Dissociation between changes in cyclic AMP and subsequent induction of TH in the rat superior cervical ganglion and adrenal medulla

Summary Changes in the levels of cyclic AMP were studied in the superior cervical ganglion and adrenal medulla of male Sprague-Dawley rats under experimental conditions which lead to a trans-synaptic induction of tyrosine hydroxylase (TH) in these organs.In the superior cervical ganglion an intermittent 2-hour swimming stress or treatment with reserpine (5 or 10 mg/kg s.c.) failed to change cyclic AMP levels significantly (P>0.1) while 48 h later TH was markedly (P<0.001) increased. In the adrenal medulla the increase in cyclic AMP occurring during cold exposure was much greater than that observed during swimming stress. However, the increase in TH activity resulting from swimming stress was markedly greater then that resulting from cold exposure. The same inverse relationship holds true when comparing the effect of reserpine with that of cold stress. Moreover, during cold exposure cyclic AMP levels were maximal (700%) within 20 min and had fallen almost to control levels (180%) after 60 min. However, no significant increase in TH (P>0.1) was observed 48 h after a 1-hour cold stress whereas a 2-hour cold stress produced a marked (P<0.001) increase in TH activity. Thus, the second hour of cold stress during which cyclic AMP was only marginally elevated seems to be essential for initiating the biochemical events ultimately leading to an increased synthesis of TH.It is concluded that either cyclic AMP is not involved in trans-synaptic induction of TH or that changes in a small pool are essential and are overshadowed by a much larger pool of cyclic AMP not reacting in the same way.