Regional distribution of tyrosine hydroxylase and dopamine β-hydroxylase activities in guinea pig heart

The sympathetic and parasympathetic autonomic nervous systems regulate heart rate and myocardial contractility. Using sensitive radioisotopic assays, we examined the regional distribution of tyrosine hydroxylase and dopamine β-hydroxylase activity, which are markers for sympathetic autonomic innervation, in specialized pacemaker and conduction tissue and in contractile heart tissue. Of the 20 regions of guinea pig heart examined, we find that the highest activities occur in the sinoatrial node and the right atrial appendage. Intermediate activity occurs in the left atrium, interatrial septum and right ventricular papillary muscle. Activities in the remainder of the heart are lower and rather uniform. Comparing the enzyme markers for the parasympathetic [17] and sympathetic system, we find that these systems have different distribution. The former, for example, is closely associated with the specialized pacemaker and conduction system including the sinoatrial and atrioventricular nodes and regions rich in Purkinje fibers. The sympathetic system, on the other hand, is associated with both contractile and conducting tissue.