Effects of the calcium antagonistic compound nifedipine alone and combined with nitrites on the mechanical performance and the relaxation of hypoxic and reoxygenated myocardium

Abstract

The purpose of the present study was to investigate the effects of low concentrations of nifedipine on the cat myocardium under normal conditions, and during hypoxia with subsequent reoxygenation, and, thus, to find out whether the protective effect on hypoxic myocardium described by different investigators existed at these levels. Experiments carried out on five series of each 10 papillary muscles showed that: (1) Nifedipine (0.02 μg/ml) exerted a negative ino tropic effect on maximum unloaded velocity of shortening and total force (V _max : 92.91 ± 2.92%; PF: 92.10 ± 2.60%), whereas depression of peak velocity of relaxation became marked only at 0.2 μg/ml (V _relax : 88.87 ± 3.91%). This dose-dependent effect is also Ca ^{$ $} -dependent. (2) Nifedipine (0.02 μ/ml) protected against the depression of V _max , PF and V ^relax during hypoxia (PO ₂ = 25 mm Hg) V _max : 82.60 ± 3.45% v. 78.45 ± 1.35% control; PF: 54.65 ± 4.41% v. 48.74 ±3.51% and V _relax : 92.55 ± 4.50% v. 68.47 ± 1.30%). (3) The association of nifedipine (0.02 μ/ml) and nitroglycerin (0.3 μ/ml) accelerated the recovery of the depression of peak velocity of relaxation during reoxygenation (V _relax : 99.90 ± 5.63% v. 89.96 ± 5.15% nifedipine alone).