The cardiovascular effects of deconditioning after endurance training in rats.

The haemodynamic effects of endurance training and physical deconditioning were studied in anaesthetized rats using aortic and left ventricular pressure recordings and volume measurements by thermodilution method during isoproterenol and CaCl2 loads. The resting stroke volume was significantly larger in the training group (TG I, n = 10) than in the control group (CG I, n = 13). During the CaCl2 infusion stroke index, end-diastolic and end-systolic volumes increased in the TG I, but decreased in the CG I. Both isoproterenol and CaCl2 decreased systemic vascular resistance in the TG I, but increased it in the CG I. After a six-week deconditioning following training period (TG II, n = 10) stroke index, end-diastolic and end-systolic volumes decreased during CaCl2 and isoproterenol infusions similarly to the control deconditioning group (CG II, n = 12). These responses differed significantly from those observed in the TG I. Peripheral resistance increased in both the CG II and the TG II. Cardiac hypertrophy observed during training was partly reversed after the deconditioning period. In conclusion, endurance training improves the pumping performance of the rat heart by enhancing the diastolic filling of the left ventricle and decreasing peripheral resistance during inotropic load. Left ventricular contractility is not affected. A six-week deconditioning period after endurance training returns the haemodynamic changes to sedentary levels.