Plasma atrial natriuretic peptide (ANP) fragments proANP (1-30) and proANP (31-67) measurements in chronic heart failure: a useful index for heart transplantation?

The family of the atrial natriuretic peptides, proANP fragments and the active alphaANP, is strongly related to heart disease. The aim was to study in CHF subjects the relation of mdANP and NtANP with brain natriuretic peptide (BNP) and with other traditional medical parameters. Sixteen CHF patients (aged 51.9+/-13.7 years) and 16 healthy subjects age matched (50.8+/-5.9 years) were selected. Both NtANP and mdANP were higher in CHF patients than in healthy subjects (1436+/-288 vs. 288+/-22 pmol/l p<0.001 and 2305+/-383 vs. 423+/-65 pmol/l p<0.0001, respectively). BNP in CHF patients was 28.0+/-9 pmol/l (reference values 1.7+/-1.8 pmol/l). Both NtANP and mdANP demonstrated positive correlation with BNP, p<0.0001 and with left atrial end-systolic volume, p<0.05. BNP correlated with left ventricular mass, p<0.03. In conclusion, plasma NtANP and mdANP analyses are useful laboratory markers in CHF patient investigation and follow up. In particular, they could be employed as non-invasive parameters to follow up worsening of systolic dysfunction until heart transplantation is required.

Pharmacological characterization of a new Ca(2+) sensitizer.

The benzimidazole molecule was modified to synthesize a Ca(2+) sensitizer devoid of additional effects associated with Ca(2+) overload. Newly synthesized compounds, termed 1, 2, 3, 4, and 5, were evaluated in spontaneously beating and electrically driven atria from reserpine-treated guinea pigs. Compound 3 resulted as the most effective positive inotropic agent, and experiments were performed to study its mechanism of action. In spontaneously beating atria, the inotropic effect of 3 was concentration-dependent (3.0 microM-0.3 mM). Compound 3 was more potent and more active than the structurally related Ca(2+) sensitizers sulmazole and caffeine, but unlike them it did not increase the heart rate. In electrically driven atria, the inotropic activity of 3 was well preserved and it was not inhibited by propranolol, prazosin, ranitidine, pyrilamine, carbachol, adenosine deaminase, or ruthenium red. At high concentrations (0.1-1.0 mM) 3 inhibited phosphodiesterase-III, whereas it did not affect Na(+)/K(+)-ATPase, sarcolemmal Ca(2+)-ATPase, Na(+)/Ca(2+) exchange carrier, or sarcoplasmic reticulum Ca(2+) pump activities of guinea pig heart. In skinned fibers obtained from guinea pig papillary muscle and skeletal soleus muscle, compound 3 (0.1 mM, 1 mM) shifted the pCa/tension relation curve to the left, with no effect on maximal tension and no signs of toxicity. Compound 3 did not influence the basal or raised tone of guinea pig isolated aorta rings, whose cells do not contain the contractile protein troponin. The present results indicate that the inotropic effect of compound 3 seems to be primarily sustained by sensitization of the contractile proteins to Ca(2+).

Endothelium is required in the vascular spasm induced by tetraethylammonium and endothelin-1 in guinea-pig aorta.

1. To investigate the role of endothelium in vascular spasm, we studied the influence of endothelin-1 (ET-1) on the contracting and spasmogenic effect of the K+-channel blocker, tetraethylammonium (TEA), in aorta rings of reserpine-treated guinea-pigs, perfused with either control (5.5 mM) or elevated (50 mM) glucose concentration. 2. Endothelium-dependent relaxation induced by acetylcholine was lost in rings contracted by noradrenaline in the presence of elevated glucose. In control medium, TEA (1-20 mM) induced a sustained tonic contraction, followed by a phasic spasm, characterized by rhythmic contractions. Elevated glucose, ET-1 (3 nM), or both, reduced the EC50 of TEA-induced tonic contraction, without modifying the maximum contractile effect. 3. In control medium, ET-1 reduced the time before TEA-induced spasm and increased the rate of rhythmic contractions. TEA-induced spasm was abolished by elevated glucose, and restored by ET-1. The spasm induced by TEA and ET-1 was amplified by the ETA antagonist, EMD94246, and suppressed by the ET(A)-ET(B) antagonist, bosentan. In endothelium-denuded vessels incubated with high glucose and ET-1, TEA evoked only a tonic contraction. 4. In control medium, L-NAME (N(G)-nitro-L-arginine methyl ester) abolished TEA-induced rhythmic contractions. L-arginine, but not D-arginine, prevented the effect of L-NAME. In the presence of elevated glucose and ET-1, TEA-induced spasm was not affected by L-NAME, whereas verapamil, indomethacin, metyrapone, glybenclamide or apamin abolished the phasic spasm, unmasking the tonic contracture. 5. In conclusion, endothelium plays a regulatory role in the genesis and maintenance of TEA-induced rhythmic contractions, through the release endothelium derived relaxing factor and vasodilating eicosanoids.

Early reduction in plasma norepinephrine during beta-blocking therapy with metoprolol in chronic heart failure.

BACKGROUND: The possible role exerted by modulation of sympathetic outflow in the clinical effects of beta-blockade in chronic heart failure was tested during short- and long-term treatment. METHODS AND RESULTS: Oral metoprolol (30-150 mg/day) was added to conventional therapy in 14 patients with idiopathic dilated cardiomyopathy, left ventricular ejection fraction (LVEF) of <0.45, and New York Heart Association class II or III. Norepinephrine plasma levels, which are an index of sympathetic activation, decreased by 27.57 +/- 18.03% after 1 month (P < .005), but returned to pretreatment levels after 6 months. LVEF increased by 7.7 +/- 6.0 ejection fraction units after 6 months (P < .005 vs baseline and P < .05 vs 1 month). Long-term beta-blockade resulted in nonsignificant improvements in functional class, symptom score, and oxygen consumption at peak exercise. After 1 month, the reduction in plasma norepinephrine levels and the changes in LVEF were inversely correlated (P < .01). No other correlation emerged during short- or long-term treatment. CONCLUSION: In conclusion, the reduction in plasma norepinephrine levels during short-term beta-blockade was not proportional to the clinical benefits and may have been attributed to the direct inhibition of sympathetic outflow. The early reduction in circulating norepinephrine levels may decrease cardiac performance through withdrawal of sympathetic support when the favorable effects of beta-blockade have not had time to occur. The role that sympathetic modulation may exert in the long-term clinical benefits of metoprolol deserves further investigation.

Impairment of endothelium-dependent but not of endothelium-independent dilatation in guinea-pig aorta rings incubated in the presence of elevated glucose.

1. Purine compounds such as ATP and adenosine, respectively endothelium-dependent and- independent vasodilators, are largely involved in the control of vascular tone and vascular reactivity to contracting stimuli. We investigated the relaxing activity of ATP and adenosine in guinea-pig aorta rings exposed for 6 h to elevated glucose concentration (50 mM), in order to mimic hyperglycaemic conditions. Guinea-pigs were reserpine-treated (2 mg kg-1, i.p., 48 and 24 h before death). 2. Rings of aortae incubated in 50 mM glucose, contracted submaximally by 1 microM noradrenaline, lost endothelium-dependent relaxation in response to acetylcholine (10 nM to 10 microM). Aortae incubated with 50 mM mannose, as a hyperosmotic control, relaxed to acetylcholine normally. Rings of aortae incubated in 50 mM glucose, contracted submaximally by 3 mM 4-aminopyridine, lost endothelium-dependent relaxation in response to ATP (30 microM) whereas endothelium-independent relaxation in response to adenosine (0.3 mM) was well preserved. 4. The relaxation induced by A23187 or sodium nitroprusside (10 nM to 0.1 microM) did not differ between rings exposed to control (5.5 mM) or elevated glucose (50 mM) and contracted submaximally by 3 mM 4-aminopyridine. 5. When incubated with aortic tissue in the presence of elevated glucose, the cyclo-oxygenase inhibitors, indomethacin (10 microM) and mefenamic acid (30 microM), or the scavenger of superoxide anions, superoxide dismutase (150 u ml-1), prevented the impairment of ATP-mediated relaxation. 6. The present results indicate that endothelium-dependent, receptor-induced relaxation in response to acetylcholine and ATP is impaired in guinea-pig aorta rings exposed to elevated glucose. The endothelial dysfunction caused by glucose might be located at a step between receptor activation and intracellular calcium increase, and might be related to an increased metabolism of arachidonic acid coupled to an increased production, or to a reduced inactivation of superoxide anions.

New inotropic agents: milrinone analogs.

1. Two new milrinone analogs, 3-acetyl-6-phenyl-2(1H)-pyridone (SF 348) and 3-acetyl-7-methyl-7,8-dihydro-2,5(1H, 6H) quinolinone (SF 349), increase the contractile activity of spontaneously beating and electrically driven atria isolated from reserpine-treated guinea-pigs. 2. Propranolol 0.1 microM drastically inhibits the contractile effect of SF 348, whereas that of SF 349 is unaffected. Preincubation of the atria with adenosine-deaminase suppresses the cardiac activity of SF 349, but does not affect that of SF 348. 3. SF 349 competitively antagonizes the negative inotropic effect induced by N6-(R-phenylisopropyl)-adenosine (R-PIA) and displaces N6-cyclohexyl[3H]-adenosine (3H-CHA) from its binding sites to A1 receptors in the guinea-pig heart. 4. The positive inotropic effect of SF 348 is largely sustained by activation of beta-adrenoceptors, whereas SF 349 acts by displacing endogenous adenosine from its inhibitory (A1) receptors in the atria.

Characteristics of chief complaints of patients with temporomandibular disorders in a Brazilian population.

A retrospective survey of 894 patients with temporomandibular disorders was conducted in order to analyse the characteristics of chief complaints. The patients presented complaints of pain (82.1%), functional disturbance (12.3%), articular sounds (5.0%) and swelling (0.6%). Unilateral occurrence (66.5%) was more frequent than bilateral. The most frequent location of pain was the temporomandibular joint (TMJ) (82.1%) followed by ear (10.8%), face (2.3%), head (2.3%), mandible (1.0%), neck (0.9%), temporal (0.4%) and frontal (0.1%) areas. Pain in the TMJ occurred in isolation (87.9%) or associated to other locations. The most frequent functional disturbance was limitation of jaw opening (32.1%).

Characteristics of cheif complaints of patients with temporomandibular disorders in a brazilian population / Caracteristicas das reclamações dos pacientes com desordens temporomandibulares da população brasileira

A retrospective survey of 894 patients with temporomandibular disorders was conducted in order to analyse the characteristics of chief complaints. The patients presented complaints of pain (82.1 percent), functional disturbance (12.3 percent) articular sounts (5.0 percent) and swelling (0.6 percent). Unilateral occurrence (66.5 percent) was more frequent than bilateral. The most frequent location of pain was the temporomandibular joint (TMJ) (82.1 percent) followed by ear (10.8 percent), face (2.3 percent), head (2.3 percent), mandible (1.0 percent), nech (0.9 percent), temporal (0,4 percent) and frontal (0.1 percent) areas. Pain in the TMJ occured in isolation (87.9 percent) or associated to other locations. The most frequent functional disturbance was limitation of jaw opening (32.1 percent)

Synthesis and cardiotonic activity of novel pyrimidine derivatives: crystallographic and quantum chemical studies.

The synthesis of ethyl or methyl 4-substituted or unsubstituted 2-(dimethylamino)-5-pyrimidinecarboxylates 10-20, which is mainly carried out by reaction of ethyl or methyl 2-[(dimethylamino)methylene]-3-oxoalkanoates with 1,1-dimethylguanidine, is described. The above esters were hydrolyzed to the relative carboxylic acids 21-30, which were decarboxylated to the corresponding 2,4-disubstituted pyrimidines 31-40. All the new synthesized pyrimidines were evaluated in spontaneously beating and electrically driven atria from reserpine-treated guinea pigs. Their effects were compared to those induced by milrinone in both atria preparations. Compound 28 (4-benzyl-2-(dimethylamino)-5-pyrimidinecarboxylic acid) was the most effective positive inotropic agent, while the corresponding methyl ester 17 reduced both the contractile force and the frequency of guinea pig atria. An antagonism toward the negative influence exerted by endogenous adenosine on the heart seems to be involved in the contractile activity of compound 28. By contrast, compound 17 might be partial agonist at the purinergic inhibitory (A1) receptor. X-ray analysis carried out on 17 and 28 and molecular modeling investigations extended also to related derivatives allowed a possible rationalization between structure and inotropic activity for this series of compounds.

[Hemodynamics and clinical data in chronic coronary disease with severe left ventricular systolic dysfunction]. / Emodinamica centrale e dati clinici nella coronaropatia cronica con grave disfunzione sistolica ventricolare sinistra.

To elucidate how symptoms and signs of chronic heart failure are related to the filling pressure and cardiac output at rest, 58 patients (55 males, 3 females, mean age 57 +/- 9 years, range 30-75) with left ventricular ejection fraction (LVEF) < or = 30% and a lesion > or = 50% on a major coronary branch have been selected from patients submitted in 1985-1993 to a complete right and left cardiac catheterization including ventriculography and coronary angiography. Patients with recent myocardial infarction (MI), unstable angina, associated heart diseases or recent changes in body weight and in diuretic therapy were excluded. Clinical data were obtained at cardiac catheterization time from history, physical examination, chest X-ray and ECG. Patients with angina as limiting symptom were excluded from NYHA functional classification. Pulmonary venous congestion (PVC) was defined on X-ray as: absent, venous redistribution, interstitial pulmonary edema (IPE). Mean pulmonary capillary wedge pressure (PCWP) was recorded under fluoroscopy and cardiac index was measured by the Fick method. On the whole group, 96% of patients had had one or more MI (on ECG necrosis was anterior in 58%, inferior in 9%, anterior and inferior in 26%), 69% were in NYHA functional class III or IV, 54% had IPE and 45% had mitral regurgitation. 71% were under treatment with digitalis, 74% with diuretics and 39% with ACE-inhibitors. PCWP was correlated with LVEDV (r = 0.34; p < 0.001) but neither with LV mass nor with LV mass/volume ratio. It was significantly higher (p < 0.01) in patients with mild-moderate mitral regurgitation, in patients with necrosis involving both anterior and inferior walls (26 +/- 6 vs 21 +/- 8 mmHg in patients with single wall necrosis, p < 0.05) and in patients with multiple MI (26 +/- 7 vs 20 +/- 8 mmHg in patients with no or single MI, p < 0.02). Moreover, it was neither correlated with functional classification nor with PVC: of patients with PCWP > 24 mmHg, 14% were in II NYHA functional class and 21% had no PVC while of patients with PCWP < 15 mmHg, 36% were in NYHA functional class IV and 7% had IPE. Cardiac index was reduced below 2.3 l/min/m2 in 21% of patients: these patients had increased pulmonary (p < 0.0002) and systemic (p < 0.0001) vascular resistance, increased systolic (p < 0.001) and diastolic (p < 0.01) pulmonary artery pressure and reduced LVEF (p < 0.01) and right ventricular ejection fraction (p < 0.03). Furthermore, on the whole patients an inverse correlation was found between cardiac index and functional classification (r = -0.42; p < 0.01). The reliability of NYHA functional class IV, physical signs of heart failure and IPE for estimating PCWP > 24 mmHg and cardiac index < 2.3 l/min/m2 was rather limited although high specificity was shown for gallop sounds (92 and 97%) and jugular vein distension (88 and 97%). In conclusion, in coronary patients with chronic severe LV systolic dysfunction a mismatch between clinical data and central hemodynamics is not rare. The reliability of functional class, X-ray PVC and physical signs to predict central hemodynamics in fairly limited.

Chemical and pharmacological characterization of Erythrophleum lasianthum alkaloids.

Two alkaloids 1 and 2 were isolated from the seeds of Erythrophleum lasianthum. Their structures were assigned by spectroscopic and chemical means as 3 beta-hydroxynorerythrosuamine (1) and its 3-O-beta-D-glucopyranoside (2). In spontaneously beating atria, both compounds 1 and 2 showed a marked and concentration-dependent positive inotropic activity and a weak negative chronotropic activity. The positive inotropic effect induced by 1 and 2 was not modified by propranolol, prazosin, carbachol, and ranitidine plus pyrilamine. Both 1 and 2 were very active in inhibiting the Na+/K(+)-ATPase isolated from bovine cardiac sarcolemmal vesicles.

Influence of beta-blockade with metoprolol on symptoms and functional capacity of patients with idiopathic dilated cardiomyopathy.

Long-term treatment with beta-adrenergic blocking drugs has been shown to induce clinical amelioration in patients with chronic heart failure. However, the efficacy of these agents has not been consistent, and the mechanisms of their beneficial effects remain to be established. The present study evaluated the influence of oral metoprolol on symptoms and exercise tolerance of patients with idiopathic dilated cardiomyopathy (3 women and 9 men, left ventricular ejection fraction < 0.45, NYHA functional class II or III). One patient did not tolerate metoprolol, whereas 11 patients terminated the study. After 6 months of beta-blocking therapy, detectable improvements of symptoms (NYHA class and questionnaire-derived symptom score) were observed in 6 patients. Six patients reported an increase in functional capacity [oxygen consumption at peak exercise (VO2p) during cardiopulmonary exercise test]. For the whole group, no significant changes in symptoms and exercise tolerance were detected. During exercise, oxygen pulse (VO2/heart rate) and VO2/RPP (VO2/heart rate/systolic pressure) were significantly increased after 6 months on metoprolol (+35, 9% and +27.1%, respectively; both p < 0.01 vs baseline). In conclusion, beta-blocking therapy was well tolerated by the majority of patients, some of which reported improvement of symptoms and functional capacity. The observed increase on oxygen pulse and Vo2/RPP suggests that beta-blockade may reduce myocardial oxygen requirements in proportion to cardiac work. An increase in the energy available to myocardial cells for synthetic and reparative processes may thus account, at least in part, for the beneficial influence of long-term beta-blockade in heart failure patients.

Pharmacological characterization of a new milrinone analogue.

In a new series of milrinone analogues (esters of 2-substituted 5-acetyl-1,6-dihydro-6-oxo-3-pyridinecarboxylic acids), ethyl 5-acetyl-1,6-dihydro-6-oxo-2-phenyl-3-pyridinecarboxylate (compound 2f) has been found to be more potent and more effective than milrinone as a positive inotropic agent while affecting only marginally the frequency rate of guinea-pig isolated atria. This finding prompted us to study the mechanism of cardiac action of compound 2f in electrically driven left atrium from reserpine-treated guinea pigs. Compound 2f induced a statistically significant increase in the contractile force at a concentration as low as 1 microM, while the minimum effective concentration of milrinone was 10 microM. The beta-blocker propranolol (0.1 microM) caused a marked inhibition of the inotropic effect of compound 2f. Adenosine deaminase (1 and 2 U/ml) inhibited significantly and in a concentration-dependent manner the increase in inotropism induced by compound 2f and the adenosine deaminase-resistant response was abolished by 0.1 microM propranolol. In the presence of 0.1 microM propranolol, compound 2f (5 to 30 microM) antagonised in competitive manner the negative inotropic effect induced by N6-(R-phenylisopropyl) adenosine (R-PIA) (0.01-1.0 microM), a stable adenosine receptor agonist. Schild regression analysis gave in fact a slope of 1.02 +/- 0.06 and the pA2 value for compound 2f was 5.41 +/- 0.28. Compound 2f also inhibited phosphodiesterase (PDE) III isolated from calf heart, this inhibition being quantitatively significant only at the highest concentrations tested (0.5 M to 1 mM).(ABSTRACT TRUNCATED AT 250 WORDS)

A pharmacological, crystallographic, and quantum chemical study of new inotropic agents.

The cardiac activity of a series of milrinone analogues, 2-substituted 3-acyl-1,6-dihydro-6-oxo-5-pyridinecarbonitriles, 1,6,3,2,11,12-hexahydro-6,3-dioxo-5-quinolinecarbonitriles, the correlated carboxylic acids, 2-substituted 3-acyl-6(1H)-pyridones, and 7,8-dihydro-2,5(1H,6H)-quinolinediones, was evaluated in spontaneously beating and in electrically driven atria from reserpine-treated guinea pigs. Their effects were compared with those induced by amrinone and milrinone in both the atria preparations. Compounds SF28 (3-acetyl-1,6-dihydro-2-methyl-6-oxo-5-pyridinecarbonitrile) and SF40 (7,8-dihydro-7-methyl-2,5(1H,6H)-quinolinedione) were the most effective positive inotropic agents. An inhibition of the negative influence exerted by endogenous adenosine on heart preparations seems to be involved in their contractile activity. SF38 (3-benzoyl-2-phenyl-6(1H)-pyridinone), on the contrary, reduced the contractile force and the frequency rate of guinea pig atria with a mechanism not related to an activation of cholinergic or purinergic inhibitory receptors on the heart. X-ray analysis carried out on the three model compounds, SF28, SF40 (positive inotropic agents), and SF38 (negative inotropic agent), and molecular modeling evidenced that the change from phenyl (SF38) to methyl (SF28) or the introduction of a side cyclic aliphatic chain (SF40) results in a variation of conformational preference and topography which may address the different molecules toward distinct receptor pockets according to the resulting inotropic effect.

[Clinical and instrumental findings in cardiac amyloidosis]. / Contributi clinici e strumentali all'amiloidosi cardiaca.

The clinical findings of 2 male patients, aged 58 and 60 years with cardiac amyloidosis are described. Congestive heart failure was present in both. Electrocardiograms were abnormal in both cases. Echocardiographic examination showed increased myocardial echogenicity and ventricular hypertrophy, pericardial effusion and decreased ventricular function. Cardiac catheterization was performed in 1 patient. Rectal biopsies were obtained from both patients; endomyocardial biopsy was executed in only 1 patient; all specimens were positive. Our data demonstrate, in agreement with the literature, that clinical features of cardiac amyloidosis are polymorphous and therefore often unidentified.

Vasodilatory activity of etozoline in rat and guinea-pig isolated aorta: study of the mechanism of action.

In isolated rings of guinea-pig aorta not responding to acetylcholine, the diuretic etozoline did not influence basal vascular tone but inhibited noradrenaline- and histamine-induced contractions. The inhibition was evident at concentrations of the diuretic (10 microM-1 mM) suitable to inhibit, in a competitive manner, the contractions evoked by a K+ channel blocker, tetraethylammonium, in the same preparation (Dorigo et al., 1989, 1990). In isolated rings of guinea-pig aorta, etozoline, at very low concentrations (1 nM-0.1 microM), inhibited also serotinin-induced contractions. The contractile effect of serotonin was abolished by nifedipine associated with 2-nitro-4-carboxyphenyl N,N-diphenyl-carbamate (an inhibitor of phospholipase C) or with etozoline, thus suggesting that the diuretic, besides inhibiting extracellular Ca++ uptake, also prevents intracellular Ca++ mobilization mediated by inositol triphosphate. In isolated rings of rat aorta responding to acetylcholine, etozoline did not influence basal vascular tone either in the absence or in the presence of superoxide-dismutase. In the same preparation, the diuretic inhibited vascular contractions induced by the three spasmogenic agents used, i.e. noradrenaline, histamine and serotonin. This inhibition occurred at concentrations of etozoline ranging from 10 microM to 1 mM and was uninfluenced by indomethacin (10 microMs). In isolated rings of rat aorta, the contractile effect of noradrenaline was not influenced by the addition of either 100 microM pyrogallol, or 10 microM methylene blue or 100 U/ml superoxide-dismutase, while the contractile responses to histamine and to serotonin were potentiated by pyrogallol and by methylene blue and reduced by superoxide-dismutase. This indicates that, in rat aorta, noradrenaline evokes only a direct contractile response, whereas both serotonin and histamine have a double effect: direct contraction of vascular smooth muscle and release of a relaxing factor from the endothelium. The inhibitory activity of etozoline towards serotonin- and histamine-induced contractions was reduced by pyrogallol and by methylene blue, whereas it was potentiated by superoxide-dismutase. The ability of etozoline to reverse the noradrenaline-induced contraction was unaffected by pyrogallol, methylene blue or superoxide-dismutase. These results emphasize the spasmolytic activity of etozoline, which seems to involve only the muscular component of rat and guinea-pig aorta.

An analysis of the mechanism of the inotropic action of some milrinone analogues in guinea-pig isolated atria.

1. It has been reported previously that the milrinone analogues, ethyl 5-cyano-1,6-dihydro-2-methyl-6-oxo-3 pyridine carboxylate (I) and ethyl 5-cyano-1,6-dihydro-2-ethyl-6-oxo-3 pyridine carboxylate (II) exert a positive inotropic effect (EC50 = 15.6 +/- 0.2 microM and 40.3 +/- 0.1 microM) both on spontaneously beating and on electrically driven atria from reserpine-treated guinea-pigs. In the present study the mechanism of the inotropic action of these two agents was investigated. 2. In electrically driven left atrium from reserpine-treated guinea-pigs the EC50 values for inotropic activity for compounds (I) and (II) corresponded to that of milrinone (EC50 = 25 +/- 0.1 microM) but compound (I) induced a greater maximum effect. This corresponded to a percentage increase in developed tension over control of 63 +/- 0.3 whereas the maximum inotropic effect of milrinone was 48 +/- 0.3 and that of compound (II) was 47 +/- 0.2. 3. The inotropic activity of compounds (I) and (II) (10-100 microM) was resistant to propranolol (0.1 microM), thus excluding the involvement of beta-adrenoceptors. 4. Since the inotropism induced by compounds (I) and (II) was not reduced by carbachol (1 nM-0.5 microM), an action involving changes in adenosine 3':5'-cyclic monophosphate (cyclic AMP) can be excluded. 5. The inotropic action of compounds (I) and (II) was blocked selectively by 8-phenyltheophyline (10 microM) or adenosine deaminase (2 u ml-1). 6. Both (I) and (II) inhibited, in an apparently competitive manner, the negative inotropic effect induced by N6-(L-phenylisopropyl) adenosine (L-PIA), a stable adenosine agonist. The pA2 values for (I) and (II) were 4.79 and 4.36, respectively.7. In rat brain compounds (I) and (II) inhibited the specific binding of N6-cyclohexyl[3H]-adenosine- ([3H]-CHA) with an IC50 of 0.18 + 0.01 mM and 0.25 + 0.02 mm, respectively, which were similar to their IC50 values for blocking the PIA-induced negative inotropic effect and which are also in the range of concentrations that are effective in inducing positive inotropism in guinea-pig atria.8. The results from the present study suggest that antagonism of endogenous purines causes positive inotropism without affecting intracellular cyclic AMP levels.

Comparison between the cardiac effects induced by muzolimine and furosemide in guinea-pig atria.

Muzolimine (10-500 microM) induced a concentration-dependent reduction of both the contractile force and frequency in spontaneously beating atria and in electrically driven left atrium from reserpine-treated guinea pigs. This negative inotropic response was unaffected by the addition of atropine to the perfusion fluid, and it was highly sensitive to changes in external Ca2+ concentration. Both in spontaneously beating and in electrically driven atrium, muzolimine (50-400 microM) antagonized, in an apparently competitive manner, the increase in contractile force induced by cumulative addition of CaCl2 (0.68-9.59 mM) to the bathing fluid. Muzolimine (50-100 microM) reduced the inotropic response to low (5-30 nM), but not high (50-100 nM) concentrations of Bay K 8644, a calcium-channel agonist. The inotropic effects of 8-phenyltheophylline and of ouabain were antagonized by muzolimine (10-100 microM) in a noncompetitive manner, while the response to noradrenaline was not altered. Similar to muzolimine, verapamil at a concentration suitable to block calcium channels inhibited, in a noncompetitive way, the inotropic effect induced by 8-phenyltheophylline and by ouabain without altering the contractile response to noradrenaline. Furosemide (10 and 100 microM) did not influence the contractile force or the frequency of spontaneously beating atria, nor the inotropic effect induced by CaCl2, 8-phenyltheophylline, ouabain, or noradrenaline. These results indicate that the influence of muzolimine on guinea-pig atria originates from an inhibition of Ca2+ influx into cardiac cells and that furosemide does not mimic the effect of muzolimine at this level.

Mechanism of the vasodilating action of etozoline and its metabolites in guinea-pig aorta.

The mechanism of the vasodilating action of the diuretic etozoline and of its metabolites d- and l-ozolinone was studied in isolated aortic strips from reserpine-treated guinea-pigs. Etozoline (10 microM to 1 mM) induced a concentration-dependent inhibition of the contraction evoked by increasing K+ concentrations (15 to 45 mM) in the perfusion medium. The inhibition was of a noncompetitive type. Etozoline also inhibited contractions induced by increasing Ca++ concentrations in the perfusion medium of aortic strips depolarized by 40 mM K+. The inhibition was concentration-dependent and of a noncompetitive type. Tetraethylammonium, at concentrations reported to increase Ca++ influx into smooth muscle cells by closing K+ channels, induced contractions of aortic strips that were highly sensitive to inhibition by etozoline. Analysis of the concentration-response curves for tetraethylammonium showed that the antagonism by etozoline was of a competitive type. The pA2 value for etozoline was 5.01 +/- 0.16. Also arterial spasm, obtained by prolonging the exposure of vascular strips to tetraethylammonium (30 min), was completely suppressed by etozoline. l- and d-Ozolinone antagonized tetraethylammonium-induced contractions of aortic strips in an apparently competitive manner, but only at very high concentrations (1 and 3 mM, respectively). These results suggest that the vasodilating action of etozoline and of its metabolites is mediated by an inhibition of Ca++ influx into smooth muscle cells following a specific opening of K+ channels, but only etozoline may act through this mechanism at concentrations likely to be operative in vivo.