.4 mg/kg furosemide and higher. The onset of vasodilation occurred at 24 to 30 seconds and was maximal at 36 seconds in the stomach, at 66 seconds in the duodenum, at 78 to 84 seconds in the small intestine, and at 90 seconds in the large intestine. Hepatic arterial, splenic, and renal blood flows were unchanged. Simultaneous arteriovenous sampling from the small intestine indicated that the increased blood flow was not associated with increased O2 consumption. However, CO2 addition to the venous effluent decreased by 70 per cent. These data indicate that furosemide has a vasodilatory action on the gastrointestinal tract due either to a delayed effect on the vascular smooth muscle cell or on anaerobic bowel wall metabolism. The CO2 data are compatible with, but do not prove, stimulation of secretion of HCO3- by the intestinal mucosa.

Divergent effects of propranolol and furosemide pretreatment on acute cardiomyopathy induced by minoxidil in beagle dogs

Previous studies have shown that oral administration of minoxidil on 2 consecutive days produces an increase in heart rate and myocardial necrosis in Beagle dogs. Propranolol treatment (1.0 or 3.0 mg/kg every 8 h) did not abolish tachycardia and did not alter the incidence or severity of minoxidil-induced necrosis. In the present studies, pretreatment with either furosenmide (10 mg/kg) or hydrochlorothiazide (250 mg/kg) reduced serum potassium levels. However, only furosemide (for 11 days) reduced significantly the incidence of minoxidil-induced necrosis; only 2 of 10 animals (20%) developed myocardial lesions compared to 11 of 14 (79%) in the non-treated group. The incidence and severity of lesions in hearts from animals treated with furosemide for 3 days or hydrochlorothiazide for 11 days were essentially the same as in animals given minoxidil alone. Thus, furosemide, under certain conditions, can reduce the incidence of acute ventricular lesions induced by minoxidil.

Furosemide-induced vasodilation: importance of the state of hydration and filtration

The circumstances under which furosemide increases renal blood flow was examined in mongrel dogs as it may relate to a tubuloglomerular feedback mechanism. Two maneuvers, desoxycorticosterone (DOCA) plus salt treatment and inhibition of tubular fluid flow, were used in the dogs to evaluate the renal vascular effects of furosemide because these maneuvers have been reported to blunt the tubuloglomerular feedback in micropuncture studies. In addition, we also used two structurally different nonsteroidal antiinflammatory drugs to assess the importance of prostaglandins to achieve furosemide's renal vasodilatation. Furosemide (5 mg/kg, i.v.) increased renal blood flow in volume-depleted animals from a baseline flow of 141 +/- 28 ml/min to a maximum of 176 +/- 35 ml/min at 6 min after furosemide administration. If the animals were pretreated with a high-salt diet and i.m. DOCA for 5 days, furosemide administration produced no renal vascular effects but still caused a large diuresis, and these dogs still had a responsive renal vascular bed to infused prostaglandin E2. In addition, kidneys rendered non-filtering in volume-depleted animals had no renal vascular response to furosemide. Volume-depleted animals, pretreated with either indomethacin or sodium meclofenamate, did not have a renal vascular response to furosemide although they did have a diuretic response and a responsive renal vasculature to prostaglandin E2. From our data, we hypothesize that the renal vascular response to furosemide is secondary to a tubular mechanism mediated by a vasodilatory prostaglandin. Because furosemide has been shown to disrupt the tubuloglomerular feedback mechanism, and the two maneuvers, DOCA plus salt treatment and lack of filtration, blunt the tubuloglomerular feedback response as well as inhibit the renal vascular response to furosemide, we further hypothesize that furosemide-induced renal vasodilation may be secondary to the disruption of an active tubuloglomerular feedback mechanism.

The effects of long term oral treatment with indapamide on the development of DOCA-salt hypertension in rats: vascular reactivity studies

The onset of DOCA-salt hypertension in male Sprague-Dawley rats was prevented during 11 weeks of oral treatment with indapamide (0.5, or 10.0 mg/kg) or propranolol (60 mg/kg) administered in the diet. The body weights of the indapamide treated groups were significantly (P < 0.01) greater, at weeks 4, 5, 6, 7 and 11, while the body weights and food intake of the propranolol treated group were significantly (P < 0.05) lower at week 11, than the control group. A significant reduction in heart wet weight (P < 0.001) was measured in the indapamide treated animals only. No significant diuresis nor natriuresis was measured in any group during week 11 of treatment. When all groups were subjected to an increased salt load, four weeks after cessation of drug treatment only the indapamide (10 mg/kg) treated animals failed to show an increased blood pressure. Vascular reactivity studies carried out six weeks after termination of drug treatment, indicated a significant (P < 0.01) reduction in pressor activity elicited by electrical stimulation of the entire sympathetic outflow in indapamide (10 mg/kg) treated pithed rats. No significant difference in the pressor activity elicited by noradrenaline (5 x 10(-8) - 5 x 10(-6) g/kg, i.v.) or tyramine (10(-5) - 5 x 10(-5) g/kg i.v.) was observed in any treatment group. In conclusion, chronic oral treatment with indapamide or propranolol, prevented the onset of DOCA-salt hypertension in rats. A long lasting antihypertensive action of indapamide involving the sympathetic nervous system is also indicated.

Furosemide exhibits physicochemical properties similar to prostaglandins and interferes with their bioassay

The parallel pharmacological assay system has been of inestimable value in the identification and quantification of prostaglandins. A greater degree of specificity is conferred on the bioassay system by the preparative techniques of extraction and chromatography, for substances which might interfere with the assay of prostaglandins are usually eliminated by these procedures. It would be highly unlikely for a substance to survive the extraction procedure, to exhibit chromatographic properties similar to the prostaglandins and to interfere with their bioassay. We report here such an occurrence. Thus, furosemide not only survived the acidic lipid extraction, but, in addition, it exhibited chromatographic properties identical to those of the prostaglandins of the E series and finally, furosemide, at a dose which in and of itself was without effect on the assay tissues, inhibited the responses to prostaglandins. The quantification of prostaglandins by radioimmunoassay was, on the other hand, not altered by the presence of furosemide. This latter method appears to be the one of choice when interrelations between prostaglandins and furosemide are being examined.

Changes in vascular reactivity in experimental hypertensive animals following treatment with indapamide

Indapamide at doses of 8–16 mg kg−1 day−1, orally, lowered arterial blood pressure (9–26 mm Hg) in conscious renal hypertensive cats during a two week treatment period. The antihypertensive effect was sustained for 5–7 h after dosing and was not accompanied by reflex tachycardia. Antihypertensive responses to injection of clonidine (20 μg, i.c.v.) were significantly enhanced one week after the completion of indapamide treatment but had returned to normal two weeks later. In DOCA/saline hypertensive rats, administration of indapamide 10 mg kg−1 day−1, orally, or hydrochlorothiazide, 5 mg kg−1 day−1, intraperitoneally, for 10 days produced similar falls in blood pressure (40–45 mm Hg) as measured by an indirect method. Pressor responses to intravenous noradrenaline or tyramine or electrical stimulation of the sympathetic outflow in the pithed rat preparation were much reduced by pretreatment with indapamide (10 mg kg−1, orally) for 10 days. However, cardiovascular reactivity was unaffected by hydrochlorothiazide pretreatment (5 mg kg−1 day−1, i.p.). Isolated perfused mesenteric artery***/preparations from indapamide-treated rats showed no changes in reactivity to noradrenaline, 5-hydroxytryptamine or adenosine-5′-triphosphate from those of control DOCA/saline hypertensive rats. Isolated portal veins from rats pretreated with indapamide showed contractile responses to noradrenaline similar to those of control animals although the frequency of spontaneous contractions was reduced in the former group. The results support a vascular site of action for indapamide and suggest a mode of action different from that of hydrochlorothiazide.

Actions of prolactin and frusemide on heart rate and rhythm

Rat hearts with coronary circulations perfused by the Langendorff technique were studied. Recordings were made of the electrical and mechanical activity. Once the rate and rhythm of each heart and stabilized it was perfused with Ringer-Locke solution for 90 minutes; frusemide (40 mug/ml) was added to the perfusate during the last 30 minutes of this period. Eighteen experiments were performed-six controls, six in which prolactin at a concentration of 50 ng/ml was added to the perfusate for the whole 90 minutes, and six in which a prolactin concentration of 200 ng/ml was used.With the controls heart rate and rhythm remained steady, but there was a slow decline in amplitude of the contraction. With a prolactin concentration of 50 ng/ml the heart rate rose to about 40% above control during the first hour and after an initial sharp increase the contraction amplitude declined more rapidly than in the controls. The prolactin concentration of 200 ng/ml produced a decline of about 25% in heart rate over the first hour and amplitude behaved much as in the controls. Frusemide had no clear effect on the rate of beating of the controls, but it tended to reverse both the acceleration produced by 50 ng/ml prolactin and the slowing produced by the higher dose. Both the doses of prolactin consistently caused disturbances of rhythm. These effects occur at concentration of prolactin found in human plasma in various pathophysiological conditions.