Postnatal development of rat heart during 6-hydroxydopamine or propranolol treatment

Progressive postbirth development of mammalian heart contractile function is accompanied by augmentations of aerobic metabolic potential and cardiac myofibrillar ATPase activity. The temporal similarity of the above developmental sequences suggested that a single, unifying factor may coordinate myocardial maturation. It was hypothesized that cardiac sympathetic nervous system development might be regulating other aspects of myocardial growth. To test this hypothesis, previously well-defined aspects of heart metabolism and contractile protein ATPase activity were determined in rats which were either sympathectomized with 6-hydroxydopamine (6-OHDA) or subjected to chronic, beta-adrenergic blockade (propranolol) throughout the postbirth period from 3 to 6 weeks of age. Neither 6-OHDA treatment nor chronic, beta-adrenergic blockade resulted in a significant reduction of any metabolic enzyme specific activity or in myofibrillar ATPase. Myofibrillar creatine phosphokinase (CPK) activity underwent greater enhancement relative to ATPase during normal heart growth. Significant and divergent influences were exerted by 6-OHDA and propranolol drug regimens on myofibrillar CPK/ATPase enzyme activity ratio. These results indicate (a) the potential for independent regulation of myofibrillar CPK and ATPase, and (b) the advisability of evaluating CPK, ATPase, and CPK/ATPase enzymatic activities as myofibrillar correlates of heart contractile function. Nevertheless, the majority of developmentally related processes in the heart are minimally influenced by chemical sympathectomy.