Abstract
Depression of transmission through the superior cervical ganglion after intra-arterial injection of epinephrine differs from the depression which follows administration of classic ganglionic blocking drugs. Epinephrine (E) caused a greater depression of transmission at low stimulus frequencies than at high stimulus frequencies. The S-1 and S-2 spikes and P potential of the ganglion action potential were relatively sensitive to the effect of E, but the S-4 spike was resistant. Complete block of transmission was not obtained with doses of E up to 1000 μg. No difference in block was observed with maximal or submaximal stimulus strengths. The E effect was antagonized by phenoxybenzamine. Norepinephrine (NE) and dopamine were less potent than E in reducing ganglionic transmission. Tyramine had a biphasic effect. A depression of transmission, qualitatively different from E and resistant to antagonism by phenoxybenzamine, occurred immediately after injection. After a short recovery phase, another depression (2–5 min after injection) occurred. The late depression was qualitatively similar to the E effect. E usually caused a small depolarization of the ganglion, but this depolarization was unrelated to the time course or magnitude of the depression of the S-2 spike.
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