Effects of catecholamines on sympathetic evoked action potentials in the stellate ganglion of the cat.

It is well known that catecholamines significantly modify the sympathetic ganglionic transmission (1-10). Since Eccles and Libet (7) proposed a model of ganglionic transmis sion characterized by adrenergically mediated hyperpolarizing potentials, many reports have appeared concerning the action and the physiologic role of catecholamines in sympa thetic ganglia. De Groat and Volle (9) have investigated the effect of catecholamines on the transmission in the superior cervical ganglion of the cat, and they postulated two phar macologically distinctive adrenoceptive sites in sympathetic ganglia, αand β-receptors responding to the drugs with depression and facilitation, respectively. According to this concept, the enhancement of ganglionic transmission by small doses of epinephrine and norepinephrine (3, 6) might be attributed to the activation of adrenergic ganglionic β-receptor, however, findings are not consistent with those of others who failed to demonstrate such an enhancement (1, 4, 5). Thus, reports on the catecholamine effects on sympathetic ganglia are still in dispute. The action of catecholamines on sympathetic ganglia has been studied mostly on the superior cervical ganglion, with only a few studies on the stellate ganglion (4, 5). In our preliminary studies on the efferent discharge of cardiac sympathetic nerve, a depressant action of epinephrine was demonstrated on the stellate ganglion. The finding led us to a further investigation of the effect of catecholamines on this ganglion. In the present experiment, changes in the amplitude of sympathetic evoked action potentials were observed in postganglionic fibers of the stellate ganglion. It is evident that most sympathetic nerves towards the heart synapse with the stellate ganglion. In order to examine the physiologic role of catecholamines in sympathetic activities in cardiovascular system, changes in intra ventricular pressure caused by the preganglionic nerve stimulation were monitored during topical application of catecholamine to the ganglion.