Nerve stimulation in vivo acutely increases tyrosine hydroxylase activity in the superior cervical ganglion and its end organs.

Previous studies have shown that preganglionic nerve stimulation in vitro increases acutely the activity of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis, in sympathetic neuronal cell bodies in the rat superior cervical ganglion (SCG). In the present study, we have examined whether a similar increase occurs after nerve stimulation in vivo, and whether this enzyme activity also increases in sympathetic nerve terminals in autonomic end organs. Immediately following stimulation at 10 Hz for 15 min in vivo, TH activity was found to have increased 4- to 8-fold in the SCG and in 3 of its end organs: the iris, the pineal gland and the submaxillary gland. These results indicate that increases in sympathetic nerve activity in vivo can lead to increases in TH activity both in adrenergic cell bodies/dendrites in the SCG and in adrenergic nerve terminals/fibers in various autonomic end organs.