The effects of
cardiac hypertrophy on the structure, function and tolerance to
ischemia of rat hearts have been investigated. Multiple
injections of low doses of
isoproterenol (ISO) resulted in an increase of heart
weight/body weight ratio by 60%, and a decrease of
myocardial creatine kinase activity by 25%, as compared to normal rats. Compared to age-matched control rats, rats submitted to a swimming program had a higher heart weight by 20%, but similar values of heart weight to
body weight ratio. In isolated perfusion, the functional capacities of hearts from ISO-treated rats were severely depressed compared to normal rat hearts whereas exercise-trained rat hearts performed as well or even better than control hearts. The functional recovery of ISO-treated hearts following
cardioplegia-induced arrest for 20 min at 37 degrees C was significantly worse than the recovery of normal hearts, but hearts of exercise-trained rats showed a significantly better recovery than control hearts. Exercise training results in improvement of myocardial blood supply resulting in better preservation of the heart during
ischemia, compared to normal hearts. Addition of a combination of
verapamil and
diltiazem to the
cardioplegic solution followed by ischemic arrest for 20 min at 37 degrees C resulted for ISO-treated rat hearts in an improved recovery of cardiac output (99%) compared to
cardioplegia in the absence of these drugs (72%). In exercise-trained and control rat hearts,
calcium antagonists improved the recovery from cardioplegic arrest of cardiac output from 90% to 92% and from 71% to 87%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)