In vitro characterization of a novel Ca2+ entry blocker: SR 33805.

In this study, SR 33805 was shown to inhibit competitively [3H]fantofarone binding to cardiac sarcolemmal membranes. In contrast, SR 33805 was shown to inhibit allosterically [3H](+)-PN200-110, [3H](-)-D888 and cis-(+)-[3H]diltiazem binding. In isolated rabbit atrial preparations, SR 33805 was shown to be the least potent of fantofarone, nifedipine, verapamil and diltiazem in terms of both negative chronotropic and inotropic responses (IC50's 6 and 12 microM, respectively). In superfused rat aortic strips, SR 33805 like other Ca2+ channel antagonists, caused a significant inhibition of both K(+)-induced 45Ca2+ influx and contractile responses. In addition this agent was shown to antagonize Ca(2+)-induced contractions in K(+)-depolarized aorta with a pA2, value of 8.39 +/- 0.02. In femoral, renal and basilar arteries, SR 33805 was equiactive to the other Ca2+ channel antagonists studied in antagonizing K(+)-induced contractions (IC50 approximately 40 nM), but unlike the reference Ca2+ channel antagonists, was equiactive in antagonizing serotonin-induced contractions (IC50 approximately 250 nM). This suggests that the effects of SR 33805 depend mainly on membrane potential. In conclusion, SR 33805 is a potent Ca2+ channel antagonist which, unlike fantofarone, verapamil and diltiazem, is highly selective for vascular smooth muscle and devoid of any potent negative inotropic actions.

Novel heterocyclic analogues of the new potent class of calcium entry blockers: 1-[[4-(aminoalkoxy)phenyl]sulfonyl]indolizines.

Several heterocyclic analogues of the potent 1-[[4-(aminoalkoxy)phenyl]sulfonyl]indolizines were synthesized and evaluated for their antagonistic calcium activities in comparison with the 1-sulfonylindolizine SR 33557 and the usual calcium antagonist references verapamil, cis-(+)-diltiazem, and nifedipine. The bicyclic nine-membered rings were, in general, more potent than the bicyclic 10-membered or five-membered rings. Among the bicyclic nine-membered rings, the indole nucleus appeared to be extremely favorable to support the calcium antagonistic activity. In particular, compound 36, with an IC50 value for the inhibition of [3H]nitrendipine equal to 0.072 nM, is among the most potent calcium antagonist known. This compound has been selected for clinical development.

A novel class of calcium-entry blockers: the 1[[4-(aminoalkoxy)phenyl]sulfonyl]indolizines.

The synthesis and initial biological evaluation of a series of 1-sulfonylindolizines is described. These compounds have been shown to be representatives of a novel class of potent, slow-channel calcium antagonists. All compounds were found to be at least as active as the reference calcium antagonists verapamil and cis-(+)-diltiazem. Structure-activity relationship studies have shown that all compounds possessing an aralkyl group in the amine moiety and an isopropyl or cyclopropyl group at the 2 position of the indolizine are among the most potent calcium antagonists known outside the 1,4-dihydropyridine series. The IC50 values for the inhibition of [3H]nitrendipine binding vary between 0.19 and 4.5 nM whereas the IC50 value for nifedipine is 2.5 nM. One of the compounds in this group (9ab) has now been selected for clinical development.

Prehospital thrombolysis in acute myocardial infarction.

The benefit and risk of prehospital thrombolysis for acute myocardial infarction (AMI) were evaluated in a double-blind randomized trial. Patients presenting less than 4 hours after symptom onset received 2 million units of urokinase as an intravenous bolus either before (group A, n = 40) or after (group B, n = 38) hospital admission. The mean time interval from onset of symptoms to thrombolytic therapy was 85 +/- 51 minutes in group A and 137 +/- 50 minutes in group B (p less than 0.0005). In 91% of the patients, thrombolytic therapy was administered less than 3 hours after symptom onset. Complication rates during the pre- and in-hospital period were low and did not differ between groups. Three patients died (1 in group A, 2 in group B) from reinfarction 7 to 14 days after admission. Left-sided cardiac catheterization before discharge revealed a patency rate in the infarct-related artery of 61% in group A and 67% in group B (difference not significant). Global left ventricular function and regional wall motion at the infarct site did not differ significantly between group A and B (ejection fraction 51 +/- 10%, n = 28 vs 53 +/- 14%, n = 28; wall motion -2.3 +/- 1.3 vs -2.2 +/- 1.1 standard deviation, respectively). Also, peak creatine kinase did not differ significantly (838 +/- 634 U/liter in group A vs 924 +/- 595 U/liter in group B). Prehospital thrombolysis using a bolus injection of urokinase has a low risk when performed by a trained physician with a mobile care unit. The saving of 45 minutes in the early stage of an acute infarction through prehospital thrombolysis did not appear to be important for salvage of myocardial function.

SR 33557, a novel calcium entry blocker. I. In vitro isolated tissue studies.

The effects of SR 33557 on isolated cardiovascular preparations were compared to those of nifedipine, verapamil and diltiazem. In rat aortic strips, SR 33557, like nifedipine, verapamil and diltiazem, caused a significant and simultaneous inhibition of potassium-induced 45Ca++ influx and contractile responses (nifedipine greater than SR 33557 greater than verapamil greater than diltiazem). SR 33557 also antagonized Ca(++)-induced contractions in K(+)-depolarized aorta preparations (pA2:9.08 +/- 0.03) and is the first calcium channel antagonist, structurally not related to 1,4-dihydropyridines, to inhibit competitively contractions induced by BAY K8644. In spike-generating vascular smooth muscle (rat portal vein), contractures evoked by noradrenaline (4 microM) or KCl (100 mM) were reduced by all four antagonists, the pharmacological potency being nifedipine greater than SR 33557 greater than verapamil greater than diltiazem. Unlike SR 33557, nifedipine, verapamil and diltiazem showed a parallel enhancement of frequency of spontaneous contractions in rat portal vein in spite of a concentration-related reduction in amplitude. By using rabbit atrial preparations, spontaneous right atrial rate and electrically stimulated (120/min) basal contractions of left atria were used as indices of chronotropy and inotropy. The potency series for negative chronotropic effects was nifedipine greater than SR 33557 greater than verapamil greater than diltiazem. For negative inotropic effects the potency order was verapamil greater than nifedipine greater than SR 33557 greater than diltiazem, respectively. Thus, SR 33557 should depress heart rate to a greater extent than ventricular contractility. These results suggest that SR 33557 is a potent calcium entry blocker that (unlike verapamil and diltiazem) is particularly selective for vascular smooth muscle and devoid of any potent negative inotropic actions.

SR 33557, a novel calcium-antagonist: interaction with [3H]-(+/-)-nitrendipine and [3H]-(-)-desmethoxy-verapamil binding sites in cerebral membranes.

We investigated the pharmacological properties of SR 33557, a novel compound with calcium-antagonist properties, in both functional tests in vitro and radioligand binding studies. SR 33557 potently antagonized calcium-induced contraction of potassium-depolarized rat aorta in vitro with an IC50 value of 5.6 +/- 0.9 nM, but was a much weaker inhibitor of noradrenaline-induced contraction of the same tissue (IC50 = 96 +/- 22 nM). SR 33557 totally inhibited [3H]-(+/-)-nitrendipine binding to rat brain membranes with a Ki value of 0.19 +/- 0.03 nM. Diltiazem, which used alone increases [3H]-(+/-)-nitrendipine binding, reversed this inhibition indicating that SR 33557 allosterically regulates [3H]-(+/-)-nitrendipine binding. SR 33557 also fully inhibited [3H]-(-)-desmethoxyverapamil binding to cerebral membranes, but inhibition curves were biphasic. IC50 value calculated for that part of the curve which reflects the high affinity binding site of SR 33557 (IC50 = 0.20 +/- 0.02 nM) was very similar to the Ki value determined for inhibition of [3H]-(+/-)-nitrendipine binding. Kinetic evidences indicate that SR 33557 binds to a site which is distinct from the 1,4-dihydropyridine or the phenylalkylamine binding sites associated with the calcium channel. To test the pharmacological specificity of these interactions, the ability of SR 33557 to interact with eight other receptors in cerebral or heart membranes was assessed by binding assays. No high-affinity interaction was observed between SR 33557 and any of the receptors investigated. We conclude that SR 33557 binds specifically and with a high affinity to a site closely associated with the voltage-operated calcium channel in cerebral membranes.

Antipyretic analgesics inhibit prostaglandin release from astrocytes and macrophages similarly.

The effect of acid and non-acid antipyretic analgesics on prostaglandin (PG) release from cultured mouse astrocytes and peritoneal macrophages was investigated in order to test the hypothesis that the non-acid compounds are more potent inhibitors of PG formation in brain than in peripheral tissues. Stimulation of the cells by the divalent cation ionophore A 23187 (10(-6) mol/l) induced PG release from astrocytes and macrophages (mainly PGD2 and PGE2, respectively). This PG release was inhibited by acetylsalicylic acid (10(-5) - 10(-6) mol/l) and indomethacin (10(-6) - 10(-9) mol/l) but also by high concentrations (10(-3) - 10(-5) mol/l) of the non-acid compounds 4-methyl-aminophenazone, the main active metabolite of dipyrone (metamizol), and acetaminophen (paracetamol). No difference was found in the inhibitory potency of the drugs in astrocytes and macrophages, suggesting that a specific sensitivity of brain cells toward non-acid antipyretic analgesics does not contribute to their analgesic effect.

Nature of the antiadrenergic properties of an indolizine.

Inhibition by 2-ethyl-3-(4-y-di-n-butylaminopropoxybenzoyl)-indolizine hydrochloride (L 9394) and by propranolol of the positive chronotropic effect of isoproterenol on spontaneously beating rabbit right atria has been studied in vitro. Propranolol behaved like a typical competitive beta 1-adrenoceptor antagonist with a pA2 value of 8.33. L 9394 acted as a non-competitive inhibitor with a pD'2 value of about 4.98. Inhibition by L 9394 and phentolamine of the norepinephrine-induced contractions of isolated rat aortic strips has been studied likewise. Phentolamine inhibited the adrenergic alpha-adrenoceptor competitively with a pA2 value of 8.69 while L 9394 behaved like a dual inhibitor, with a competitive component (pA2 value of 6.35) and a non-competitive component (pD'2 value of about 4.72).

The effects on cardiac muscle and nerve of a fluorinated decahydroquinoline derivative, L7810, rapidly absorbed after oral administration.

1. L7810 (4-carbamoyloxy-1-(4-(4-fluorophenyl)-4-oxobutyl) decahydroquinoline, has a local anaesthetic action on frog nerve 1.75 times that of procaine.2. L7810 protected anaesthetized guinea-pigs against ouabain-induced ventricular fibrillation and increased the lethal dose of ouabain.3. L7810 reduced the rate of rise of intracellularly recorded action potentials in rabbit isolated atria; the resting potential was not affected, but the duration of the action potential was prolonged.4. Unlike most drugs with local anaesthetic properties L7810 did not depress contractions in isolated atria but increased them.5. L7810 reduced the spontaneous frequency, maximum follow frequency and conduction velocity of rabbit isolated atria.6. L7810 had no blocking action on the chronotropic or positive inotropic actions of isoprenaline on isolated atrial muscle.7. In anaesthetized dogs L7810 caused a small dose-related bradycardia, and a large dose-related decrease in peripheral vascular resistance. There was no blockade of the effects of isoprenaline on heart rate or peripheral blood flow.

The effect of prolonged treatment with oxyfedrine on intracellular potentials and on other features of cardiac function in rabbits and guinea-pigs.

1. Previous work in acute experiments has shown that the main pharmacological action of oxyfedrine is stimulation of beta-adrenoceptors, yet there have been clinical reports that the drug is beneficial in the treatment of angina pectoris.2. In the present experiments rabbits and guinea-pigs were treated for several weeks with daily i.p. injections of oxyfedrine.3. A daily dosage of 15 mg/kg oxyfedrine had no effect on growth rate for 4 weeks, but thereafter the growth rate of treated animals fell below that of controls.4. The heart weights of the treated animals, expressed as a percentage of body weight, were significantly lower than those of controls.5. Measurement of intracellular potentials in hearts taken from treated rabbits showed that the main effects were a reduction in the maximum rate of depolarization and a prolongation of the plateau of the action potential.6. Guinea-pigs treated for 6 weeks with 15 mg/kg oxyfedrine daily i.p. were protected to some extent from the toxic effect of ouabain infused intravenously.