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 cate cholamines was studied. Stimuli that evoke catecholamine release, such as electrical stimulation of splanchnic nerves (50 V, 5 Hz, 1 ms), me thacholine (100 muM), dimethyl-4-phenylpiperazinium iodide (DMPP; 10 m uM), 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-argini ne methyl ester (L-NAME; 1 mM) abolished the rise in cyclic GMP induce d 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 sti mulated with a variety of secretagogues synthesize NO from L-arginine to activate the soluble guanylate cyclase. The present data do not rul e out a role for cyclic GMP in the regulation of catecholamine secreti on; however, it seems more plausible that cyclic GMP may play a role i n controlling local blood flow and thus the access of the released cat echolamines to the systemic circulation during stressful conflicts.