Effect of adrenalectomy on tyrosine hydroxylase activity.

Bilateral adrenalectomy produced a fall in blood pressure and an increase in tyrosine hydroxylase activity in the superior cervical ganglion in the rat. The fall in blood pressure and the increase in tyrosine hydroxylase activity in the superior cervical ganglion were prevented by giving the adrenalectomized animals 0.9% saline as their only drinking fluid. The increase in tyrosine hydroxylase activity was also prevented by decentralization (severing the preganglionic fiber) of the superior cervical ganglion. These results suggest that the induction of tyrosine hydroxylase activity results from a reflexly mediated increase in nerve impulse traffic that results from the adrenalectomy-induced fall in blood pressure. Further characterization of this response showed that the glucocorticoid, dexamethasone, did not cause a further induction of enzyme in adrenalectomized rats whereas, treatment with epinephrine as well as dexamethasone, did result in an augmentation of the enzyme activity above that seen in the already induced adrenalectomized animals.