ACTIONS OF S-NITROSOCYSTEINE IN THE NUCLEUS-TRACTUS-SOLITARII ARE UNRELATED TO RELEASE OF NITRIC-OXIDE

Cardiovascular effects elicited by microinjection of L-S-nitrosocystei ne in the nucleus tractus solitarii (NTS) were compared and contrasted with those produced by the dextroisomer, other nitric oxide donors an d nitric oxide itself. L-S-nitrosocysteine produced dose-related decre ases of arterial pressure and heart rate. In contrast, D-S-nitrosocyst eine, S-nitrosoglutathione, glyceryl trinitrate, and sodium nitropruss ide produced minimal responses that were not dose-related. Likewise, i njection of cystine and nitric oxide, two products of S-nitrosocystein e breakdown, produced no significant response. Headspace analysis usin g chemiluminescence revealed that L- and D-S-nitrosocysteine released identical amounts of nitric oxide when exposed to homogenates of whole rat brain. Responses to L-S-nitrosocysteine were not affected by loca l injection of oxyhemoglobin or the nitric;pride synthase inhibitor L- nitroarginine methylester. Although injection of L-cysteine into the N TS produced responses similar to those seen with injection of L-S-nitr osocysteine, blockade of excitatory amino acid receptors with kynureni c acid inhibited responses to cysteine but not those to the nitrosothi ol. The study demonstrates that S-nitrosocysteine is biologically acti ve in the NTS. Its action is independent of release of nitric oxide fr om the nitrosothiol but may be mediated through stereoselective sites on tar et neurons.