[Effects of nitroglycerin and nifedipine on stunned myocardium due to brief repeated ischemias].

OBJECTIVE

To analyze whether nitroglycerin and nifedipine can reduce myocardial stunning due to very brief, repeated coronary ischemias.

MATERIAL AND METHODS

In 33 anaesthetized and open chest dogs, the lengthening and shortening fractions were analyzed with ultrasonic crystals in the ischemic and control myocardial areas. Twenty repeated coronary occlusions of 2 minutes each, with a recovery time of 3 minutes between each occlusion, were induced. At the beginning of the experiment, nitroglycerin (0.3 mg i.v. and 80 micrograms/kg/min perfusion) was administered in series A (n = 8), nifedipine (5 mu/kg i.v. and 1 microgram/kg/min perfusion) in series B (n = 9). The results were compared with control results (n = 16) without drugs.

RESULTS

Changes in the shortening fraction of the ischemic area during coronary occlusions were similar in all three series; after the last occlusion the shortening fraction in the control series was -14.9% with respect to basal values, -14.6% in series A and -16.6% in series B. Sixty minutes after the last ischemia, the shortening fraction impairment in respect to the basal values was larger in the control series (-18.9%) and in series A (-16.9%). In series B there was recovery (-13.5%) (p < 0.05 vs control series).

CONCLUSIONS

Our study indicates that nitroglycerin does not seem to have cardioprotective effects against brief, repeated ischemia. However, nifedipine decreases postischemic dysfunction due to this model of ischemia, probably by avoiding the intracellular Ca overload produced during cardiac ischemia.