Chronic thromboembolic pulmonary hypertension and mortality after venous thromboembolism: a nationwide population-based cohort study

Background

One of the ultimate long-term complications of venous thromboembolism (VTE) is chronic thromboembolic pulmonary hypertension (CTEPH). CTEPH is a condition defined as an increased mean pulmonary arterial pressure of at least 25 mmHg at rest and abnormal pulmonary artery resistance measured by right heart catheterization. To our knowledge, no study has compared mortality in VTE patients developing CTEPH to those who do not.

Purpose

We aimed to investigate the influence of CTEPH on long-term VTE mortality, by examining how receiving any pulmonary hypertension (PH) diagnosis following VTE influenced mortality.

Methods

We conducted a population-based cohort study of all adult Danish patients with an incident in or outpatient VTE diagnosis from 1995 through 2016. We excluded patients with a previous PH diagnosis. We defined CTEPH as receiving any PH diagnosis within two years following VTE. We categorized VTE by type (deep venous thrombosis [DVT] or pulmonary embolism [PE]) and provoking risk factors. We followed patients from two years after VTE until the first of death, emigration, or 31 December 2016. We calculated mortality rates and standardized mortality rate ratios (SMRs) of the association between PH and all-cause mortality and cause-specific mortality due to cancer and cardiovascular diseases. We also stratified the analyses by baseline presence of comorbidity (congestive heart failure, chronic pulmonary disease, and/or interstitial pulmonary disease).

Results

In 89,062 VTE patients alive two years after their VTE, 724 developed PH. The mortality rate per 1,000 person-years was 121 (95% confidence interval [CI]: 110–134) in patients with PH and 48 (95% CI: 47–48) in patients without PH. The SMR was 2.05 (95% CI: 1.77–2.37) for all VTE patients, 2.20 (95% CI: 1.53–3.16) for DVT patients, and 1.72 (95% CI: 1.47–2.01) for PE patients. The SMR was 1.79 (95% CI: 1.28–2.51) in VTE patients with a provoking VTE risk factor and 2.15 (95% CI: 1.83–2.53) in VTE patients without a provoking VTE risk factor. PH was associated with increased cause-specific mortality due to cardiovascular diseases (SMR=2.31, 95% CI: 1.75–3.06), but not cancer (SMR=0.94, 95% CI: 0.64–1.38). The SMR was 2.36 (95% CI: 2.06–2.71) in patients with comorbidity and 1.80 (95% CI: 1.45–2.24) in patients without comorbidity.

Conclusion

Development of PH, as a measure of CTEPH, within two years following incident VTE was associated with two-fold increased mortality in two-year VTE survivors. The increase in mortality was driven by cardiovascular causes.

Funding Acknowledgement

Type of funding sources: None.

Left atrial appendage occlusion versus standard of care in patients with atrial fibrillation and a prior thrombo-embolic event despite oral anticoagulant therapy: a propensity score matched comparison

Introduction

Patients with atrial fibrillation (AF) that suffer from ischemic stroke despite oral anticoagulant (OAC) therapy have a very high risk of recurrent stroke and better prevention strategies are needed. Left atrial appendage occlusion (LAAO) is a promising secondary prevention strategy that may provide mechanical protection in patients that suffer from thrombo-embolic events under OAC. However, evidence showing effectiveness of LAAO in this population is scarce and the current international guidelines only consider LAAO in patients with a contra-indication for OAC.

Purpose

To compare percutaneous LAAO to standard-of-care including continuing/switching anticoagulation therapy for secondary stroke prevention in patients with AF and a prior thrombo-embolic event and/or LAA thrombus under OAC therapy.

Methods

The STR-OAC LAAO cohort is an international collaboration combining a selection of patients from multiple LAAO registries (22 participating centers). Patients that underwent percutaneous LAAO because of a thrombo-embolic event and/or LAA thrombus on OAC were included. Propensity score matching (optimal matching method, 1:1 ratio) with a previously published multi-center dataset of patients continuing/switching anticoagulation treatment after a thrombo-embolic event was performed to adjust for imbalances in age, sex, hypertension, diabetes mellitus and CHA2DS2-VASc score. The primary outcome was ischemic stroke. Time-to-event analysis was performed with Kaplan-Meier curves and Cox-proportional-hazard regression analyses.

Results

A total of 404 patients underwent LAAO between 2010–2021 and were included in the STR-OAC LAAO cohort. Mean age was 72±9 years; 44% was female and mean CHA2DS2-VASc and HAS-BLED score were 4.8±1.7 and 2.5±1.4, respectively. Most patients received a Watchman or Amplatzer device (53% and 43%). Oral anticoagulation was discontinued after LAAO at discharge or after confirmation of adequate LAA closure at 1–3 months follow-up in 44% or 20%, respectively. The remaining 35% of patients continued OAC after LAAO as an adjunctive strategy. All LAAO patients were propensity-score matched and included in the primary outcome analysis. Baseline characteristics were well balanced after matching (Table 1). During follow up including 1406 patient-years (LAAO 1007; control 399) a total of 61 patients experienced an ischemic stroke: 2.2% per patient-year in LAAO group versus 9.8% per patient-year in the control group. LAAO was associated with a significantly lower risk of ischemic stroke (HR 0.33, 95% CI [0.19–0.59], p<0.001) compared to standard-of-care (Figure 1).

Conclusion

In this propensity-score matched study, LAAO was associated with a lower risk of ischemic stroke compared to standard-of-care in patients with a thrombo-embolic event and/or LAA thrombus despite OAC treatment. Randomized controlled trial data may further confirm the effectiveness of LAAO in this very high-risk population.

Funding Acknowledgement

Type of funding sources: None.

One-year results from the FLXibility post-approval study: final real-world clinical outcomes with a next-generation left atrial appendage closure device

Funding Acknowledgements

Type of funding sources: Private company. Main funding source(s): Boston Scientific Corporation, Marlborough, MA, USA

Background

The WATCHMAN FLX left atrial appendage (LAA) closure device received CE-mark and FDA approval based on the results of the PINNACLE FLX IDE study, but evidence of outcomes with this next-generation device in everyday clinical practise is limited.

Purpose

The FLXibility Post-Approval Study collected real-world data on patients implanted with a WATCHMAN FLX in a routine clinical practise.

Methods

Patients were implanted with a WATCHMAN FLX per local standard of care, with a subsequent first follow-up visit from 45-120 days post-implant and a final follow-up at 1 year post procedure. A Clinical Event Committee adjudicated all major adverse events and TEE/CT imaging results were adjudicated by a core laboratory.

Results

Among 300 patients enrolled at 17 centres in Europe, the mean age was 74.6±8.0 years, mean CHA2DS2-VASc score was 4.3±1.6, mean HAS-BLED score was 2.6±1.0, and 62.1% were male. The device was successfully implanted in 99.0% (297/300) of patients; 97.0% (289/298) required only 1 device for an implantation attempt and no patient required >2 devices. TEE was used for 78% of procedures and ICE for 22%. The post-implant medication regimen was DAPT for 87.3% (262/300). At first follow-up, among 170 patients with evaluable imaging, 87.6% (149/170) had no leak, 12.4% (21/170) had leak >0mm to ≤5mm with 16 (9.4%) of these <3mm, and no patient had leak >5mm, per core lab adjudication. At 1 year, 93.3% (280/300) patients had final follow-up or death. At final follow-up, 61% of patients were on a single antiplatelet medication, 21% were on DAPT, 6% were on a direct oral anticoagulation medication, and 12% were not taking any antiplatelet/anticoagulation medication. One-year all-cause mortality was 10.8% (32/295), among which 5.1% (15/295) were cardiovascular or unexplained. Disabling stroke occurred in 1.0% (3/295) of patients and nondisabling stroke also in 1.0% (3/295) of patients; all were nonfatal. No patient experienced a systemic embolism. Device-related thrombus was detected in 2.4% (7/295) patients. Pericardial effusion requiring surgery or pericardiocentesis occurred in 1.0% (3/295), with all of these events occurring in the first 7 days post-procedure. Cumulative BARC-3 or -5 bleeding occurred in 3.7% (11/300) of patients from 0 to 7 days, in 7.3% (22/300) at 6 months, and in 8.1% (24/295) patients at 1 year. One patient (0.3%) had a peri-procedural device embolisation, with no subsequent device embolisations or any device migration reported for any patient through 1 year.

Conclusions

The WATCHMAN FLX device had excellent procedural success rates, with high effective LAA closure rates and low serious adverse event rates in everyday clinical practise.

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.

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.

Effect of the oral hypoglycaemic sulphonylurea glibenclamide, a blocker of ATP-sensitive potassium channels, on walking distance in patients with intermittent claudication

AIMS

The oral hypoglycaemic sulphonylurea glibenclamide stimulates endogenous insulin secretion through blockade of ATP-sensitive potassium (KATP) channels on pancreatic beta cells, but also blocks cardiovascular KATP channels, leading to increased peripheral vascular resistance and reduced peripheral blood flow in non-diabetic subjects. Therefore, this study examined whether a single oral dose of glibenclamide adversely affected the pain-free or maximal walking distance in patients with intermittent claudication.

METHODS

In a double-blind, randomized crossover study, 12 non-diabetic patients with intermittent claudication were given a single oral dose of glibenclamide (5.25 mg) or placebo separated by a washout period of 1 week. A treadmill test was carried out 180 min after glibenclamide/placebo intake for determination of pain-free and maximal walking distance. Plasma glucose concentrations were kept constant by an euglycemic clamp. Changes in ankle/brachial blood pressure index (ABI), serum insulin, and serum glibenclamide were also assessed.

RESULTS

The pain-free walking distance was 62.8 +/- 9.8 metres (mean +/- sem) after glibenclamide and 52.6 +/- 5.9 metres after placebo (P = 0.52). The maximal walking distance was 142.7 +/- 18.7 metres after glibenclamide and 132.6 +/- 16.6 metres after placebo (P = 0.23). The ABI was not significantly changed by glibenclamide compared with placebo. Serum glibenclamide was 0.51 +/- 0.08 microm 180 min after administration of the drug. Glibenclamide produced an 8-fold increase in circulating insulin compared with placebo (P < 0.001).

CONCLUSIONS

Glibenclamide given as a single oral dose commonly used in glucose-lowering drug therapy does not reduce pain-free or maximal walking distance in non-diabetic patients with intermittent claudication.

Ischaemic preconditioning does not protect the heart in obese and lean animal models of type 2 diabetes

AIMS/HYPOTHESIS

The prevalence of type 2 diabetes mellitus is increasing worldwide with obese diabetic patients constituting the majority of this population. Type 2 diabetes is associated with increased morbidity and mortality after acute myocardial infarction. Previous experimental studies of ischaemia-reperfusion tolerance in diabetes have only been performed in animal models of type 1 diabetes mellitus, yielding conflicting data. The aim of the present study was to characterise and compare the tolerance to ischaemia and effects of ischaemic preconditioning (IPC) in hearts from obese Zucker diabetic fatty (ZDF) and lean Goto-Kakizaki (GK) type 2 diabetic rats, using non-obese Zucker and Wistar rats as respective controls.

METHODS

The two rat strains were divided into 8 groups. The ZDF study (n=47) consisted of: Control -IPC, Control +IPC, ZDF -IPC and ZDF +IPC. The GK study (n=38) consisted of: Control -IPC, Control +IPC, GK -IPC and GK +IPC. Hearts, which were studied in a Langendorff preparation perfused with Krebs-Henseleit buffer, were subjected or not to IPC (+IPC, -IPC) before 50 minutes of regional ischaemia and 120 minutes reperfusion.

RESULTS

Ischaemic reperfusion injury was smaller in obese (p<0.05) and lean (p<0.05) type 2 diabetic animals than in their respective control animals. IPC reduced ischaemic reperfusion injury during reperfusion in non-diabetic control rats (p<0.01), but failed to protect hearts from both diabetic animal models. Post-ischaemic haemodynamic recovery was impaired in the ZDF rats compared to both control and GK rats (p<0.05).

CONCLUSIONS/INTERPRETATION

Ischaemic preconditioning does not protect hearts from obese or lean type 2 diabetic animals. However, the susceptibility of the type 2 diabetic myocardium to ischaemic damage is lower than in non-diabetic hearts. The method described here could be used as a tool to study the pathogenesis of increased cardiovascular morbidity and mortality in type 2 diabetes.

[Spontaneous dissection of the left main coronary arteries in three women]

Spontaneous dissection of the coronary artery is a rare cause of sudden death and myocardial infarction. We report three cases in women aged 32, 38, and 55 years. One patient was one week post partum. In one case all three coronary arteries were involved. Two patients underwent coronary artery bypass grafting and one died of acute heart failure. The epidemiology, aetiology, and clinical manifestations are briefly described. We suggest that coronary angiography should be considered in young women with acute myocardial infarction and few risk factors of atherosclerosis.

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.

Vascular smooth muscle contraction is an independent regulator of endothelial nitric oxide production

This investigation was conducted to determine whether endothelial nitric oxide (NO) production is regulated by vascular smooth muscle contraction. Unperfused ring segments of rat aorta and mesenteric artery were studied using isometric tension recording (n = 6-8 in all experiments). Following a reference contraction to K+ 80 mM (100%), arteries were left either unstimulated or stimulated by different concentrations of K+ or prostaglandin F2alpha (PGF2alpha) to induce different levels of vascular precontraction. N(G)-nitro-L-arginine methyl ester (L-NAME 0.1-300 microM) or NS 2028 (0.03-3 microM), which is a new specific inhibitor of the NO-sensitive guanylate cyclase, was then added at increasing concentrations to evaluate endothelial NO production. L-NAME and NS 2028 produced a concentration-dependent vasoconstrictor response which was progressively enhanced with increasing levels of precontraction. For L-NAME, this amounted in aorta to (% of reference contraction): 35+/-1% and 105 +/- 4% (precontraction by K(+) 20 and 30 mM) and 22+/-1%, 89+/-1%, 138+/-1% and 146+/-2% (precontraction by PGF2alpha 0.5, 1, 2 and 3 microM). A similar coupling was found in the mesenteric artery. A precontraction as little as 2% was enough to trigger a vasoconstrictor response to L-NAME. In contrast, L-NAME and NS 2028 had no effect in non-contracted arteries, not even when passive mechanical stretch was increased by 100%. The results suggest (i) that endothelial NO formation is progressively increased with increasing vascular tone, and (ii) that vascular isometric contraction per se stimulates endothelial NO formation. It is concluded, that active vascular smooth muscle contraction is an independent regulator of endothelial NO production.

Hydralazine-induced vasodilation involves opening of high conductance Ca2+-activated K+ channels

The purpose of this study was to investigate whether high conductance Ca2+-activated K+ channels (BK(Ca)) are mediating the vasodilator action of hydralazine. In isolated porcine coronary arteries, hydralazine (1-300 microM), like the K+ channel opener levcromakalim, preferentially relaxed contractions induced by K+ (20 mM) compared with K+ (80 mM). In addition, concentration-relaxation curves for hydralazine (pD2 = 5.38 +/- 0.06; Emax = 85.9 +/- 3.6%) were shifted 10-fold to the right by the BK(Ca) blockers tetraethylammonium (1 mM) and iberiotoxin (0.1 microM). In contrast, nimodipine (a Ca2+-entry blocker), relaxed contractions induced by K+ (20 mM) and K+ (80 mM) equally and nimodipine-induced relaxations were neither antagonized by tetraethylammonium nor by iberiotoxin. In isolated perfused rat hearts, hydralazine (1 microM) increased coronary flow by 28.8 +/- 2.7%. Iberiotoxin (0.1 microM) suppressed this response by 82% (P < 0.05). In conscious, chronically catheterized rats the hypotensive response to hydralazine (0.6 mg kg(-1) min(-1)) was significantly reduced by 41% during infusion of iberiotoxin (0.1 mg kg(-1)). It is concluded, that opening of BK(Ca) takes part in the mechanism whereby hydralazine produces vasodilation.

Inducible nitric oxide synthase (iNOS) in the human heart: expression and localization in congestive heart failure

The inducible nitric oxide (NO) synthase (iNOS or NOS2) generates a prolonged release of large amounts of NO which may be cytotoxic and/or inhibit myocyte contractility. It has been suggested that this mechanism specifically contributes to heart failure caused by dilated cardiomyopathy (DCM). To test this hypothesis we compared the myocardial amount and localization of iNOS in myocardial biopsies from patients with heart failure caused by either DCM or ischemic heart disease (IHD). During heart transplantation, myocardial biopsies collected from the diseased heart after explantation were frozen in liquid nitrogen. Twenty-two patients in NYHA class III-IV were included (DCM: n = 8; IHD: n = 14). In each biopsy, iNOS expression was assessed using reverse transcription polymerase chain reaction (RT-PCR), and visualized by immunohistochemistry. iNOS was detected in all biopsies. Intriguingly, the amount of iNOS mRNA (shown as iNOS cDNA normalized to GADPH cDNA) did not differ significantly between the two groups (DCM 30 +/- 7; IHD 20 +/- 6, mean +/- S.E.M., P > 0.05). Similarly, no inter-group differences in the amount of iNOS protein (Western) were observed. iNOS was invariably located to vascular endothelial and smooth muscle cells. In addition, an iNOS reaction in relation to the myocyte membrane was found in 4 of the 22 patients. These four patients (two from each group) had significantly (P < 0.05) higher iNOS/GADPH ratios (54 +/- 20) than patients without myocyte membrane iNOS reaction (17 +/- 15). In conclusion, iNOS is expressed in the myocardium of all patients with heart failure caused by either DCM or IHD. iNOS is located primarily and invariably in the endothelium and vascular smooth muscle cells of the myocardial vasculature and its expression appears to be associated with the condition of heart failure per se rather than related to the heart failure etiology.

Coronary vasorelaxant effect of levosimendan, a new inodilator with calcium-sensitizing properties

We examined the action of levosimendan, a new Ca2+-sensitizing inodilator, on isolated porcine coronary arteries. Vessel rings were studied in isometric myographs. Arterial cyclic adenosine monophosphate (cAMP) levels were determined by radioimmunoassay. Levosimendan (10(-7)-10(-3) M) completely relaxed arteries preconstricted by prostaglandin F2alpha (PGF2alpha) with a pD2 (-logEC50) value of 3.99 +/- 0.05 (n = 6-9 in all experiments). Pretreatment with levosimendan also prevented contraction induced by PGF2alpha. The vasorelaxation produced by levosimendan (10(-7)-10(-3) M) was not attenuated by removal of the endothelium. Levosimendan (10(-7)-10(-3) M) relaxed contractions induced by 30 mM K+ as well as 80 mM K+, whereas the K+ channel opener levcromakalim selectively relaxed contraction induced by 30 mM K+. Neither the cyclooxygenase inhibitor indomethacin nor the beta-adrenoceptor blocker propranolol influenced levosimendan-induced vasorelaxation. The Ca2+-entry blocker isradipine failed to relax arteries precontracted by endothelin-1 in Ca2+-free/EGTA medium. However, levosimendan (10(-7)-3 x 10(-3) M) completely relaxed endothelin-1-induced contractions in this medium. Levosimendan potentiated the relaxant effect of a cAMP-stimulating drug, isoprenaline, but also that of nitroglycerin and isradipine. At a maximal effective concentration, it increased arterial tissue contents of cAMP twofold. In conclusion, levosimendan produces coronary vasorelaxation by a mechanism that seems to be endothelium independent and not mediated by K+ channel opening, Ca2+-entry blockade, release of cyclooxygenase products, or beta-adrenoceptor stimulation. Accumulation of cAMP may possibly participate in vasorelaxation at high concentrations of levosimendan, but a cAMP-independent mechanism seems to be involved at lower concentrations.

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.

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.

Potassium channel modulation: a new drug principle for regulation of smooth muscle contractility. Studies on isolated airways and arteries

K+ channels play a key role in regulation of membrane potential and cell excitability. Several different types of K+ channels have been identified and the presence, characteristics and functions of these channels vary among different tissues. The 3 most important K+ channels in smooth muscle are the KATP (activated by a fall in intracellular ATP and a rise in nucleotide diphosphates and blocked by glibenclamide), BKCa (activated by a rise in intracellular Ca2+) and Kv (activated by depolarization). Cromakalim, pinacidil and nicorandil are members of a rapidly increasing group of novel drugs which open K+ channels. Opening of such channels leads to K+ efflux, membrane hyperpolarization, reduced excitability and smooth muscle relaxation. The purpose of the studies included in this thesis was to investigate this novel drug principle of K+ channel modulation on smooth muscle contractility of isolated airways and arteries and on neuroeffector transmission in airways. Smooth muscle contractility was measured in airway and vascular ring preparations suspended in isometric myographs. Neurotransmitter release was elicited by transmural electrical field stimulation. The major findings were: 1) Membrane depolarization by high extracellular K+ concentrations induced contraction of airway smooth muscle that was easily relaxed by Ca2+ antagonists and abolished in a Ca2+ free medium indicating that K+ contraction is triggered by Ca2+ influx through voltage-operated Ca2+ channels. Indomethacin was required to obtain reproducible responses upon repeated exposure to K+ suggesting that endogenous prostaglandins are released by K+ and interferes with its contractile effect. K+ depolarization was shown to be a valuable pharmacological tool for detection of drugs acting by K+ channel opening. The prototype K+ channel opener cromakalim relaxed contractions induced by 20-30 mM K+ but had no effect against contraction induced by 124 mM K+. This was a unique profile of action not shared by other types of airway and vascular smooth muscle relaxants. As the extracellular K+ concentration is raised the outward directed electrochemical gradient for K+ is reduced and at high K+ concentrations the effect of K+ channel opening is negligible. Although the K+ channel opener pinacidil had a higher relaxant potency against contraction induced by 30 mM K+ than by 124 mM K+, it still relaxed the latter contraction indicating an additional K+ channel independent mechanism of action of the drug. When K+ depolarization is used as a pharmacological tool, it is essential to maintain osmolarity. Addition of KCI directly to the tissue bath solution, which previously was a commonly applied technique, produced confounding and unwanted effects due to hyperosmolarity per se. 2) Pinacidil and cromakalim relaxed guinea-pig trachea either tone was spontaneous or induced by a range of airway spasmogens (histamine, PGF2 alpha, LTC4/LTD4 or carbachol) of relevance as asthma mediators. The relaxant effectiveness of the drugs was reduced when tone was elicited by carbachol. The airway smooth muscle relaxation produced by pinacidil and cromakalim was selectively blocked by the antidiabetic sulfonylureas glibenclamide, glipizide and glibornuride and also by phentolamine. These drugs are blockers of KATP which therefore indicates that this channel is the target for cromakalim and pinacidil in airway smooth muscle. Additional to the antagonistic action against K+ channel openers the sulfonylurea KATP blockers and phentolamine at higher concentrations relaxed airway smooth muscle by yet unknown mechanisms that seemed unrelated to KATP. 3) Cromakalim and pinacidil inhibited nerve-mediated e-NANC contractile responses in guinea-pig bronchi. Such responses are due to release of SP and related tachykinins from sensory nerve endings. These neuropeptides cause bronchoconstriction and airway inflammation and may possibly play an important role in the pathophysiology of asthma.

In vivo nitrate tolerance is not associated with reduced bioconversion of nitroglycerin to nitric oxide

BACKGROUND

In vitro data suggest that reduced bioconversion of nitroglycerin (NTG) to nitric oxide (NO) contributes to the development of vascular and hemodynamic tolerance to NTG. We examined the in vivo validity of this hypothesis by measuring NTG-derived NO formation by in vivo spin-trapping of NO in vascular tissues from nitrate-tolerant and -nontolerant rats.

METHODS AND RESULTS

Five groups (n = 6 to 8 each) of conscious chronically catheterized rats received NTG (0.2 or 1 mg/h IV) for 72 hours (nitrate-tolerant groups). Four other groups received either NTG vehicle (placebo, for 72 hours) or were left untreated (control). Nitrate tolerance was substantiated by a reduced (55% to 85%) hypotensive response to NTG in vivo and a reduced relaxation to NTG in isolated aortic rings. NTG-derived NO formation in aorta, vena cava, heart, and liver was measured as NOFe(DETC)2 and NO-heme complexes formed in vivo during 35 minutes combined with ex vivo cryogenic electron spin resonance spectroscopy. NO formation was significantly (P < .05) increased in all tissues in nitrate-tolerant rats in an NTG dose-dependent manner. Furthermore, the amount of NO formed from a bolus dose of NTG (6.5 mg/kg over 20 minutes) was similar in nitrate-tolerant and -nontolerant rats.

CONCLUSIONS

The results suggest that vascular and hemodynamic NTG tolerance occurs despite high and similar rates of NO formation by NTG in tolerant and nontolerant target tissues. This finding is compatible with the assumption that reduced biological activity of NO, rather than reduced bioconversion of NTG to NO, contributes to in vivo development of nitrate tolerance.

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.

Inhibition by cromakalim, pinacidil, terbutaline, theophylline and verapamil of non-cholinergic nerve-mediated contractions of guinea-pig isolated bronchi

Contractions induced by electrical field stimulation of sensory non-cholinergic excitatory nerves in guinea-pig isolated bronchi are due to the release of substance P (SP) and related tachykinins. Release of such neuropeptides are thought to play a pathophysiological role in asthma. Two K+ channel openers cromakalim (pD2 = 6.45; Emax = 95%) and pinacidil (pD2 = 6.06; Emax = 87%) were shown to concentration-dependently inhibit non-cholinergic nerve-mediated contractions in guinea-pig bronchi in vitro. Cromakalim (pD2 = 6.27; Emax = 25%) and pinacidil (pD2 = 6.03; Emax = 25%) each had a much lower inhibitory efficacy against contractions induced by exogenously applied SP but the same potency as found against contractile responses to non-cholinergic neurostimulation. Also the beta 2-adrenoceptor agonist terbutaline (pD2 = 8.29; Emax = 83%), the xanthine derivative theophylline (pD2 = 4.19; Emax = 100%) and the Ca2+ blocker verapamil (pD2 = 5.55; Emax = 100%) suppressed responses to non-cholinergic neurostimulation. Terbutaline (pD2 = 6.32; Emax = 74%), theophylline (pD2 = 3.25; Emax = 71%) and verapamil (pD2 = 4.01; Emax = 100%) had a 10-100-fold lower inhibitory potency against SP-induced contractions but each drug showed about the same efficacy as found against nerve-mediated contractions. Glibenclamide (1 microM) reversed the inhibitory effects of cromakalim and pinacidil on neurally-mediated contractions but did not influence the effects of terbutaline, theophylline and verapamil. The results demonstrate that cromakalim, pinacidil, terbutaline, theophylline and verapamil inhibit non-cholinergic excitatory neurotransmission in guinea-pig bronchi and suggest that they act preferentially at a pre-junctional site.

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)

[Cardiac risk in surgery. A review and guidelines for risk evaluation and reduction of cardiac risk in general surgery]

Cardiac complications occur with an incidence of 2-6% and are a main cause (15-20%) of mortality after non-cardiac surgery. Cardiac risk should be determined and reduced by treatment preoperatively and by an intraoperative and postoperative care that has been adjusted to the increased risk. This review provides recommendations concerning risk evaluation and management.

[Ventricular fibrillation and cardiac aneurysms caused by sarcoidosis]

A 27-year-old woman presented during a football match with sudden cardiac arrest due to ventricular fibrillation. After electrical defibrillation the electrocardiogram showed sinus rhythm with left bundle branch block. Ventriculography, echocardiography and magnetic resonance imaging revealed an aneurysm in the basal part of the ventricular septum and another aneurysm on the anterior wall of the right ventricle. She had normal coronary arteries. Ventricular tachycardia was induced in the outflow tract of the right ventricle during electrophysiological study. She was treated surgically by aneurysmectomy and cryocoagulation. No ventricular tachyarrythmia could be provoked at postoperative electrophysiological testing. Histological examination of the right ventricular aneurysm showed the presence of noncaseating granulomas and scar tissue consistent with cardiac sarcoidosis. She had no other systemic manifestations of the disease. The patient was doing well and had no cardiac symptoms after the operation. She died suddenly of unknown cause 21 months later. No autopsy was performed.

Effects of antidiabetic sulphonylureas, cromakalim and their interaction in guinea-pig isolated tracheal smooth muscle

Glibenclamide, glipizide and glibornuride showed dual effects in guinea-pig isolated trachea. The drugs antagonized the relaxant response to the K+ channel opener cromakalim (order of effectiveness: glibenclamide > glipizide > glibornuride) and at concentrations of 1-1000 microM produced airway smooth muscle relaxation (order of potency: glibenclamide > glipizide = glibornuride). Gliclazide, tolbutamide and chlorpropamide did not antagonize cromakalim nor did the two latter drugs produce tracheal relaxation. The sulphonylureas and cromakalim were compared as airway relaxants against a panel of different spasmogens. The order of tissue responsiveness for the sulphonylureas was: spontaneous tone = LTD4 > PGF2 alpha = histamine = 30 mM K+ > carbachol and for cromakalim: spontaneous tone = LTD4 = PGF2 alpha = histamine > carbachol > 30 mM K+. Glibenclamide, but not cromakalim, relaxed contractions induced by 124 mM K+. Phentolamine and Ba2+, which are reported blockers of ATP-regulated K+ channels, failed to influence sulphonylurea-induced airway smooth muscle relaxation. Glibenclamide reversed tracheal relaxation produced by cromakalim, whereas cromakalim failed to reverse relaxation induced by glibenclamide. The mechanism for the additional property of sulphonylureas to relax airway smooth muscle is unclear, but the results do not support a role for involvement of cromakalim-sensitive K+ channels.

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.

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.

Influence of osmolarity of solutions used for K+ contraction on relaxant responses to pinacidil, verapamil, theophylline and terbutaline in isolated airway smooth muscle

Concentration-relaxation profiles for pinacidil, verapamil, terbutaline and theophylline were studied in guinea-pig trachealis contracted by two commonly applied techniques for K+ depolarization. All drugs were much less effective on contractions induced by hyperosmolar 124 mMn K+ solution (added KCl) than on contractions elicited by an isoosmolar 124 mM K+ Krebs solution (substituted KCl). The maximal relaxant responses were (isoosmolar K+/hyperosmolar K+): pinacidil 100%/40%, verapamil 100%/60%, theophylline 100%/0%, terbutaline 50%/0%. Addition of mannitol to establish the same hyperosmolarity as with 124 mM KCl also produced contraction of guinea-pig trachealis. Concentration-relaxation curves for the drugs on mannitol-induced contractions had close resemblance to those obtained in hyperosmolar 124 mM K+ solution. When contraction was elicited by 30 mM K+, pinacidil showed seven times higher relaxant potency in hyperosmolar compared to isoosmolar solution, whereas the relaxant responses to verapamil, theophylline and terbutaline were not influenced by osmolarity. When K+ depolarization is used as a tool for evaluation of drug action in airway smooth muscle, the two different techniques produce dissimilar results. The influence of hyperosmolarity per se appears to be an important and unwanted feature when K+ depolarization is produced by addition of KCl.

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.

[Pulmonary edema induced by hydrochlorothiazide/amiloride (Moduretic)]

A 44-year-old woman was seen on three separate occasions for acute pulmonary edema which had developed 30 minutes after ingestion of a single hydrochlorothiazide-amiloride (Moduretic) tablet. Eighteen cases of hydrochlorothiazide-induced pulmonary edema have been reported previously. Clinical findings and investigations in the present and previous cases indicate a noncardiogenic cause for the pulmonary edema. Increased pulmonary vascular permeability is probably involved. So far, attempts to demonstrate an immunological mechanism have failed and the pathophysiology remains uncertain. The reaction may be difficult to differentiate from left ventricular failure in patients with cardiac disease. Attention should be drawn to this severe but rare side effect of a frequently used diuretic.

Differential relaxant responses to pinacidil of smooth muscle preparations contracted by a high concentration of potassium in isoosmolar and hyperosmolar solutions

Contractions were produced in guinea-pig trachealis, aorta and pulmonary artery by depolarization with 124 mM K+ using two commonly applied techniques. Addition of KCl to the organ bath solution making it hyperosmolar induced slowly developing contractions, which were only weakly inhibited by pinacidil. Hyperosmolar mannitol-induced contractions showed similar characteristics. In contrast, contractions elicited by isoosmolar K+ Krebs solution developed more rapidly and could be completely suppressed by pinacidil (10(-6)-10(-3) M) in a concentration-dependent manner. The findings explain previously published discrepant results on the relaxant response to pinacidil of smooth muscle preparations contracted by high concentrations of K+, and indicate other mechanisms of action for pinacidil in addition to K+ channel opening, in the concentration range 10(-6)-10(-3) M.

Lack of effect of pinacidil on theophylline pharmacokinetics and metabolism in man

Pinacidil, a pyridyl cyanoguanidine derivative, is a new antihypertensive vasodilator drug. It shares structural similarities with the histamine H2-receptor blocker cimetidine, an imidazole cyanoguanidine derivative, which is a potent inhibitor of cytochrome P-450 and of theophylline metabolism. In the present study the pharmacokinetics and metabolism of theophylline were determined in six healthy volunteers before and on the last day of oral pinacidil administration for two weeks. The dosage of pinacidil was 12.5 mg twice a day in the first week and 25 mg in the second. There were no significant changes in theophylline plasma clearance, terminal half-life or volume of distribution during pinacidil administration. Also the renal and metabolic clearance of theophylline and the formation clearances of the major theophylline metabolites in the urine (DMU, 1MU, 3MX) did not change significantly during administration of therapeutic doses of pinacidil.

Glibenclamide blocks the relaxant action of pinacidil and cromakalim in airway smooth muscle

Concentration-relaxation curves for pinacidil and cromakalim were obtained in isolated guinea-pig tracheas contracted by histamine. Pinacidil produced complete relaxation with an EC50 value of 2.8 microM. The antidiabetic sulfonylurea, glibenclamide (0.1, 1, 10 microM), caused concentration-dependent rightward shifts (3- to 16-fold) of the concentration-relaxation curve for pinacidil without changing the maximal relaxant response. Cromakalim produced 85% relaxation with an EC50 value of 1.1 microM. Glibenclamide (0.1 microM) displaced the concentration-relaxation curve to the right and at higher concentrations (1-10 microM) caused nearly complete suppression of the maximal relaxant response to cromakalim. Glibenclamide not only prevented the effects of pinacidil and cromakalim but also produced a concentration-dependent and complete reversal of submaximal relaxations produced by these drugs. Glibenclamide was a selective antagonist of the relaxation of airway smooth muscle induced by pinacidil and cromakalim. Concentration-relaxation curves for theophylline, terbutaline and verapamil were unaffected by glibenclamide.

[Fatal hepatitis caused by disulfiram]

A case of fatal fulminant hepatitis following treatment with disulphiram in a man aged 34 year is reported. Acute toxic hepatitis produced by disulphiram is a rare but serious side effect with a lethality about 40%. In the case reported here, immediate withdrawal of disulphiram administration on the earliest signs of hepatitis did not prevent toxic development of severe hepatic necrosis.

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.

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.

Verapamil-induced inhibition of theophylline elimination in healthy humans

The interaction between theophylline and verapamil was investigated in 7 healthy volunteers. Oral administration of verapamil in a dose of 120 mg t.i.d. for 7 days caused a significant inhibition of the elimination of theophylline (5 mg/kg intravenously). Theophylline clearance was reduced from 45.2 to 36.1 ml/hr/kg (20.1%; P less than 0.005). The apparent steady-state volume of distribution of the drug was not influenced. The terminal half-life of theophylline was increased from 6.80 to 8.23 hr (21.0%; P less than 0.001). Increased steady-state plasma theophylline concentrations may thus be expected when verapamil is added to a drug regimen which includes theophylline.

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.

Inhibition of theophylline elimination in rabbits by verapamil

Single intravenous dose pharmacokinetics of theophylline in 10 rabbits were investigated before and after 5 days oral administration of verapamil in daily doses of 6 mg/kg. Verapamil caused a significant inhibition of theophylline elimination. Theophylline clearance was reduced from 126 to 98 ml/hr/kg (22.2%) whereas the steady state volume of distribution of the drug increased from 461 to 550 ml/kg (19.3%). The terminal half-life of theophylline increased from 2.7 to 4.0 hr (49.8%).

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.

Pharmacodynamics and pharmacokinetics of enprofylline and theophylline in the isolated rabbit heart

The direct effects of theophylline and enprofylline, a new anti-asthma xanthine derivative without adenosine receptor blocking action, were studied in the isolated, spontaneously beating rabbit heart. At increasing concentrations from 2 x 10(-5)-5 x 10(-4) M both drugs produced increases in heart rate up to 143% and 162% and in contractility up to 135% and 147% from control values (100%), respectively. At concentrations higher than 10(-3) M contractures and heart block occured. Enprofylline showed a potency about 2.3 times higher than theophylline. Coronary flowrate did not increase. Myocardial oxygen consumption was moderately increased by the drugs. The myocardial pharmacokinetics showed two-compartment characteristics for both drugs. Half-times of the two phases of accumulation were for theophylline 0.28 and 0.98 min. and for enprofylline 0.31 and 0.78 min. The terminal disposition half-time for enprofylline was, however, 2.7 times higher than that of 0.91 min. for theophylline, apparently due to a stronger binding of the former drug intracellularly. Both xanthines accumulated against a concentration gradient showing myocardial tissue-perfusion liquid ratios of about 2.9 for theophylline and 3.7 for enprofylline. The drugs seem to exert their primary action on sarcolemmal binding sites which probably are unrelated to adenosine receptors.

A strain-gauge myograph for isometric measurements of tension in isolated small blood vessels and other muscle preparations

Isometric tension measurements in vitro on small vessels are important in studies of pharmacodynamic vascular effects of drugs and autacoids. The present study describes a precision myograph equipped with a newly constructed highly isometric strain-gauge transducer used in conjunction with a very sensitive, low-noise and virtually drift-free dc-amplifier. The isometric quotient of the transducer, defined as deflection in micrometer per g of force, is about 5.2. The transducer resonance frequency is 341 c/sec with a damping constant of 1.05. The highest sensitivity of the transducer in connection with the matching dc-amplifier is about 170 mV/V/g force. The practical working range of the myograph is from 2 mg to about 10 g of applied tensile force. Tubular segments of vessels with internal diameters down to 150 micron can be mounted in the myograph on two stainless-steel pins submerged in a 5 ml preparation bath. Precise mounting and setting of passive (resting) tension is assured by the use of micrometer-equipped adjustable miniature mounting tables suspended by roller bearings. The myograph may be provided with electrodes for field-effect stimulation of the vessel preparations. Other muscle preparations may also be mounted in the myograph. Application of the myograph in studies on rabbit coronary arteries is demonstrated by a length-tension diagram obtained in experiments with tubular segments (inner diameter about 500 micron) of the circumflex branch on the left coronary artery, which shows a typical course in development of active and passive tension of the smooth musculature when exposed to alternating potassium depolarization and increasing mechanical stretching. The potassium contracture of the coronary vessels and the log-concentration/response relationship at accumulating potassium concentrations were also investigated.

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.

Enprofylline and theophylline on small human placental arteries: studies of in vitro effects and mode of action

Vascular effects of theophylline and enprofylline, a novel xanthine derivative lacking adenosine receptor antagonism, were studied comparatively in tubular preparations of small human placental arteries mounted in an isometric myograph. Both xanthines produced concentration-dependent (10(-7)-3 X 10(-3) M) relaxation of arteries contracted by PGF2 alpha or PGE2 in both normal Ca2+-medium and in Ca2+-depleted medium. Enprofylline was about three times more potent than theophylline. Also in vasopressin-contracted arteries enprofylline was a more potent vasodilator in both media. In contrast the xanthines were equally potent in relaxation of the tonic as well as the phasic part of a K+-induced contraction, but less potent than in relaxation of PG-induced contractions. Propranolol, phentolamine, atropine, indomethacin or tetrodotoxin did not influence the xanthine relaxations. It is concluded that the theophylline-induced relaxation of small human placental arteries is not due to adenosine receptor antagonism. A common important mechanism of action, in which enprofylline is more potent than theophylline, seems to be interference with intracellular Ca2+-binding/mobilisation processes. Some decrease in cellmembrane Ca2+-permeability produced by the xanthines seems to take part in the mechanism of relaxation.

Effects of theophylline on small human placental arteries in vitro

Effects of theophylline on contractions induced by relevant physiological agents in tubular segments of small human placental arteries were measured in an isometric myograph. Theophylline 10(-7) - 3 X 10(-3)M caused marked relaxation of steady contractions produced by prostaglandin F2 alpha (PGF2 alpha), prostaglandin E2 (PGE2), vasopressin or potassium. EC50 for theophylline relaxation of the PGF2 alpha - contraction was 1.6 X 10(-4) M. Emax was 91.5% relaxation. Theophylline was less potent in relaxing the potassium induced contraction. Pretreatment experiments with 10(-4) and 10(-3)M theophylline showed a pronounced decrease in contractile Emax-values for PGF2 alpha, PGE2 and vasopressin as a possible indication of non-competitive antagonism. The results motivate further studies to elucidate possible effects of theophylline and other xanthines on the vascular resistance and blood flow in placenta.