ACTIVATION OF ADRENAL-MEDULLARY L-ARGININE - NITRIC-OXIDE PATHWAY BY STIMULI WHICH INDUCE THE RELEASE OF CATECHOLAMINES

The activation of the L-arginine: nitric oxide (NO) pathway in the cat adrenal medulla by different stimuli which induce the release of catecholamines was studied. Stimuli that evoke catecholamine release, such as electrical stimulation of splanchnic nerves (50 V, 5 Hz, 1 ms), methacholine (100 muM), dimethyl-4-phenylpiperazinium iodide (DMPP; 10 muM), high K+ (35 mM) and alamethicin (15 mug ml-1) also caused a rise in cyclic GMP in the perfused cat adrenal medulla. N(G)-nitro-L-arginine methyl ester (L-NAME; 1 mM) abolished the rise in cyclic GMP induced by these stimuli without affecting the catecholamine release. Bovine adrenal medulla cytosol contained an NO synthase which was L-arginine- and Ca2+-dependent. In conclusion cat and bovine adrenal medulla stimulated with a variety of secretagogues synthesize NO from L-arginine to activate the soluble guanylate cyclase. The present data do not rule out a role for cyclic GMP in the regulation of catecholamine secretion; however, it seems more plausible that cyclic GMP may play a role in controlling local blood flow and thus the access of the released catecholamines to the systemic circulation during stressful conflicts.