KATP channel modulation in working rat hearts with coronary occlusion: effects of cromakalim, cicletanine, and glibenclamide.

OBJECTIVES: We studied the effects of ATP-sensitive potassium channel (KATP) modulation on ischemic cardiac performance and reperfusion-induced ventricular fibrillation (VF), and assessed the contribution of KATP to the cardioprotective and anti-arrhythmic effect of the anti-hypertensive drug cicletanine. METHODS: Isolated working rat hearts, subjected to a 10-min coronary occlusion followed by reperfusion, were perfused in the presence of vehicle, 0.1-60 microM cromakalim, an opener of KATP; 3-60 microM cicletanine; and 0.1-10 microM glibenclamide, a blocker of KATP, respectively. RESULTS: All concentrations of cicletanine, similarly to 0.1-10 microM cromakalim, attenuated ischemia-induced deterioration of aortic flow, left ventricular developed pressure, and left ventricular end-diastolic pressure. In contrast to cromakalim, cicletanine did not increase coronary flow. Cicletanine (60 microM) and cromakalim (10 and 60 microM) significantly reduced the incidence of reperfusion-induced VF; however, 60 microM cromakalim triggered VF during ischemia. Lower concentrations of cromakalim and cicletanine did not produce an anti-arrhythmic effect. Cardiac functional parameters were concentration dependently worsened by glibenclamide, and the drug did not change the incidence of VF. Glibenclamide (0.1 microM) did not significantly affect cardiac performance, but it did abolish the anti-ischemic effect of cromakalim (1-10 microM) and cicletanine (60 microM). Glibenclamide suppressed the anti-arrhythmic effect of 10 and 60 microM cromakalim; however, it did not affect the anti-arrhythmic effect of cicletanine. CONCLUSIONS: (i) The anti-ischemic but not the anti-arrhythmic effect of cicletanine may involve opening of KATP. (ii) opening of KATP attenuates, inhibition of the channel exacerbates functional consequences of coronary occlusion, and (iii) KATP opening attenuates reperfusion-induced VF, but it triggers ischemia-induced VF. KATP blocking does not affect VF.

UV-C irradiation-induced peroxidative degradation of microsomal fatty acids and proteins: protection by an extract of Ginkgo biloba (EGb 761).

After exposure of rat liver microsomes to UV-C irradiation, analysis of membrane fatty acids by gas chromatography confirmed that EGb 761, a drug containing a dosed and standardized extract of Ginkgo biloba, provides effective protection against free radical attack in vitro. This analysis, coupled with thiobarbituric acid (TBA) reaction, permitted qualitative and overall quantitative evaluation of radical-induced damage to polyunsaturated fatty acids (PUFA), as well as evidence of the antioxidant properties of the Ginkgo biloba extract. Assay of thiobarbituric acid reactive substances (TBARS) showed a correlation between TBARS concentration and the state of degradation of the polyunsaturated fatty acids. Mannitol (5.5 mM) did not prevent degradation of microsomal PUFA or malondialdehyde (MDA) production, nor did it prevent polymerization of membrane proteins. Low doses of EGb 761 were found to provide efficient protection of membrane PUFA regardless of individual susceptibility to peroxidation. This protection was accompanied by a decrease in the production of TBARS. EGb 761 also protected membrane proteins from the irreversible polymerization induced by these degradation products, but did not appear to prevent thiols oxidation into disulfide bonds.

Pharmacokinetics and organ distribution of the sorbin C-terminal peptides.

Sorbin is a 153 amino acid peptide isolated from porcine small intestine. The heptapeptide-amide is the minimal active site of the natural molecule. A comparison of the distribution of C-7 and C-20 sorbin, which have been shown to share the activity of sorbin in increasing intestinal absorption of electrolytes, was undertaken by radioimmunoassay, after perfusion of 200 micrograms/kg/h. A longer half-life in plasma was observed for C-20 sorbin than for C-7 sorbin, with a clearance rate of 18 +/- 4 ml/min/kg vs. 40.6 +/- 13.5 ml/min/kg and a distribution volume of 192 +/- 35 ml/kg vs. 286 +/- 123 ml/kg. The accumulation of tritiated C-7 sorbin was observed in enterocytes, serosal acini of the salivary glands, and fundus chief cells. The recovery of intact peptide in the intestine was 0.06% per gram of tissue. Eighteen percent of the peptide was detected in urine.

Immunometric assay of BN 52080, a heptapeptide C-terminal analogue of sorbin.

A novel type of enzyme immunometric assay has been developed for a heptapeptide, BN 52080. This compound is a short C-terminal analogue of sorbin and is under clinical evaluation for treatment of chronic diarrhea. In this solid-phase immobilized epitope immunoassay (SPIE-IA), the peptide is first immunologically bound to polyclonal antibodies adsorbed to a solid phase and then, after covalent immobilization with glutaraldehyde, is released from the antibody paratope by NaOH. The peptide linked to the solid phase is further quantified with a tracer consisting of the same antibodies purified by affinity chromatography and coupled to acetylcholinesterase. This assay has a detection limit of 10 pg/ml and is therefore five times more sensitive than competitive enzyme immunoassay using the same antibodies and BN 52080 coupled to acetylcholinesterase as tracer. The assay is specific and allows direct measurement of peptide in human plasma after subcutaneous or intravenous administration of 200 micrograms of BN 52080 to volunteers.

Pharmacokinetic, metabolic, and antidiarrheal properties of (D and L) heptapeptides of sorbin in rodent.

The C-terminal heptapeptide-amide (C7-sorbin) is the minimal biologically active fragment of sorbin inducing an increase in intestinal hydroelectrolytic absorption. An analogue (D7-sorbin), characterized by the replacement of the ultimate C-terminal amino acid L-alanine-amide by D-alanine-amide, was synthetized. For pharmacokinetic studies, D7-sorbin and C7-sorbin were tritium labeled. After IV injection, clearances were 10.6 and 30.2 ml-1 for D7-sorbin and C7-sorbin, respectively, and MRT were 34 and 18 min. After SC administration, Cmax attained 0.41% and 0.12% of the dose/ml, respectively. The IP route showed a 45-min delay before Cmax and a 100% bioavailability for both peptides. D7-sorbin was principally excreted in urine, as shown by balance study, and in part in intact form, as controlled by mass spectrometry. D7-sorbin induced a significant decrease of the VIP-induced ileal secretion, previously observed with C7-sorbin. The change of L-Ala to D-Ala increased the stability of the synthetic C-terminal peptide of sorbin whereas its biological activity, bioavailability, and route of elimination were unchanged.

Effect of cicletanine on overpacing-induced ST-segment elevation in conscious rabbits. A comparison with verapamil.

We compared the effects of cicletanine (10 mg/kg i.v.) and verapamil (0.1 mg/kg i.v.) on heart rate, ventricular effective refractory period, systolic and diastolic arterial blood pressure and overpacing-induced ST-segment elevation detected by right ventricular intracavital electrogram in conscious rabbits. Cicletanine significantly reduced overpacing-induced ST-segment elevation, which is an indicator of myocardial ischemia, and heart rate, but did not influence blood pressure and ventricular effective refractory period. Verapamil did not significantly influence ventricular effective refractory period, blood pressure or heart rate, but reduced the ST-segment elevation induced by frequency loading. These results suggest that acute treatment with cicletanine induces an anti-ischemic effect in the overpaced heart of conscious rabbits.

Cicletanine sulfate: inhibition of anion transport systems and natriuretic activity.

In contrast with cicletanine, its urinary sulfoconjugate metabolite (cicletanine sulfate) was active on membrane ion transport in human red blood cells. Cicletanine sulfate was a more potent inhibitor of the Na+ dependent [Cl-/HCO3-] exchanger (IC50 = 9 +/- 3 x 10(-5) mol/l; mean +/- SD of 4 experiments) than cicletanine (IC50 = 10(-3) mol/l). This inhibitory potency was intermediate between that of xipamide (IC50 = 2 x 10(-5) mol/l) and that of furosemide (IC50 = 2 x 10(-4) mol/l). Moreover, cicletanine sulfate exhibited modest inhibitory potency against the [Na+,K+,Cl-]-cotransport system (IC50 = 1 +/- 0.3 x 10(-3) mol/l; mean +/- SD of 4 experiments) and poor inhibitory activity against the [K+,Cl-]-cotransport system. Cicletanine sulfate was unable to modify the activity of Cl(-)-independent membrane carriers (Na+:H+ exchanger, Ca2+ pump, Na+:Li+ countertransport system and Na+,K+ pump). Following renal intraarterial administration in rats, cicletanine sulfate and not cicletanine, exhibited salidiuretic activity. In conclusion, the urinary sulfo-conjugate of cicletanine is an active anion transport inhibitor and natriuretic metabolite. In fact, this metabolite may be responsible for the salidiuretic action of cicletanine.

Zaprinast, cicletanine, and verapamil attenuate overdrive pacing-induced myocardial ischemia in conscious rabbits.

In conscious rabbits equipped with right ventricular electrode and left ventricular polyethylene catheters, zaprinast and cicletanine, inhibitors of phosphodiesterase (PDE) V and PDEs I and V, respectively, as well as verapamil, a Ca2+ channel blocker, decreased intracavital ST-segment elevation induced by ventricular overdrive pacing (VOP). Zaprinast and cicletanine attenuated VOP-induced QT reduction and increase in left ventricular end-diastolic pressure (LVEDP), whereas verapamil increased LVEDP. These results suggest that inhibition of cGMP-PDEs can protect heart against ischemia.

Cromakalim and cicletanine against pacing-induced myocardial ischemia in conscious rabbits.

Myocardial ischemia assessed by intracavital ST-segment elevation, shortening of ventricular effective refractory period (VERP), and increase in left ventricular end-diastolic pressure (LVEDP) was provoked by ventricular overdrive pacing (VOP) in conscious rabbits. Cromakalim (10 micrograms/kg), an ATP-sensitive K+ channel opener, and cicletanine (30 mg/kg), a cGMP-phosphodiesterase inhibitor, reduced VOP-induced ST-segment elevation and LVEDP-increase. Under resting conditions, cromakalim lowered blood pressure, increased heart rate (HR), and shortened VERP, whereas cicletanine decreased HR, prolonged VERP without changing blood pressure. Co-administration of cromakalim and cicletanine additively reduced VOP-induced ST-segment elevation, shortening of VERP, and LVEDP-increase. Cicletanine did not change cromakalim-induced hypotension but abolished reflexogenic tachycardia. This suggests that VERP shortening is not a prerequisite for the anti-ischemic effect of cromakalim, and the combination of these drugs may afford a potent and safe anti-ischemic effect without affecting hypotension induced cromakalim.

Effects of cicletanine on vasoactive systems in conscious sinoaortic-denervated dogs.

The present study investigates the antihypertensive action of cicletanine, a new antihypertensive compound with diuretic properties (or placebo), on vasopressor (catecholamines, renin-aldosterone) as well as vasodepressor (prostaglandins, kallikrein-kinin) systems in conscious chronic sinoaortic denervated (SAD) dogs. Cicletanine (10 mg/kg twice a day, per os, for one month) lowered blood pressure and heart rate. The antihypertensive action does not involve an effect on sympathetic tone (since plasma catecholamine levels were unmodified) or on plasma aldosterone levels. By contrast, urinary 6 keto PGF1 or PGE2 levels and kallikrein activity were enhanced. This result indicates that the antihypertensive effect of cicletanine is associated with a stimulation of potential vasodepressor systems (such as prostaglandins or kinins).

Cicletanine attenuates overdrive pacing-induced global myocardial ischemia in rabbits: possible role of cardiac cyclic nucleotides.

BACKGROUND: This study examined whether cicletanine, an antihypertensive drug with cGMP phosphodiesterase inhibitory effect, could alleviate ventricular overdrive pacing-induced myocardial ischemia in chronically instrumented rabbits. METHODS: An electrode-catheter implanted into the right ventricle was used for pacing (500 bpm over 5 min) and for measuring intracavital ST-segment elevation and ventricular effective refractory period (VERP). PQ and QT intervals were measured in the chest-lead ECG, and dP/dtmax as well as left ventricular end-diastolic pressure (LVEDP) were recorded through a left intraventricular catheter. In separate groups, mean arterial blood pressure (MABP) was monitored from the right carotid artery. Experiments were performed on conscious rabbits after a week of convalescence. In anesthetized, open-chest rabbits, samples were taken from the left ventricle before and after drug treatment and/or overdrive pacing for determination of cGMP and cAMP contents by radioimmunoassay. RESULTS: Intravenous cicletanine, 30 mg/kg body weight, did not change resting MABP, dP/dtmax, and LVEDP, but it did reduce heart rate and prolonged PQ and QT intervals and VERP. Overdrive pacing produced intracavital ST-segment elevation, increased LVEDP, and decreased dP/dtmax and MABP. Cicletanine administered 15 minutes before pacing significantly attenuated ST-segment elevation, increased LVEDP, and decreased dP/dtmax and MABP. In anesthetized animals, cicletanine itself slightly increased cardiac cGMP and cAMP contents. Overdrive pacing moderately increased cGMP and profoundly elevated cAMP, and in overpaced rabbits, cicletanine further increased cGMO and markedly attenuated cAMP content increased by overdrive pacing. CONCLUSIONS: These results suggest that in correlation with alterations of cardiac cycle nucleotide contents, cicletanine protects the heart against pacing-induced myocardial ischemia.

Alpha 2-adrenoceptor changes during cerebral ageing. The effect of Ginkgo biloba extract.

[3H]Rauwolscine binding to alpha 2-adrenoceptors in cerebral cortex and hippocampus membranes of young (4 months) and aged (24 months) Wistar rats has been investigated. In aged rats, Bmax values of [3H]rauwolscine binding were significantly reduced (25-32%) in the cerebral cortex and hippocampus, as compared with the number of alpha 2-adrenoceptors found in young rats. Chronic treatment with Ginkgo biloba extract did not alter [3H]rauwolscine binding in the hippocampus of young rats, but significantly increased (28%) the [3H]rauwolscine binding density in aged rats. These data confirm the previously described age-related noradrenergic alteration and suggest that noradrenergic activity in aged rats is more susceptible to Ginkgo biloba extract treatment.

Effect of BN 50727 on pathological findings and tissue platelet activating factor levels during ileal ischemia in newborn piglets.

The role of platelet activating factor (PAF), a potent ulcerogen mediator in the digestive tract, is thought to be important in the genesis of necrotizing enterocolitis. The aim of this study was to evaluate the role of PAF in the perpetuation and aggravation of gastrointestinal damage resulting from limited ischemia in the 2-day-old piglet using a natural PAF antagonist (BN 50727). Animals were separated into six groups: U4, controls; S, sham operated animals undergoing laparotomy; I4 and I9, ligation of the mesenteric vessels in the last ileal loop; IT4 and IT9, same procedure together with treatment with BN 50727 (50 mg/kg) orally before and after surgery and intraperitoneally during surgery. Animals were killed at day 4 in groups U4, S, I4 and IT4 and at day 9 in groups I9 and IT9, with histological studies and mediator measurements taken. Macroscopic and histological lesions of intestinal wall in groups I4, I9, IT4 and IT9 were similar to those of human neonatal necrotizing enterocolitis and did not vary according to the absence or the presence of BN 50727 treatment (P = .7, I4 v IT4 and P = .9, I9 v IT9). Peritoneal bands were significantly reduced in treated groups IT4 and IT9 as compared with untreated ones I4 and I9 (P = .003). Mucosal PAF levels in the terminal ileum were higher in group I4 than in groups U4 or I9. In the upper loop, mucosal PAF levels were comparable in all groups. An increase in stool PAF levels was observed only in group I9 (26.4 ng/g v 4.7 ng/g, I9 v U4 + S, P < .05), whereas values comparable to those observed in controls were detected in other groups (I4, 7.2 ng/g; IT4, 4.5 ng/g; IT9, 6.8 ng/g). Tumor necrosis factor alpha (TNF alpha) measurements did not exhibit any difference between groups. Using a PAF antagonist, the role of PAF in the aggravation of intestinal damage after ischemia was not remarkable because treatment did not induce any modifications of parietal intestinal lesions. PAF antagonists appeared to reduce significantly the local peritoneal consequences of local inflammation.

Efficacy and tolerance of cicletanine, a new antihypertensive agent: overview of 1226 treated patients.

The data gathered from 1226 patients for 20 controlled therapeutic studies performed during the phase-III development of cicletanine, a new antihypertensive agent, were pooled in a computerized database. An extensive statistical analysis of these data collected over 1-2 years was performed to give a clear interpretation of long-term efficacy and tolerance of this drug. In mild to moderate hypertension, the dose-response relationship observed after one month of treatment on diastolic (DBP) and systolic (SBP) blood pressure disappeared during the third month. After a 3-month treatment in monotherapy with the recommended dosage (50-100 mg/day) we observed a mean decrease of 29.7 +/- 17.8 mmHg for SBP and 23.3 +/- 13.2 mmHg for DBP. At this stage 70.9% of patients were stabilized (SBP less than 160 mmHg and DBP less than 95 mmHg) with cicletanine. After this initial regular decrease of blood pressure values, an additional decrease of several mmHg was observed during the 24 months of treatment, thus significantly augmenting the number of stabilized patients. No significant difference in efficacy was observed in adult and elderly (65 to 95 years) patients. The clinical tolerance was very good, only a few slight and transitory side-effects have been reported. Biological tolerance was also very good. Depending on the dosage used, only a slight and transitory variation in sodium and potassium levels was observed. Glucose, creatinine and lipids either remained stable or were improved during treatment. This analysis demonstrates the beneficial effect and the good tolerance of cicletanine (50-100 mg/day) in the treatment of hypertension, which can be explained by its special mode of action.

Haemodynamic effects of an antihypertensive diuretic substance on the forearm circulation of patients with essential hypertension.

Vascular resistance, arterial compliance and venous tone of the forearm were determined using plethysmographic and Doppler techniques in patients with sustained essential hypertension before and after administration of a new antihypertensive agent with low diuretic effect, cicletanine. After 1 week of treatment, no significant change in the haemodynamic parameters was observed. After 3 months' treatment, blood pressure and forearm vascular resistance significantly decreased, but arterial diameter and forearm venous tone did not change. The study suggested that the antihypertensive effect of cicletanine involved a pharmacological action of the drug on the arterial smooth muscle of both small and large arteries, independently of the blood pressure reduction.

[Cicletanine administered with other antihypertensive agents]. / Etude du ciclétanine administré en association avec d'autres antihypertenseurs.

The antihypertensive effectiveness and the clinical and biochemical safety of cicletanine were evaluated in 84 patients (28 women, 56 men) presenting with permanent essential hypertension without severe cardiovascular complications. The hypertension was insufficiently controlled by a beta-blocker, a centrally acting antihypertensive drug or nifedipine. After 3 months of treatment during which cicletanine was added to each of these three classes of drugs, there was a significant fall of systolic arterial pressure (-18 mmHg with beta-blockers, -17 mmHg with central agents and -26 mmHg with nifedipine) and diastolic arterial pressure (-22, -21 and -28 mmHg respectively), resulting in normalization of blood pressure (less than 160/95 mmHg) in 63%, 43% and 50% respectively of patients in each therapeutic group. The fall of blood pressure was accompanied by a significant decrease of functional symptoms (headache, palpitations, dizziness); in the nifedipine group, the addition of cicletanine resulted in complete regression of anginal attacks. The therapeutic combinations were well tolerated; only two patients were excluded from the study for undesirable effects unascribable to cicletanine. Otherwise, the side-effects observed were minor. The biochemical values measured did not significantly vary, and the variations noted were of small amplitude.

[Comparative study of 2 dosages of a new antihypertensive agent, cicletanine, in elderly subjects]. / Etude comparative de deux posologies d'un nouvel antihypertenseur, le ciclétanine, chez le sujet âgé.

Cicletanine chlorhydrate (C), a furopyridine derivative, is a new antihypertensive drug that acts mainly by enhancing endogenous prostacyclin release. It has been shown to induce a significant, progressive reduction in systolic and diastolic blood pressure in patients over 60 years of age at a daily dose of 150 mg in a placebo-controlled efficacy trial. As concurrent studies in adult hypertensive patients demonstrated an antihypertensive effect at even lower doses, we further compared the antihypertensive efficacy and tolerance of 50 mg vs 100 mg daily dose of C in elderly hypertensive patients in order to determine the lowest active posology. A prospective, double-blind randomized trial included 72 patients (56 female, 16 male) aged 65 years or more (mean age +/- 1 SD: 80.3 +/- 5.9 years, range 65-90) with moderate, essential hypertension, and normal-for-age renal function whose diastolic BP was greater than 95 mmHg and/or systolic BP was greater than 160 mmHg after 15 days of a single-blind placebo period. They were randomly allocated to either 50 mg (group I, 36 patients) or 100 mg (group II, 36 patients) C given in a single morning dose for 3 months with monthly surveillance. Of them, 60 achieved satisfactory BP control with C as monotherapy and completed full follow-up.(ABSTRACT TRUNCATED AT 250 WORDS)

[Antihypertensive effectiveness and tolerance of cicletanine. Results obtained with monotherapy in a large population]. / Efficacité antihypertensive et tolérance du ciclétanine. Résultats obtenus en monothérapie sur une large population.

A multicentre open study to which 229 investigators participated was carried out to demonstrate the safety of cicletanine, a new therapeutic agent, in routine clinical use. Cicletanine was administered alone for three months and normalized blood pressure (less than 160/95 mmHg) in 63 p. 100 of the 1,238 hypertensive patients who entered the study. There was a significant fall of systolic arterial pressure from 178.4 +/- 14.8 to 151.8 +/- 14.2 mmHg and a similar fall of diastolic arterial pressure from 104.0 +/- 6.7 to 86.3 +/- 6.2 mmHg. The reduction of BP values was accompanied by a significant decrease of differential BP (SBP-DBP) from 72.5 to 65.8 mmHg. The initial dosage (50 mg/day) was doubled in only one-third of the patients. The mean daily dose was 66 mg. This antihypertensive effect was paralleled by a significant and major improvement of signs (dyspnoea, oedema of the lower limbs) and symptoms (mainly dizziness, headache, visual and auditory disorders, asthenia) which existed at inclusion. A modest, but significant, reduction of heart rate from 76.7 to 73.9 beats/mn was also noted. Cicletanine produced no toxic or severe adverse events. Clinical side-effects consisted of pruritus, fatigue, headache, vertigo, lower limb oedema and gastrointestinal disorders. These effects were mild and non-specific (doubtful drug imputability); each of them occurred with an incidence ranging from 4.0 to 1.0 p. 100. They were responsible for the withdrawal of about 30 patients (2.4 p. 100). No significant alteration of biochemical or haematological values was recorded.(ABSTRACT TRUNCATED AT 250 WORDS)

[Anatomic aspects of Prinzmetal's angina: apropos of an anatomo-clinical case]. / Les aspects anatomiques de l'Angor de Prinzmétal: à propos dune observation anatomoclinique

Report of one case of Prinzmetal variant of angina pectoris with a typical clinical and electrocardiographic picture in a man aged 87. Severe arrhythmias resulted in death of the patient. On autopsy a moderate narrowing of the anterior interventricular artery was demonstrated. In that relation, a review of the literature on the anatomical lesions and coronary arteriographic data of Prinzmetal angina was performed. It showed that in some cases Prinzmetal angina could be observed while the coronary artery lesions were very moderate. The pathogenesis of these facts was discussed.

[Antihypertensive effectiveness and tolerance of cicletanine. Results obtained with bitherapy]. / Efficacité antihypertensive et tolérance du ciclétanine. Résultats obtenus en bithérapie.

In a multicentre open trial involving 229 investigators, cicletanine, a new antihypertensive agent, was administered orally in doses of 50 to 100 mg/day either alone (1,238 patients) or combined with another drug (430 patients). In this second group of patients with essential hypertension whose BP had not been normalized by a beta-blocker (n = 157), a calcium inhibitor (n = 67), an angiotensin-converting enzyme inhibitor (n = 134) or an alpha-blocker (n = 7), cicletanine normalized BP (less than 160/95 mmHg) in 48.8% of the patients and significantly lowered BP values which fell from 177.7 +/- 15.9/103.3 +/- 6.3 mmHg to 157.2 +/- 17.6/88.8 +/- 8.7 mmHg. The addition of cicletanine to treatments with beta-blockers, calcium inhibitors and angiotensin-converting enzyme inhibitors normalized BP in 48%, 52% and 47% of patients respectively. A significant reduction of symptoms was noted, notably as regards headache, dizziness, palpitations, lower limb oedema, asthenia, auditory disorders and dyspnoea. The side-effects reported (headache, dizziness, gastralgia, nausea, pruritus) were minor and non-specific; they accounted for the withdrawal of only 8 patients. The only significant, though moderate, biochemical variations observed were decreases in natremia and cholesterolaemia unconfirmed by qualitative analysis. Altogether, cicletanine proved to be effective and well tolerated when administered in combination with other antihypertensive drugs belonging to three main therapeutic classes.