Studies of systolic mechanics and diastolic behavior of the left ventricle in the trained racing greyhound

Despite much interest in the effects of exercise on the myocardium, and the need to develop animal models which mimic conditions leading to cardiac hypertrophy, little attention has been focused on the trained racing greyhound. The current study compared two groups of anesthetized trained racing greyhounds (a total of 20 animals, 12 of whom were maintained for serial studies and 8 of whom were sacrificed for anatomic correlations) with 3 detrained greyhounds and 6 comparably sized mongrels. Systemic blood pressures, right and left heart pressures, ventricular mechanics and indices of diastolic behavior were compared. All measured indices of contractility (dp/dt, dp/dtDP₄₀, V_ce and V_max) were lower in trained racing greyhounds than in mongrels although none achieved statistical significance. No significant difference in diastolic behavior was found between trained greyhounds and mongrels. While caution should be applied because of the small numbers of animals and the use of anesthesia, the lower than expected contractility found in trained racing greyhounds may reflect increased parasympathetic tone in the immediate post-training period. The normal diastolic behavior of the trained greyhound left ventricle contrasts to abnormal diastolic behavior found in models of chronic pressure overload.