Association between the increase of cAMP content and the trans-synaptic induction of tyrosine hydroxylase in rat adrenal medulla

Abstract

When dexamethasone 0.25 or 2.5 μmole/kg i.p. was injected 2 h before reserpine (16 μmol/kg i.p.) the time course of the increase in cAMP content of rat adrenal medulla was changed. Reserpine alone caused a monophasic increase lasting between 1–2 h; reserpine after dexamethasone caused a biphasic increase: the immediate response, lasting between 15 and 30 min, was followed by a secondary increase beginning 2–3 h after reserpine and lasting for several hours. The overall increase in cAMP content elicited by reserpine during the 8 h following injection remained unchanged or was even increased, depending on the dose of dexamethasone. Pretreatment with dexamethasone, which delayed the increase in cAMP, also delayed the activation and translocation of protein kinase and the induction of tyrosine hydroxylase caused by reserpine in adrenal medulla. The action of reserpine on the cAMP content of adrenal medulla required an intact innervation and did not appear to be related to increased secretion of ACTH from pituitary. In denervated adrenals reserpine failed to increase the cAMP content of the medulla but not that of the cortex.