Role of EDHF in the vasodilatory effect of loop diuretics in guinea-pig mesenteric resistance arteries

A randomized, controlled trial of the renal effects of ultrafiltration as compared to furosemide in patients with acute decompensated heart failure

OBJECTIVES

This study was designed to evaluate the consequences of ultrafiltration (UF) and standard intravenous diuretic (furosemide) therapy on glomerular filtration rate (GFR) and renal plasma flow in patients with acute decompensated heart failure.

BACKGROUND

It has been hypothesized that treatment with diuretics may worsen renal function as the result of systemic neurohormonal activation and direct renal vascular effects. UF also removes fluid, but its actions on intrarenal hemodynamics, and therefore renal function, are unknown.

METHODS

Patients hospitalized for acute decompensated heart failure with an ejection fraction less than 40% and two or more signs of hypervolemia were randomized to receive UF or intravenous diuretics. Urine output, GFR (as measured by iothalamate), and renal plasma flow (as measured by para-aminohippurate) were assessed before fluid removal and after 48 hours.

RESULTS

Nineteen patients (59 +/- 16 years, 68% were male) were randomized to receive UF (n = 9) or intravenous diuretics (n = 10). The change in GFR (-3.4 +/- 7.7 mL/min vs. -3.6 +/- 11.5 mL/min; P = .966), renal plasma flow (26.6 +/- 62.7 mL/min vs. 16.1 +/- 42.0 mL/min; P = .669), and filtration fraction (-6.9 +/- 13.6 mL/min vs. -3.9 +/- 13.6 mL/min; P = .644) after treatment were not significantly different between the UF and furosemide treatment groups, respectively. There was no significant difference in net 48-hour fluid removal between the groups (-3211 +/- 2345 mL for UF and -2725 +/- 2330 mL for furosemide, P = .682). UF removed 3666 +/- 2402 mL. Urine output during 48 hours was significantly greater in the furosemide group (5786 +/- 2587 mL) compared with the UF group (2286 +/- 915 mL, P < .001).

CONCLUSIONS

During a 48-hour period, UF did not cause any significant differences in renal hemodynamics compared with the standard treatment of intravenous diuretics.

Vasodilatation of afferent arterioles and paradoxical increase of renal vascular resistance by furosemide in mice

Loop diuretics like furosemide have been shown to cause renal vasodilatation in dogs and humans, an effect thought to result from both a direct vascular dilator effect and from inhibition of tubuloglomerular feedback. In isolated perfused afferent arterioles preconstricted with angiotensin II or N(G)-nitro-L-arginine methyl ester, furosemide caused a dose-dependent increase of vascular diameter, but it was without effect in vessels from NKCC1-/- mice suggesting that inhibition of NKCC1 mediates dilatation in afferent arterioles. In the intact kidney, however, furosemide (2 mg/kg iv) caused a 50.5 +/- 3% reduction of total renal blood flow (RBF) and a 27% reduction of superficial blood flow (SBF) accompanied by a marked and immediate increase of tubular pressure and volume. At 10 mg/kg, furosemide reduced RBF by 60.4 +/- 2%. Similarly, NKCC1-/- mice responded to furosemide with a 45.4% decrease of RBF and a 29% decrease of SBF. Decreases in RBF and SBF and increases of tubular pressure by furosemide were ameliorated by renal decapsulation. In addition, pretreatment with candesartan (2 mg/kg) or indomethacin (5 mg/kg) attenuated the reduction of RBF and peak urine flows caused by furosemide. Our data indicate that furosemide, despite its direct vasodilator potential in isolated afferent arterioles, causes a marked increase in flow resistance of the vascular bed of the intact mouse kidney. We suggest that generation of angiotensin II and/or a vasoconstrictor prostaglandin combined with compression of peritubular capillaries by the expanding tubular compartment are responsible for the reduction of RBF in vivo.

Role of nitric oxide pathway in hypotensive and renal effects of furosemide during extracellular volume expansion

OBJECTIVE

In previous studies we demonstrated that the administration of furosemide associated with L-arginine contributes to enhanced hypotension and induces greater water than electrolyte excretion, in both normal and expansion conditions. The aim of the present study was to elucidate the interaction between furosemide and the nitric oxide (NO) system in renal and vascular responses during extracellular volume expansion.

DESIGN AND METHODS

Expanded [10% body weight (bw)] and non-expanded anaesthetized male Wistar rats were treated with furosemide (7.5 mg/kg bw). Mean arterial pressure, nitrite and nitrate excretion (NOx) were determined. NADPH-diaphorase activity, a marker of nitric oxide synthase (NOS) activity, was measured histochemically in different segments of the nephron, aorta and renal arteries. NOS activity was determined using an L-[U14C]-arginine substrate in the kidney and aorta of expanded and non-expanded rats, in basal conditions and after furosemide (10 micromol/l).

RESULTS

The hypotensive effect of furosemide was enhanced when NO production was stimulated in expanded and non-expanded animals. The diuretic treatment induced a significant increase in NOx excretion, in NADPH-diaphorase activity in the thick ascending limb of Henle, renal arteries and aorta, and in NOS activity in aorta and kidney in both groups.

CONCLUSIONS

Our results suggest that the hypotensive effect of furosemide may be attributed to NO-mediated vasodilation. The enhanced NOS activity, observed in the renal artery of furosemide-treated rats, could explain the increased renal plasma flow induced by furosemide. In addition, NO-pathway stimulation in the kidney could be one of the mechanisms by which furosemide exerts its diuretic and natriuretic effects, in control and in expansion conditions.

Elevated non-esterified fatty acids impair nitric oxide independent vasodilation, in humans: evidence for a role of inwardly rectifying potassium channels

To evaluate the role of elevation of non-esterified fatty acids on forearm nitric oxide (NO) dependent and independent relaxation, four studies were performed in the forearms of 14 normals: (1). endothelium-dependent and -independent vasodilations were assessed during acetylcholine (Ach) and sodium nitroprusside (SNP) infusions; (2). flow-mediated vasodilation (FMD) was assessed; (3) .bradykinin (BK) was infused during NO and prostaglandin inhibition (NO clamp); (4). blood flow (FBF) was measured during Ouabain, a Na(+)/K(+) ATPase, and BaCl(2), rectifying potassium channel (K(IR)) blockers, respectively. All studies were performed before and after 120 min. Intralipid+heparin (high-NEFA) infusion. Ach-mediated FBF increase was lower at high-NEFA (332+/-34 vs. 436+/-44% at 45 microg l forearm(-1) min(-1); % of ratio infused: control arm P<0.05), while SNP response was similar. FMD did not differ before and during high-NEFA, which induced a blunted response of FBF during BK with or without NO clamp. Ouabain and BaCl(2)-mediated FBF inhibition was lower (P<0.01) at high-NEFA. During ouabain alone FBF decreased slightly.

IN CONCLUSION

High-NEFA exerts a negative role on both NO-dependent and independent vasodilations. The decrease in FBF, mediated by K(IR) inhibition, is blunted by high-NEFA: these substrates interfere with hemodynamic/metabolism coupling, possibly through the inhibition of these channels.

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.