The effects of aging on the electrophysiologic responses to verapamil in isolated perfused rat hearts.

The effects of aging on heart rate and atrioventricular (AV) conduction responses to verapamil (0-100 ng/ml) were studied in Langendorff perfused hearts from 12 mature (4-6 months) and 12 senescent (24 months) male Fischer 344 rats and in hearts from 10 mature and 9 senescent rats after reserpine administration (0.25 mg/kg/day i.p. for 5-7 days). During 30 min of perfusion with verapamil concentrations of 0, 10, 20, 50 and 100 ng/ml in the absence of reserpine administration, intervals between atrial electrograms (A-A intervals), paced AV conduction time and AV Wenckebach cycle lengths increased in hearts from all animals (P less than .001). A-A intervals increased more in senescent vs. mature animals (with marked slowing in 3/12 senescent and 0/12 mature at 100 ng/ml), spontaneous AV Wenckebach block occurred more frequently in hearts from senescent animals (in 7/12 senescent and 1/12 mature, P less than .07) and AV Wenckebach cycle length increased more in senescent vs. mature hearts (from 123 +/- 11 to 294 +/- 108 msec, mean +/- S.D., in mature vs. 154 +/- 16 to 458 +/- 10 msec in senescent hearts). Reserpine administration did not significantly alter qualitative responses to verapamil, but accentuated age differences in responses at higher verapamil concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)