| Abstract: | Phenylethanolamine-N-methyltransferase activity of rat hypothalami was assayed. The enzyme was present at birth, in traces, and gradually increased during the first 2 postnatal months. Exposure to recurrent stressful situations increased PNMT activity in a statistically significant manner. Persistence of exposure to stressful events resulted in higher adult PNMT activity. Assays of hypothalamic tissue cultures revealed that part of PNMT activity increase was due to temporary potentiation by local factors, and partly to increase of tissue concentration of enzyme by increased protein synthesis. One of the submolecular chain reactions generated by stress (and able to induce protein synthesis) was identified as: release of ACTH during stress, activation of local adenylate cyclase by ACTH to synthesize cyclic AMP. When released, this cyclic AMP increased the local cyclic AMP: cyclic GMP ratio, a process known to induce protein synthesis. A potent and selective competitive inhibitor, SK&F 64139, when added to tissue cultures, prevented increase of PNMT activity by prolonged stimulation. |
