Substance P Effects on the Long-Term Regulation of Adrenal Catecholamine Levels

The classical view of secretion from the adrenal medulla was that of a relatively simple system. Since the early 1930s it has been known that release of acetylchol ine (ACh) from the stimulated splanchnic nerve causes secretion of the catecholamines, adrenaline and noradrenaline, from adrenal chromaffin cells [1]. In addition to these acute effects on catecholamine release, long-term stimulation of chromaffin cells with ACh (in a time course of hours to nays) was later found to produce other biochemical changes in the cell. A well-studied example of this is the ability for long-term stimulation with ACh to induce synthesis of tyrosine hydroxylase (TOH, EC 1.14.16.2), the rate-limiting enzyme in catecholamine synthesis [2]. Thus ACh can produce two types of responses in chromaffin cells. These responses differ in their time courses (one acute and one long-term) and also in their ionic dependences (ACh-stimulated catecholamine release is strictly Ca 2t-dependent [3], while ACh-stimulated induction of TOH is not [4]).