Qualitative and quantitative DECT pulmonary angiography in COVID-19 pneumonia and pulmonary embolism.

AIM: To assess differences in qualitative and quantitative parameters of pulmonary perfusion from dual-energy computed tomography (CT) pulmonary angiography (DECT-PA) in patients with COVID-19 pneumonia with and without pulmonary embolism (PE). MATERIALS AND METHODS: This retrospective institutional review board-approved study included 74 patients (mean age 61±18 years, male:female 34:40) with COVID-19 pneumonia in two countries (one with 68 patients, and the other with six patients) who underwent DECT-PA on either dual-source (DS) or single-source (SS) multidetector CT machines. Images from DS-DECT-PA were processed to obtain virtual mono-energetic 40 keV (Mono40), material decomposition iodine (MDI) images and quantitative perfusion statistics (QPS). Two thoracic radiologists determined CT severity scores based on type and extent of pulmonary opacities, assessed presence of PE, and pulmonary parenchymal perfusion on MDI images. The QPS were calculated from the CT Lung Isolation prototype (Siemens). The correlated clinical outcomes included duration of hospital stay, intubation, SpO2 and death. The significance of association was determined by receiver operating characteristics and analysis of variance. RESULTS: One-fifth (20.2%, 15/74 patients) had pulmonary arterial filling defects; most filling defects were occlusive (28/44) located in the segmental and sub-segmental arteries. The parenchymal opacities were more extensive and denser (CT severity score 24±4) in patients with arterial filling defects than without filling defects (20±8; p=0.028). Ground-glass opacities demonstrated increased iodine distribution; mixed and consolidative opacities had reduced iodine on DS-DECT-PA but increased or heterogeneous iodine content on SS-DECT-PA. QPS were significantly lower in patients with low SpO2 (p=0.003), intubation (p=0.006), and pulmonary arterial filling defects (p=0.007). CONCLUSION: DECT-PA QPS correlated with clinical outcomes in COVID-19 patients.

Ischaemic stroke prevention in patients with atrial fibrillation and high bleeding risk: opportunities and challenges for percutaneous left atrial appendage occlusion.

Patients with atrial fibrillation (AF) are at an increased risk of ischaemic stroke. The efficacy of stroke prevention with vitamin K antagonists in these patients has been well established. However, associated bleeding risks may offset the therapeutic benefits in patients with risk factors for bleeding. Despite improvements achieved by novel oral anticoagulants, bleeding remains a clinically relevant problem, especially gastrointestinal bleeding. Percutaneous occlusion of the left atrial appendage (LAA) may be considered as an alternative stroke prevention therapy in AF patients with a high bleeding risk. This paper explores patient groups in whom oral anticoagulation may be challenging and percutaneous LAA occlusion (LAAO) has a potentially better risk-benefit balance. The current status of LAAO and future directions are reviewed, and particular challenges for LAA occlusion requiring further clinical data are discussed. This article is a summary of the Third Global Summit on LAA occlusion, 15 March 2013, Barcelona, Spain.

Effects of mechanical ventilation versus apnea on bi-ventricular pressure-volume loop recording.

Respiration changes intrathoracic pressure and lung volumes in a cyclic manner, which affect cardiac function. Invasive ventricular pressure-volume (PV) loops can be recorded during ongoing mechanical ventilation or in transient apnea. No consensus exists considering ventilatory mode during PV loop recording. The objective of this study was to investigate the magnitude of any systematic difference of bi-ventricular PV loop variables recorded during mechanical ventilation versus apnea. PV loops were recorded simultaneously from the right ventricle and left ventricle in a closed chest porcine model during mechanical ventilation and in transient apnea (n=72). Variables were compared by regression analyses. Mechanical ventilation versus apnea affected regression coefficients for important PV variables including right ventricular stroke volume (1.22, 95% CI [1.08-1.36], p=0.003), right ventricular ejection fraction (0.90, 95% CI [0.81-1.00], p=0.043) and right ventricular arterial elastance (0.61, 95%CI [0.55-0.68], p<0.0001). Right ventricular pressures and volumes were parallelly shifted with Y-intercepts different from 0. Few left ventricular variables were affected, mainly first derivatives of pressure (dP/dt(max): 0.96, 95% CI [0.92-0.99], p=0.016, and dP/dt(min): 0.92, 95% CI [0.86-0.99], p=0.026), which might be due to decreased heart rate in apnea (Y-intercept -6.88, 95% CI [-12.22; -1.54], p=0.012). We conclude, that right ventricular stroke volume, ejection fraction and arterial elastance were mostly affected by apnea compared to mechanical ventilation. The results motivate future standardization of respiratory modality when measuring PV relationships.

Comparison of two sulfonylureas with high and low myocardial K(ATP) channel affinity on myocardial infarct size and metabolism in a rat model of type 2 diabetes.

AIMS/HYPOTHESIS: Sulfonylureas (SUs) may impair outcome in patients with acute coronary syndrome. Most experimental studies of the myocardial effects of SU treatment are performed in non-diabetic models. We compared the effect of two widely used SUs, glibenclamide (gb) and gliclazide (gc), with high and low myocardial K(ATP) channel affinity, respectively, at therapeutic concentrations on infarct size, left ventricular (LV) function and myocardial glycogen, lactate and alanine content before and after ischaemia/reperfusion (I/R). METHODS: Non-diabetic Wistar and diabetic Goto-Kakizaki rat hearts were investigated in a Langendorff preparation. Gb (0.1 µmol/l) and gc (1.0 µmol/l) were administrated throughout the study. Infarct size was evaluated after 120 min of reperfusion. Myocardial metabolite content was measured before and after ischaemia. RESULTS: Infarct size was smaller in diabetic hearts than in non-diabetic hearts (0.33 ± 0.03 vs 0.51 ± 0.05, p < 0.05). Gb increased infarct size (0.54 ± 0.04 vs 0.33 ± 0.03, p < 0.05) and reduced post-ischaemic LV developed pressure (60 ± 3 vs 76 ± 3 mmHg, p < 0.05) and coronary flow (4.9 ± 0.5 vs 7.1 ± 0.4 ml min(-1) g(-1), p < 0.05) in gb-treated diabetic rats compared with untreated diabetic rats. On comparing gb-treated diabetic rats with untreated diabetic rats, glycogen content was reduced before (9.1 ± 0.6 vs 13.6 ± 1.0 nmol/mg wet weight, p < 0.01) and after ischaemia (0.9 ± 0.2 vs 1.8 ± 0.2 nmol/mg wet weight, p < 0.05), and lactate (4.8 ± 0.4 vs 3.2 ± 0.3 nmol/mg wet weight, p < 0.01) and alanine (1.38 ± 0.12 vs 0.96 ± 0.09 nmol/mg wet weight, p < 0.05) contents were increased during reperfusion. Gc-treatment of diabetic and non-diabetic rats did not affect any of the measured variables. CONCLUSIONS/INTERPRETATIONS: Gb, but not gc, exacerbates I/R injury and deteriorates LV function in diabetic hearts. These effects of gb on diabetic hearts may be due to detrimental effects on myocardial carbohydrate metabolism.

Nitroglycerin-mediated vasorelaxation is modulated by endothelial calcium-activated potassium channels.

OBJECTIVE: Recent in vitro data suggest, large conductance calcium-activated K+ channels (BKCa) modulate the vascular response to nitric oxide (NO). The in vivo implications and the characteristics of this interaction are not clear. This study firstly investigates whether modulation of BKCa affects the vascular response to nitroglycerin (NTG)-derived NO in vivo and in the isolated heart and secondly examines the influence of endothelial BKCa on NTG-mediated vasodilation in vitro. METHODS: The hypotensive effect of NTG was measured in conscious, chronically catheterized rats during i.v. infusions of iberiotoxin (IbTX, a selective inhibitor of BKCa) or placebo. Similarly, NTG-induced flow-changes in the isolated perfused rat heart were examined before and after IbTX treatment (0.1 microM). Concentration-relaxation curves to NTG in the presence of various K+ channel modulating agents were performed in vitro on porcine coronary arteries with and without intact endothelium. RESULTS: I.v. infusion of IbTX reduced the in vivo hypotensive effect of NTG by 55% (before IbTX: 32.0 +/- 3.0 mmHg, vs. after IbTX: 14.5 +/- 3.2 mmHg, P < 0.05) and nearly abolished NTG-induced increase in coronary flow in the isolated perfused heart (P < 0.05). In vitro, this effect depended on an intact endothelium (endothelium intact segments; NTG: pD2 = 5.8 +/- 0.1, Emax = 97.6 +/- 3.2% vs. NTG + IbTX: pD2 = 4.9 +/- 0.2, Emax = 49.7 +/- 6.2%, P < 0.05; endothelium denuded segments; NTG: pD2 = 6.9 +/- 0.1, Emax = 104.0 +/- 1.4% vs. NTG + IbTX: pD2 = 6.7 +/- 0.1, Emax = 100 +/- 1.2%, P > 0.05). CONCLUSION: The results suggest, that modulation of endothelial BKCa significantly affects NTG-induced vasorelaxation in vitro, in the isolated perfused heart and in vivo.

Atrial fibrillation and stroke in adult patients with atrial septal defect and the long-term effect of closure.

OBJECTIVE: To estimate the risk of atrial fibrillation (AF) and stroke and the impact of closure in patients with atrial septal defect (ASD) compared with a general population cohort. METHODS: All adult Danish patients (>18 years) diagnosed with ASD from 1977 to 2009 (N=1168) were identified through population-based registries. Using Cox regression, we compared ASD patients' risk of AF and stroke with an age-matched and gender-matched comparison cohort. We computed prevalence proportions of anticoagulation and antiarrhythmic medicine use before and after closure and described stroke-related mortality. RESULTS: Median follow-up was 9.6 years (range 1-33 years). Patients with ASD had a higher risk of first-time AF (adjusted HR 8.2; 95% CI 6.6 to 10.2) after closure than the comparison cohort, but with no difference between transcatheter and surgical closure (HR 1.5, 95% CI 0.6 to 3.5). Patients without prevalent AF had a 10-year cumulative incidence of AF of 11% (95% CI 9% to 14%) after closure compared with 2% (95% CI 1.8% to 2.5%) in the comparison cohort. Patients with ASD with prevalent AF continued to use anticoagulation medicine after closure/diagnosis. Patients with ASD had increased risk of stroke without closure (adjusted HR 2.6; 95% CI 1.4 to 3.0) and with closure (adjusted HR 2.0; 95% CI 1.4 to 2.7). Risk of stroke after closure was related to AF (HR adjusted for AF 1.3; 95% CI 0.9 to 1.9). CONCLUSIONS: Patients with ASD had a higher risk of first-time AF after closure than the comparison cohort. There was no effect of closure on the use of AF-related medicine in patients with prevalent AF.

Effects of verapamil on diurnal and thyrotropin-releasing hormone-stimulated prolactin levels in man.

The effects of the calcium entry blocker verapamil on the 24-h profile of PRL secretion and on the PRL response to TRH were investigated in six healthy volunteers. Verapamil (120 mg, three times daily) was administered orally for 1 week. In all subjects both basal and TRH-stimulated PRL levels were markedly elevated by verapamil. The average diurnal PRL concentration was increased from 13.0 +/- 2.0 micrograms/L to 25.2 +/- 4.4 (mean +/- SE; P = 0.02). Diurnal rhythm and pulsatility of PRL secretion were seen both before and during verapamil administration. Mean peak PRL concentrations after TRH injection (200 micrograms, iv) were significantly increased from 72.6 +/- 11.6 to 115.2 +/- 16.8 (P less than 0.01), and the mean area under the PRL concentration-time curves from 4332 +/- 962 micrograms/L.120 min to 6975 +/- 1334 (P = 0.01). The data are in striking contrast with previous findings from in vitro studies where verapamil has been reported to block calcium-mediated stimulus-secretion coupling and inhibit hormone secretion from pituitary cells. Interference with other PRL-regulating mechanisms may account for the demonstrated verapamil-induced PRL secretion in vivo.

Characterization of NS 2028 as a specific inhibitor of soluble guanylyl cyclase.

1 The haeme-containing soluble guanylyl cyclase (alpha1beta1-heterodimer) is a major intracellular receptor and effector for nitric oxide (NO) and carbon monoxide (CO) and mediates many of their biological actions by increasing cyclic GMP. We have synthesized new oxadiazolo-benz-oxazins and have assessed their inhibitory actions on guanylyl cyclase activity in vitro, on the formation of cyclic GMP in cultured cells and on the NO-dependent relaxation of vascular and non-vascular smooth muscle. 2 Soluble guanylyl cyclase, purified to homogeneity from bovine lung, was inhibited by 4H-8-bromo-1,2,4-oxadiazolo(3,4-d)benz(b)(1,4)oxazin-1-one (NS 2028) in a concentration-dependent and irreversible manner (IC50 30 nM for basal and 200 nM for NO-stimulated enzyme activity). Evaluation of the inhibition kinetics according to Kitz & Wilson yielded a value of 8 nM for Ki, the equilibrium constant describing the initial reversible reaction between inhibitor and enzyme, and 0.2 min(-1) for the rate constant k3 of the subsequent irreversible inhibition. Inhibition was accompanied by a shift in the soret absorption maximum of the enzyme's haem cofactor from 430 to 390 nm. 3 S-nitroso-glutathione-enhanced soluble guanylyl cyclase activity in homogenates of mouse cerebellum was inhibited by NS 2028 (IC50 17 nM) and by 17 structural analogues in a similar manner, albeit with different potency, depending on the type of substitution at positions 1, 7 and 8 of the benzoxazin structure. Small electronegative ligands such as Br and Cl at position 7 or 8 increased and substitution of the oxygen at position 1 by -S-,- NH- or -CH2- decreased the inhibition. 4 In tissue slices prepared from mouse cerebellum, neuronal NO synthase-dependent activation of soluble guanylyl cyclase by the glutamate receptor agonist N-methyl-D-aspartate was inhibited by NS 2028 (IC50 20 nM) and by two of its analogues. Similarly, 3-morpholino-sydnonimine (SIN-1)-elicited formation of cyclic GMP in human cultured umbilical vein endothelial cells was inhibited by NS 2028 (IC50 30 nM). 5 In prostaglandin F2alpha-constricted, endothelium-intact porcine coronary arteries NS 2028 elicited a concentration-dependent increase (65%) in contractile tone (EC50 170 nM), which was abolished by removal of the endothelium. NS 2028 (1 microM) suppressed the relaxant response to nitroglycerin from 88.3+/-2.1 to 26.8+/-6.4% and induced a 9 fold rightward shift (EC50 15 microM) of the concentration-relaxation response curve to nitroglycerin. It abolished the relaxation to sodium nitroprusside (1 microM), but did not affect the vasorelaxation to the KATP channel opener cromakalim. Approximately 50% of the relaxant response to sodium nitroprusside was recovered after 2 h washout of NS 2028. 6 In phenylephrine-preconstricted, endothelium-denuded aorta of the rabbit NS 2028 (1 microM) did not affect relaxant responses to atrial natriuretic factor, an activator of particulate guanylyl cyclase, or forskolin, an activator of adenylyl cyclase. 7 NO-dependent relaxant responses in non-vascular smooth muscle were also inhibited by NS 2028. The nitroglycerin-induced relaxation of guinea-pig trachea preconstricted by histamine was fully inhibited by NS 2028 (1 microM), whereas the relaxations to terbutaline, theophylline and vasoactive intestinal polypeptide (VIP) were not affected. The relaxant responses to electrical field stimulation of non-adrenergic, non-cholinergic nerves in the same tissue were attenuated by 50% in the presence of NS 2028 (1 microM). 8 NS 2028 and its analogues, one of which is the previously characterized 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ), appear to be potent and specific inhibitors of soluble guanylyl cyclase present in various cell types. Oxidation and/or a change in the coordination of the haeme-iron of guanylyl cyclase is a likely inhibitory mechanism.

Lack of effect of the vasodilator pinacidil on insulin secretion in healthy humans.

Pinacidil is a new antihypertensive vasodilator drug which is supposed to act by opening of ATP-sensitive and glibenclamide-sensitive K+ channels in vascular smooth muscle cell membranes. Similar K+ channels play an important role in insulin secretion from pancreatic islets cells. Inhibition of insulin secretion has been demonstrated with high concentrations of pinacidil in vitro. In the present study the insulin response to oral glucose were studied in six healthy subjects before and on the last day of 2 weeks treatment with pinacidil. The drug was given by the oral route 12.5 mg bid in the first week and 25 mg bid in the second. There were no significant changes in fasting blood levels of insulin or glucose, glucose-stimulated insulin secretion, or oral glucose tolerance during pinacidil administration. These results may suggest that pinacidil at therapeutic concentrations does not activate insulin regulating K+ channels in pancreatic islet cells.

Glibenclamide inhibits hypoxic relaxation of isolated porcine coronary arteries under conditions of impaired glycolysis.

The possible involvement of ATP-sensitive K+ channels (KATP) in hypoxic relaxation of isolated porcine coronary arteries was investigated. Tubular segments taken from the left anterior descending artery were suspended in myographs for recording of isometric contractile force. Hypoxia (pO2 = 20.3 mm Hg +/- 0.5) produced a greater relaxation in preparations contracted by 30 mM K+ (49.7% +/- 7.2) compared with 124 mM K+ (19.9% +/- 2.2) which is compatible with the involvement of K+ channel activation in the mechanism of hypoxic relaxation. In a normal glucose-containing Krebs solution the KATP blocker glibenclamide (1 microM) failed to influence the hypoxic relaxation of preparations contracted by the thromboxane A2 analogue U-46619. Under conditions created to inhibit non-oxidative ATP production from glycolysis using a glucose-free Krebs solution containing 2-deoxyglucose (10 mM), the hypoxic relaxation was enhanced from 54.5% +/- 5.0 to 77.2% +/- 4.4. Under these conditions glibenclamide (1 microM) significantly inhibited the hypoxic relaxant response from 77.2% +/- 4.2 to 55.2% +/- 4.4 and prolonged the time until half-maximal relaxation from 5.5 min +/- 0.6 to 8.1 min +/- 0.6. A low concentration of the KATP opener levcromakalim (30 nM) failed to significantly potentiate the hypoxic relaxation. The adenosine receptor blocker theophylline (1 microM) or removal of the endothelium showed no effect on the hypoxic relaxation. In normal glucose-containing Krebs solution, indomethacin (10 microM) caused a small but significant inhibition of the hypoxic relaxation from 54.5% +/- 5.0 to 41.6% +/- 3.6.(ABSTRACT TRUNCATED AT 250 WORDS)

Antidiabetic sulfonylureas relax isolated rabbit coronary arteries.

Antidiabetic sulfonylureas completely relaxed isolated rabbit coronary arteries contracted by prostaglandin F2 alpha. The order of potency was glibenclamide (EC50 = 4.75 microM) greater than glipizide = glibornuride = tolbutamide = chlorpropamide. The drugs also relaxed the contractions induced by 30 mM K+ but much less potently. The effectiveness of the drugs as vascular smooth muscle relaxants did not correlate with their ability to antagonize the vasorelaxant action of cromakalim. Sulfonylurea-induced vasorelaxation probably involves mechanisms other than an interaction with ATP-regulated K+ channels.

Effects of pinacidil and other cyanoguanidine derivatives on guinea-pig isolated trachea, aorta and pulmonary artery.

The effects of pinacidil and four other cyanoguanidine derivatives (P 1060, P 1106, P 1787, P 1890) were evaluated on guinea-pig isolated trachea, aorta and pulmonary artery. All compounds were effective smooth muscle relaxants. Concentration-relaxation curves and corresponding EC50 and Emax values were determined in preparations contracted by histamine, prostaglandin F2 alpha, 30 mM K+ or 124 mM K+. Pinacidil relaxed trachea by 100% and vascular tissues by 70%. P 1060 and P 1106 also produced complete tracheal relaxation, but had a lower maximal effect of 40% in vascular smooth muscle. P 1787 and P 1890 relaxed all three types of tissues by 100%. The order of potency of the drugs was P 1106 greater than P 1060 greater than pinacidil greater than P 1890 greater than P 1787. Pinacidil, P 1060 and P 1106 were more potent on pulmonary artery than on aortic preparations. Based on the effects of the drugs on 30 mM K(+)- and 124 mM K(+)-induced contractions and the ability of glibenclamide to antagonize the drugs, P 1060 and P 1106 appeared to be pure K+ channel openers whereas pinacidil seemed to operate by additional mechanisms. P 1787 and P 1890 relaxed smooth muscle by a mechanism other than opening of K+ channels.

Effects of levcromakalim and glibenclamide on paced guinea-pig atrial strips exposed to hypoxia.

Isolated strips of guinea-pig atrial myocardium were mounted in isometric myographs and electrically paced for measurements of myocardial contractile function. Levcromakalim, a K+ channel opener, completely inhibited the contractile force in a concentration-dependent way (EC50 = 15 microM). Glibenclamide (3 microM), a blocker of ATP-regulated K+ channels (KATP), caused a 5-fold rightward shift of the concentration-effect curve. Exposure of the atrial strips to hypoxia caused a time-dependent loss of contractility from 100% to a minimum level of 60% within 12 min. Levcromakalim (1 microM, 3 microM and 10 microM) concentration-dependently enhanced the hypoxia-induced inhibition of contractile function whereas levcromakalim (0.01 microM and 0.1 microM) had no significant effect. In the presence of levcromakalim (10 microM) hypoxia reduced the contractile force to 25%. Glibenclamide (3 microM) totally antagonized the enhancing effect of levcromakalim. When hypoxia was induced in glucose-free Krebs solution with 2-deoxyglucose, the myocardial contractility was completely suppressed within 12 min. Glibenclamide by itself (3 microM) failed to influence the myocardial response to hypoxia both in normal Krebs solution and under conditions of impaired glycolysis. The results indicate that levcromakalim by activation of myocardial ATP-regulated K+ channels accelerates and enhances the hypoxia-induced inhibition of myocardial contractile function. This effect may possibly contribute to the mechanism by which K+ channel openers exert cardioprotection. The results further suggest that mechanisms different from activation of KATP take a major part in the depressant mechanical response to hypoxia and glycolytic blockade in the guinea-pig atrial myocardium.

Effects of K+ channel blockers on the relaxant action of dihydralazine, cromakalim and nitroprusside in isolated rabbit femoral arteries.

The relaxant responses to dihydralazine and the influence of different K+ channel blockers were studied in isolated rabbit femoral arteries. The prototype K+ channel opener, cromakalim, and nitroprusside, which does not produce relaxation by K+ channel activation were used for comparison. Dihydralazine was most effective on contractions induced by noradrenaline (EC50 = 1.1 microM; Emax = 95%) and relaxed the contractions elicited by 20 mM K+ (EC50 = 2.0 microM; Emax = 81% in preference to 124 mM K(+)-induced contractions (EC50 = 30.1 microM; Emax = 54%). Cromakalim, but not nitroprusside, also selectively relaxed 20 mM K(+)-induced contractions. In noradrenaline-contracted arteries, glibenclamide (10 microM) completely suppressed the relaxant response to cromakalim but did not influence the vasorelaxation produced by dihydralazine or nitroprusside. Tetraethylammonium (8 mM) and Cs+ (4 mM) shifted the concentration-relaxation curve for dihydralazine 2-fold to the right, whereas Ba2+ (0.1 mM), 4-aminopyridine (5 mM) and procaine (0.1 mM) failed to influence dihydralazine-induced responses. Tetraethylammonium (8 mM) shifted the concentration-relaxation curve for cromakalim and nitroprusside 6-fold to the right and suppressed the maximal relaxant effects by about 30%. It is concluded that dihydralazine produces vascular smooth muscle relaxation by a mechanism different from the opening of glibenclamide- and ATP-sensitive K+ channels.

Smooth muscle relaxation and inhibition of responses to pinacidil and cromakalim induced by phentolamine in guinea-pig isolated trachea.

A concentration-dependent relaxant effect of phentolamine was demonstrated in guinea-pig isolated trachea and was probably unrelated to its alpha-adrenoceptor blocking action. The maximal effect of phentolamine against spontaneous tracheal tone was in the 24-100% range. However, phentolamine produced 100% relaxation when the tone was induced by histamine, carbachol, 30 mM K+ or 124 mM K+. Relaxant EC50 values ranged from 8 to 50 microM with the highest potency found against histamine-induced contractions. Phentolamine caused no suppression of contractions elicited by prostaglandin F2 alpha (PGF2 alpha) or leukotriene C4 (LTC4). At a concentration of 100 microM the alpha 2-adrenoceptor blocker, yohimbine, produced minor inhibition of spasmogen-induced tone, whereas the alpha 1-adrenoceptor blocker prazosin (up to 10 microM) had no inhibitory effects in the trachealis. Propranolol (1 microM), prazosin (1 microM), yohimbine (100 microM), tetrodotoxin (3 microM), glibenclamide (10 microM), tetraethylammonium (8 mM), 4-aminopyridine (5 mM), procaine (100 microM), dipyridamole (3 microM) or methylene blue (100 microM) did not influence the relaxant responses to phentolamine. In tracheal preparations contracted by PGF2 alpha or LTC4, phentolamine (1, 10 and 100 microM) antagonized the relaxant action of the K+ channel openers, pinacidil and cromakalim. The concentration-relaxation curves for pinacidil were shifted 30-fold to the right without change in the maximal effects, whereas the maximal cromakalim-induced relaxant responses were markedly suppressed by phentolamine.

Involvement of K+ channels in the relaxant effect of vasoactive intestinal peptide and atrial natriuretic peptide in isolated guinea-pig trachea.

The possible contribution of K+ channel activation to airway smooth muscle relaxation induced by vasoactive intestinal peptide (VIP) and atrial natriuretic peptide (ANP) was investigated in isolated guinea-pig trachea. Concentration-relaxation (CR) curves were assessed in preparations precontracted by 30 mM K+, 124 mM K+ or histamine either alone or in the presence of a K+ channel blocker: iberiotoxin (IbTX), glipizide, tetraethylammonium (TEA) or Ba2+. VIP completely relaxed contractions induced by histamine but had a lower effectiveness against those induced by 30 mM K+ and 124 mM K+. IbTX and TEA shifted the CR curve for VIP 5 and 14 times to the right, respectively. Glipizide and Ba2+ did not significantly antagonize the action of VIP. ANP relaxed contractions induced by histamine and 30 mM K+ but failed to relax those elicited by 124 mM K+. IbTX and TEA shifted the CR curve for ANP 8 and 46 times to the right, respectively. Glipizide and Ba2+ suppressed the maximal effect produced by ANP, and glipizide also shifted the CR curve to the left. The K+ channel opener levcromakalim relaxed tracheal contractions induced by histamine and 30 mM K+ but not those induced by 124 mM K+. Glipizide caused a 5-fold rightward shift of the CR curve for levcromakalim whereas IbTX shifted the curve to the left and increased the maximal relaxant effect. The Ca2+ channel blocker isradipine completely relaxed contractions induced by 30 mM K+ and 124 mM K+ but only partially relaxed those contracted by histamine. All four K+ channel blockers increased the maximal relaxant effect and shifted the CR curve for isradipine to the left. The results suggest that airway smooth muscle relaxation produced by VIP and ANP involves activation of large-conductance Ca(2+)-activated K+ channels (BKCa) and further that ANP may possibly activate other types of K+ channels additional to BKCa.

Effects of pinacidil on guinea-pig airway smooth muscle contracted by asthma mediators.

Pinacidil is a new antihypertensive, direct vasodilator drug which has been classified as a K+ channel opener. The present study demonstrated a concentration-dependent relaxant activity of pinacidil in guinea-pig tracheal preparations. The potency and efficacy of pinacidil depended on the agent used to induce tracheal tone. Tracheal preparations with spontaneous tone or precontracted by different asthma mediators were completely relaxed by pinacidil. A high potency was found in spontaneously contracted preparations (EC50 = 7.8 x 10(-7) M). The EC50 values ranged from 2.3 to 5.4 x 10(-6) M in histamine-, PGF2 alpha- or LTC4-contracted preparations. When tone was induced by carbachol, the EC50 was 2.1 x 10(-5) M. In contrast, pinacidil produced incomplete relaxation and had a low potency in preparations contracted by 30 or 124 mM K+ Krebs solutions. This effect profile differed from that seen with beta 2-receptor agonists, xanthines and Ca2+ antagonists in guinea-pig trachealis and seems compatible with K+ channel opening as a primary mode of relaxation for pinacidil in airway smooth muscle.

Relaxant effects of xanthines, a beta 2-receptor agonist and Ca2+ antagonists in guinea-pig tracheal preparations contracted by potassium or carbachol.

Potassium (124 mM K+ Krebs) produced a biphasic contractile response in the guinea-pig isolated trachea. An initial phasic contraction was followed by a larger and sustained contraction. Repeated potassium-induced contractions in spontaneously contracted guinea-pig tracheas were not reproducible. However, reproducible K+ responses were obtained in the presence of indomethacin (10(-6) M) that almost abolished the spontaneous tone. This suggested that endogenous cyclooxygenase products were variably released by K+ and interfered with its contractile effects. Both phases of K+-induced contractions were inhibited in Ca2+-free/EGTA Krebs. In contrast, about 80% of the contractile response to carbachol persisted in this medium. Tracheas contracted by potassium (indomethacin present) were completely relaxed by theophylline and enprofylline but only partly relaxed by terbutaline. All bronchodilators completely relaxed carbachol-contracted preparations. Each bronchodilator was 2-3 times less potent to relax K+- than carbachol-induced contractions. In sharp contrast, two Ca2+ antagonists, verapamil and nimodipine, preferentially relaxed K+-induced contractions. The results obtained with Ca2+ antagonists, which are poorly effective in asthma, compared to the established antiasthma drugs, xanthines and beta 2-receptor agonists, may indicate that depolarization-induced mechanisms contribute little to bronchoconstriction in asthma.

Smooth muscle relaxant effects of propofol and ketamine in isolated guinea-pig trachea.

The effects of anesthetics on airway smooth muscle tone are important in the management of patients with asthma. In the present study we evaluated the effect of propofol and ketamine on isolated guinea-pig tracheal preparations mounted for recording isometric contractile force. In a concentration-dependent way both drugs produced 100% relaxation irrespective of whether tracheal tone was spontaneous or induced by carbachol, histamine, prostaglandin F2 alpha, 30 mM K+ or 124 mM K+. The relaxant potency of propofol was dependent of the formulation of the drug used. Propofol showed an about 3 times higher potency when solubilized with hydroxypropyl-beta-cyclodextrin compared with an oil-in-water emulsion of the drug (Diprivan). Propofol had the greatest potency on tracheal preparations with spontaneous tone (EC50 = 4.0 +/- 0.9 microM). Ketamine preferentially relaxed contractions elicited by carbachol (EC50 = 120.8 +/- 5.2 microM) and had a lower potency than propofol when tone was spontaneous or induced by other tracheal spasmogens. Since propofol was a more effective tracheal relaxant in vitro than ketamine, the possibility that propofol, like ketamine, may inhibit bronchoconstriction during anesthesia should be studied further.

A comparison of the relaxant effects of pinacidil in guinea-pig trachea, aorta and pulmonary artery.

The relaxant activity of pinacidil, a proposed K+ channel opener, was compared in isolated guinea-pig trachea, aorta and pulmonary artery. In preparations precontracted by histamine or PGF2 alpha, pinacidil produced complete tracheal relaxation but only partial relaxation of vascular tissues. The order of responsiveness was: pulmonary artery greater than trachea greater than aorta. The slope of the pinacidil concentration-effect (C/E) curve was much steeper in the tracheal than in the vascular preparations. The pinacidil C/E curves for relaxation were similar when the three types of preparations were precontracted by 124 mM K+. Pretreatment with pinacidil caused a parallel shift of the tracheal histamine C/E curve to the right, whereas the maximal response to histamine was markedly depressed in the pulmonary artery.