tropisetron and Coronary-Disease

1. The effects of 5-hydroxytryptamine (5-HT) were investigated on right atrial appendages obtained from patients treated with beta-adrenoceptor blocking agents who were undergoing open heart surgery. Atrial strips were paced under isometric conditions. 2. 5-HT increased contractile force to approximately one half of the force produced by a saturating concentration of (-)-isoprenaline. Both 5-HT and (-)-isoprenaline accelerated the onset of relaxation, as indicated by an abbreviation of time to peak force. 3. The effects of 5-HT were resistant to blockade by 0.4 microM (+/-)-propranolol, 1 microM (-)-pindolol, 0.4 microM methiothepin, 4 microM yohimbine, 0.4 microM ketanserin, 10 microM phenoxybenzamine, 1 microM methysergide, 2 microM MDL 72222 and 20 microM granisetron. 4. Cocaine 6 microM potentiated the effects of 5-HT, increasing the pEC50 from 6.6 to 7.4. The inotropic potency of 5-HT is five times greater than that of (-)-noradrenaline. 5. ICS 205930 antagonized competitively the effects of 5-HT with a pKB of 6.7. 6. In the presence of 0.4 microM (+/-)-propranolol, 10 microM 5-HT increased both adenosine 3':5' cyclic-monophosphate (cyclic AMP) levels and cyclic AMP-dependent protein kinase activity by approximately one half and two thirds respectively, of the corresponding effects of 200 microM (-)-isoprenaline. 7. Both the increase in cyclic AMP levels and the stimulation of protein kinase activity are consistent with the inotropic effects of 5-HT being mediated by cyclic AMP-dependent phosphorylation of Ca2+ channels and of proteins involved in contraction and relaxation. 8. The human atrial 5-HT receptor resembles the neuronal 'so called' 5-HT4 receptor of rodents both in increasing cyclic AMP levels and in its affinity for ICS 205930.

Topics: Cocaine; Coronary Disease; Cyclic AMP; Female; Humans; In Vitro Techniques; Indoles; Isoproterenol; Male; Middle Aged; Myocardial Contraction; Myocardium; Protein Kinases; Receptors, Serotonin; Serotonin Antagonists; Tropisetron

The effects of ICS 205-930 [3 alpha-tropanyl)-1H-indole-3-carboxylic acid ester), an antagonist of 5-HT at neuronal M receptors, were examined in anaesthetised greyhounds subject to acute coronary artery occlusion and reperfusion. Intravenous administration of 0.3 or 2.0 mg kg-1 of ICS 205-930 did not significantly alter haemodynamics or blood gases. The higher dose had marked antiarrhythmic activity. The total number of ischaemia-induced extrasystoles was reduced to 167 +/- 64 compared with 467 +/- 99 in controls. Ventricular fibrillation induced by reperfusion after 40 min of ischaemia was also significantly reduced from 80 to 33%. Immediately following release of the coronary artery occlusion significant increases in plasma noradrenaline and dopamine concentrations were detected in local coronary venous blood draining from the ischaemic area in control dogs. This catecholamine release was also evident in the dogs which received 2 mg kg-1 ICS 205-930 but was less marked. Thus the antiarrhythmic activity of ICS 205-930 may be related to antagonism of detrimental effects of 5-HT, such as the ability to facilitate the release of noradrenaline from sympathetic nerve terminals in the heart, although other mechanisms may be involved.

Topics: Animals; Anti-Arrhythmia Agents; Arrhythmias, Cardiac; Catecholamines; Coronary Disease; Dogs; Dopamine; Epinephrine; Female; Hemodynamics; Indoles; Male; Norepinephrine; Tropisetron