ABSTRACT
The ability of the B-receptor blocker, timolol and the Ca[2+] channel antagonist prenylamine to limit infarct size [I.S.] was assessed in cats, 5 hours after ligation of the left anterior descending coronary artery [LAD]. In control untreated cats, the S-T segment was raised significantly 30 min. after ligation to reach a value of 0.7 +/- 0.09 MV and was maintained significantly elevated [0.67 +/- 0.07 MV] to the end of the experiment. Ventricular dysrhythmia occurred in 3 out of 6 cats and ended in one of them by ventricular fibrillation and death. Serum CPK level increased significantly from a pre-occlusion level of 94 +/- 5 U/L to reach 724 +/- 60, 5 hours later. The I.S., measured by planimetry in serial cardiac sections, stained by triphenyl tetrazolium stain, was found to measure 315 +/- 34 mm[2] representing 31.67% of the heart. Timolol, given in a dose of 25 ug/kg i.v., 15 min. before ligation of LAD, induced hypotension, sinus bradycardia and decreased S-T segment elevation significantly to 0.13 +/- 0.04 MV. It prevented ventricular dysrhythmia and fibrillation. Timolol also reduced significantly serum CPK level to 195 +/- 17 U/L and I.S. to 9.18%. I.V. administration of prenylamine in a dose of 3 mg/kg was accompanied by sinus bradycardia, and hypotension. The S-T segment was significantly lowered [0.15 +/- 0.04 MV] and ventricular fibrillation was prevented. Both serum CPK level [193 =/- 25 U/L] and I.S. [12.93] were significantly reduced when compared with the corresponding levels in coronary ligated untreated cats. It is concluded that, both timolol and prenylamine could protect the heart against extension of infarct size and its complication. An effect which might be due to decrease in free cytosolic Ca[2+] or through their haemodynamic effects which reduce the cardiac work