Effects of the cessation of training on left ventricular function in the racing greyhound. Serial studies in a model of cardiac hypertrophy.

Exercise-induced cardiac hypertrophy has been associated with normal resting left ventricular function and, after cessation of training, variable degrees of regression. The racing greyhound is an animal with cardiac hypertrophy said to be part congenital and part exercise-induced. Racing greyhounds underwent serial cardiac catheterization three times during an 8-month period after cessation of racing/training to determine the functional consequences of the cessation of training. At the end of 8 months of inactivity the animals' hearts were excised and weighed in order to compare heart weight/body weight (HW/BW) ratios with those obtained in a group of racing greyhounds killed within one month, 19 +/- 16 days (mean +/- SD), of the cessation of training. Comparison of HW/BW ratios failed to reveal a significant difference between the serially studied group, 12.1 +/- 1.9 g/kg (mean +/- SD), and the more recently exercising group, 12.7 +/- 1.4 g/kg (mean +/- SD) of dogs. After 2 months of inactivity, 9 of 12 greyhounds in the serially studied group showed increases in max dP/dt and dP/dt normalized to a pressure of 50 mmHg. Modified pre-ejection period and peak negative dP/dt also increased significantly (p less than .004) during this same period. No further changes in these variables were found at the final 8-month study. Our failure to demonstrate a difference in HW/BW ratios between these two groups of dogs suggests that the exercise-induced component of cardiac hypertrophy in the trained racing greyhound is probably very small and, if it exists, regresses very early (less than 1 month). Changes in contractility indices that were observed occurred after this time period (between 1 and 2 months) and are therefore probably not due to regression of cardiac hypertrophy.