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 ventricula function and, after cessation of training, variable degrees of regression. The racing greyhound is as animal with cardiac hypertrophy said to be part congenital and part exercise-induced. Racing grcy hounds underwent serial cardiac catheterization three times during an 8-month period after cessation racing/training to determine the functional consequences of the cessation of training. At the end ci 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 ol 12 greyhounds in the serially studied group showed increases in max dP/dt and dP/dt normalized to pressure of 50 mm Hg. Modified pre-ejection period and peak negative dP/dt also increased significantly (p<.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 or 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 carly (<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.