S-NITROSOTHIOLS AND THE NITRERGIC NEUROTRANSMITTER IN THE RAT GASTRICFUNDUS - EFFECT OF ANTIOXIDANTS AND METAL CHELATION

1 The effects of the antioxidants ascorbic acid and alpha-tocopherol a nd of the metal chelator ethylenediaminetetraacetic acid (EDTA) were s tudied on relaxations in response to S-nitrosothiols, authentic nitric oxide (NO) and nitrergic non-adrenergic non-cholinergic stimulation o f the rat gastric fundus. 2 The S-nitrosothiols S-nitrosocysteine (1-1 00 nM), S-nitrosoglutathione (0.01-3 mu M) and S-nitroso-N-acetylpenic illamine (0.01-3 mu M) induced concentration-dependent relaxations of the rat gastric fundus muscle strips, which were precontracted with pr ostaglandin F-2 alpha. The relaxations to all S-nitrosothiols were con centration-dependently enhanced by the antioxidants ascorbic acid (0.1 -3 mu M) and alpha-tocopherol (3-30 mu M) and inhibited by the metal c helator EDTA (26 mu M). 3 Ascorbic acid and alpha-tocopherol alone did not induce a relaxation of the precontracted rat gastric fundus muscl e strip. However, when ascorbic acid (1 mu M) or alpha-tocopherol (1 m u M) were injected in the organ bath 1 minute after S-nitrosoglutathio ne (0.1 mu M) or after S-nitroso-N-acetylpenidllamine (0.1 mu M), they induced an immediate, sharp and transient relaxation. This relaxation was inhibited by the superoxide generator pyrogallol (2 mu M). Such a relaxation to ascorbic acid or a-tocopherol was not observed in the p resence of S-nitrosocysteine (10 nM). 4 Electrical held stimulation (0 .5-4 Hz) of the precontracted rat gastric fundus strips induced freque ncy-dependent nitrergic relaxations which were mimicked by authentic N O (3-300 nM) and by acidified sodium nitrite NaNO2 (0.3-10 mu M). Asco rbic acid (0.3-3 mu M), alpha-tocopherol (3-30 mu M) or EDTA (26 mu M) did not affect the relaxations to nitrergic stimulation, NO or NaNO2. 5 In summary, relaxations to S-nitrosothiols in the rat gastric fundu s are enhanced by the antioxidants ascorbic acid and alpha-tocopherol and inhibited by the metal chelator EDTA. However, relaxations to nitr ergic stimulation of the rat gastric fundus or those to authentic NO w ere not affected by the antioxidants or by the metal chelator. These r esults indicate that antioxidants and metal chelators have a different effect on the biological activity of S-nitrosothiols and on that of t he nitrergic neurotransmitter. Therefore, our results suggest that S-n itrosothiols do not act as intermediate compounds in nitrergic neurotr ansmission in the rat gastric fundus.