Exercise and cardiac performance capacity in rats with partial sympathectomy.

This study was undertaken to examine maximal oxygen uptake (VO2 max) and heart rate (HR) during exercise, in situ derived cardiac contractile capacity, and Ca2+ regulation of cardiac myofibril ATPase in normal female rats and in rats with partial sympathectomy (SYMX) induced by chronic injections of guanethidine. Also, normal control (NC) rats were studied during exercise with and without the beta 1-blocking drug atenolol. The results show that SYMX did not have any effect on Ca2+-regulated cardiac myofibril ATPase activity. Also similar cardiac functional capacity, as reflected in left ventricular pressure development and +dP/dtmax, was observed for both groups when the heart was stressed by either exogenous norepinephrine or maximal afterload (aortic constriction). Exercise VO2 max was reduced by 15% (P less than 0.05) in the SYMX compared to the NC group. Although this reduction in VO2 max corresponded to a parallel reduction in HRmax, NC rats with cardiac beta-blockade attained normal VO2 max even though their exercise HRmax was below the SYMX group. These findings suggest that normal rats with attenuated HR and contractility have a better capacity to acutely maintain VO2 max during exercise than rats with chemical sympathectomy.