Abstract

Catecholamine content, in both normal and extrinsically denervated dog hearts, was determined in discrete areas of contractile myocardium. These sites were compared with samples from the cardiac conduction system and immediately subjacent tissue. Either surgical or chemical, 6-hydroxydopamine denervation produced striking reductions in both epinephrine (E) and norepinephrine content of contractile tissues and essentially complete loss of norepinephrine from conductile tissue. Neither procedure was similarly effective in reducing E levels in conductile tissue. The contractile tissue norepinephrine appears to be completely associated with nerve terminals, with only 1 to 5% of the catecholamine remaining in sites which survive neural degeneration. The corresponding E levels remaining after denervation (40-50% of control in contractile and 73% in conductile tissue) support the concept of a separate store for the majority of this catechohamine. In addition, bretylium tosylate appears to have a paradoxical enhancing effect on the E levels in the conduction system in both normal and denervated animals. These data appear to support the concept that a significant portion of time cardiac E storage associated with the conduction system is held in non-neuronal stores either in chromaffin cells, in the specialized cells themselves or in cardiac analogs of chromaffin cells.