Dilatory effect of furosemide on rat tracheal arterioles and venules

Sympathetic nerve-dependent regulation of mucosal vascular tone modifies airway smooth muscle reactivity

The airways contain a dense subepithelial microvascular plexus that is involved in the supply and clearance of substances to and from the airway wall. We set out to test the hypothesis that airway smooth muscle reactivity to bronchoconstricting agents may be dependent on airway mucosal blood flow. Immunohistochemical staining identified vasoconstrictor and vasodilator nerve fibers associated with subepithelial blood vessels in the guinea pig airways. Intravital microscopy of the tracheal mucosal microvasculature in anesthetized guinea pigs revealed that blockade of α-adrenergic receptors increased baseline arteriole diameter by ~40%, whereas the α-adrenergic receptor agonist phenylephrine produced a modest (5%) vasoconstriction in excess of the baseline tone. In subsequent in vivo experiments, tracheal contractions evoked by topically applied histamine were significantly reduced (P < 0.05) and enhanced by α-adrenergic receptor blockade and activation, respectively. α-Adrenergic ligands produced similar significant (P < 0.05) effects on airway smooth muscle contractions evoked by topically administered capsaicin, intravenously administered neurokinin A, inhaled histamine, and topically administered antigen in sensitized animals. These responses were independent of any direct effect of α-adrenergic ligands on the airway smooth muscle tone. The data suggest that changes in blood flow in the vessels supplying the airways regulate the reactivity of the underlying airway smooth muscle to locally released and exogenously administered agents by regulating their clearance. We speculate that changes in mucosal vascular function or changes in neuronal regulation of the airway vasculature may contribute to airways responsiveness in disease.

Furosemide inhalation in dyspnea of mustard gas-exposed patients: a triple-blind randomized study

Dyspnea is the hallmark symptom of some respiratory diseases such as chronic obstructive pulmonary disease and bronchiolitis and is a major reason for which these patients seek medical attention. We performed a randomized triple-blind controlled crossover clinical trial in which we compared the efficacy of inhaled furosemide (4 ml equal to 40 mg in 10 min) with placebo (4 ml of 0.9% saline solution) in 41 mustard gas-exposed patients. Dyspnea index, visual analog scale (VAS), and pulmonary function test results were obtained before and 4 h after treatments. Results showed that both furosemide and placebo significantly decreased VAS and dyspnea index and increased FEV(1), FVC, and FEV(1)/FVC, while there was no difference between the two drugs in these effects (p values .23, .61, .81, .36, and .27, respectively). Our results failed to address the previously reported effects of inhaled furosemide on dyspnea. In fact, we suggest that patients with a previous exposure to sulfur mustard, in which chronic bronchitis and bronchiolitis are the most suggested underlying mechanisms, may not benefit from furosemide to alleviate their dyspnea.

Immunolocalization of a Na-K-2Cl cotransporter in human tracheobronchial smooth muscle

Inhibition of the Na-K-2Cl (NKCC) cotransporter by loop diuretics is associated with airway relaxation, but there has been no direct evidence for the expression of this protein in airway smooth muscle. Thus we hypothesized that a NKCC cotransporter is present and functional in airway smooth muscle cells. Monoclonal and polyclonal antibodies were used first to demonstrate the presence of a NKCC cotransporter protein in isolated human fetal trachea and normal human bronchial smooth muscle cells (BSMC) by Western blotting. The cotransporter protein was then localized by immunohistochemical staining to airway smooth muscle cells in culture and in situ. The localization was confirmed by indirect immunofluorescence and laser confocal microscopy in the BSMC. Cotransporter function in BSMC was also confirmed in vitro by bumetanide-mediated inhibition of rubidium uptake. Our present findings thus document the presence of a functional NKCC cotransporter in human airway smooth muscle, providing a basis for defining the role of this ion cotransporter in airway smooth muscle function.

Loop diuretics and in vitro relaxation of human fetal and newborn mouse airways

This study was designed to test the hypotheses that furosemide directly causes relaxation in human fetal airway and that delivery of loop diuretics to either the adventitial or epithelial surface of newborn mouse airway results in equivalent relaxation. Isometric tension changes were measured in human fetal (11-16 wk) trachea and mainstem bronchus rings exposed to furosemide (300 microM) or saline after acetylcholine or leukotriene D(4) constriction. Significant decreases in isometric tension to furosemide were demonstrated after constriction with acetylcholine or leukotriene D(4). To examine the site of effect and mimic aerosolized and systemic administration, furosemide (3-300 microM) and bumetanide (0.3-30 microM) were applied separately to epithelial and adventitial surfaces of newborn mouse airways. No differences in airway diameter changes to epithelial or adventitial furosemide or bumetanide were observed, but a 10-fold difference in potency was found. In summary, human fetal airway relaxed to furosemide when constricted with either neurotransmitter or inflammatory mediator in vitro. Further, no differences in relaxation to equimolar epithelial and adventitial furosemide were observed in isolated newborn mouse airway. Taken together, this provides evidence that furosemide has a direct, nonepithelial-dependent effect on airway smooth muscle tone.

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

1. Relaxing effect of loop diuretics, piretanide and furosemide in comparison with acetylcholine (ACh) was investigated in guinea-pig isolated mesenteric resistance arteries. 2. Concentration-response curves to ACh (0.001 - 10 microM) and diuretics (0.0001 - 1 microM) were constructed in noradrenaline (10 - 30 microM)-precontracted arteries incubated either in normal physiological salt solution (PSS) or in 30 mM KCl PSS (K-PSS). 3. In PSS, maximal relaxations (R(max)) and pD(2) to ACh were 87+/-2% and 7.1+/-0.1 (n=10). L-N(G)-nitro-arginine methyl ester (L-NAME, 100 microM) reduced R(max) by 20% (P<0.01, n=7) and pD(2) by 10% (P<0.01). In contrast, indomethacin (10 microM) increased R(max) by 19% (P<0.01, n=8) and pD(2) by 10% (P<0.05). Combination of L-NAME+indomethacin reversed the effect observed with either of these inhibitors used alone. In K-PSS, R(max) was attenuated by 40% (P<0.001, n=6) compared to PSS. L-NAME reduced R(max) by 65% (P<0.01, n=5) and increased pD(2) by 15 fold. L-NAME+indomethacin suppressed the resistant relaxation. 4. In PSS+L-NAME+indomethacin, inhibitors of small (SK(Ca); apamin, 0.1 microM) and large (BK(Ca); iberiotoxin and charybdotoxin, 0.1 microM) conductance Ca(2+)-sensitive K(-)-channels used alone had little effect on the ACh-response. Combination of apamin+iberiotoxin reduced R(max) by 40% (P<0.05, n=7) while apamin+charybdotoxin fully abolished the resistant relaxation. 5. In PSS, piretanide and furosemide induced relaxation with R(max): 89+/-3% vs 84+/-5% and pD(2): 8.5+/-0.1 vs 7.7+/-0.2 (P<0.01) for piretanide (n=11) and furosemide (n=10), respectively. Endothelial abrasion suppressed relaxation to diuretics. L-NAME and indomethacin used alone or in combination did not significantly modify the response to diuretics. 6. In K-PSS, piretanide-induced relaxation was abolished whereas that to furosemide was reduced by 70% (P<0.001, n=9) compared to PSS and was suppressed by L-NAME+indomethacin. In PSS+L-NAME+indomethacin, apamin slightly reduced relaxation to diuretics whereas charybdotoxin or iberiotoxin abolished the response. 7. These results indicate that ACh-evoked relaxation is mediated by both NO/PGl(2)-dependent and -independent mechanisms. The EDHF-dependent component relies on activation of Ca(2+)-activated K(+) channels, is sensitive to a combination of apamin+charybdotoxin and to a smaller degree to a combination of apamin+iberiotoxin. Loop diuretic-induced relaxation is endothelium-dependent, appears to be mediated by NO, PGl(2) and EDHF for furosemide and EDHF only for piretanide. For the two diuretics, opening of BK(Ca) channels may be involved in the relaxation.

Differential effects of furosemide on porcine bronchial arterial and airway smooth muscle

Furosemide attenuates airway obstruction in asthmatic subjects when administered as an aerosol pretreatment. This protective effect of furosemide could be related to relaxation of bronchial smooth muscle or to increased bronchial blood flow. To determine whether furosemide dilates bronchial smooth muscle, isometric contractile responses in distal bronchi from young pigs were studied. In bronchial smooth muscle rings that were precontracted with 10(-5) M acetylcholine, significant relaxation occurred with 10(-8) to 3 x 10(-6) M isoproterenol but not with 10(-8) to 10(-3) M furosemide. In contrast, bronchial arteries that were precontracted with either 10(-4) M norepinephrine or 10(-8) M vasopressin significantly relaxed in response to 10(-4) to 3 x 10(-3) M and 10(-3) to 3 x 10(-3) M furosemide, respectively. We conclude that furosemide, under the described experimental conditions, relaxes airway vascular smooth muscle but not bronchial smooth muscle. These results are consistent with previous suggestions that inhaled furosemide increases blood flow to airway tissues (Gilbert IA, Lenner KA, Nelson JA, Wolin AD, and Fouke JM. J Appl Physiol 76: 409-415, 1994).

Furosemide inhibits thromboxane A2-induced contraction in isolated human internal mammary artery and saphenous vein

Evidence suggests that, in addition to its diuretic property, furosemide also may exert direct vascular effects. Because thromboxane A2 (TXA2) has a role in the control of vascular tone, we investigated the effect of furosemide on the contraction induced by U46619 (a stable TXA2 mimetic) on isolated human internal mammary artery (IMA) and saphenous vein (SV). Concentration-response curves to U46619 were performed in the absence (vehicle) or the presence of furosemide (0.1-1 mM) on rings of IMA and SV. In addition, the relaxant effect of furosemide (0.1 microM-1 mM) also was evaluated on U46619-precontracted IMA and SV. The participation of cyclooxygenase derivatives was studied by pretreatment with indomethacin. Furosemide (0.1-1.0 mM) caused parallel rightward shifts of U46619 concentration-response curves without affecting the maximal responses in both IMA and SV. Treatment with indomethacin (1 microM) modified neither the inhibitory effect of furosemide on U46619-induced contractions, nor the relaxant effect of furosemide on U46619-induced contractions, nor the relaxant effect of furosemide on U46619-precontracted IMA and SV. In conclusion, furosemide at high concentrations inhibited U46619-induced contraction in human isolated IMA and SV and relaxed U46619-precontracted IMA and SV by mechanisms independent of the release of relaxant prostaglandins. These results suggest that blockade of TXA2 receptors by furosemide may contribute to explaining the therapeutic effects of furosemide in the treatment of severe heart failure.

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.