The release of 3H-1-methyl-4-phenylpyridinium from bovine adrenal chromaffin cells is modulated by somatostatin

Besides cholinergic regulation, catecholamine secretion from adrenal chromaffin cells can be elicited and/or modulated by noncholinergic neurotransmitters and hormones. This study was undertaken to investigate the influence of somatostatin and octreotide on 3H]MPP+ secretion evoked by KCl or cholinergic agents, from bovine adrenal chromaffin cells. The release of 3H]MPP+ was markedly increased by excess KCl (50 mM), acetylcholine (50 microM-10 mM) and by the nicotinic agonists, nicotine (5-100 microM) and 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP, 10-100 microM), but not by the muscarinic agonist, pilocarpine (10-100 microM). Acetylcholine-evoked release of 3H]MPP+ from these cells was mainly mediated by nicotinic receptors: a) nicotine and DMPP stimulated the release of 3H]MPP+, b) a nicotinic antagonist, hexamethonium, markedly blocked the acetylcholine-evoked response and c) pilocarpine was devoid of effect on 3H]MPP+ secretion. At all concentrations tested, somatostatin and octreotide interfered neither with 3H]MPP+ basal release nor with KCl-induced release of 3H]MPP+. However, somatostatin (0.01-0.3 microM) increased the release of 3H]MPP+ induced by a high concentration of acetylcholine (10 mM). Octreotide (1-10 microM) had no effect. These results, showing that somatostatin potentiates acetylcholine-induced 3H]MPP+ release, support the hypothesis that somatostatin may increase the release of catecholamines from adrenal medullary cells.