Hydroxocobalamin and haemoglobin differentiate between exogenous and neuronal nitric oxide in the rat gastric fundus

In longitudinal strips of rat gastric fundus, hydroxocobalamin (30 microM) significantly reduced relaxations to sodium nitroprusside (100 nM), nitric oxide (NO; 5 microM) and S-nitrosocysteine (3 microM), whereas responses to non-adrenergic, non-cholinergic (NANC) nerve stimulation were only slightly reduced. The stimulation-induced relaxations were markedly reduced by the NO synthase inhibitor NG-nitro-L-arginine (100 microM). Hydroxocobalamin (30 microM) enhanced relaxations to S-nitrosoglutathione (1 and 3 microM), and had no effect on responses to vasoactive intestinal polypeptide (1 nM). Haemoglobin (10 microM) significantly reduced relaxations to sodium nitroprusside, NO, S-nitrosocysteine and S-nitrosoglutathione, but did not affect responses to NANC nerve stimulation or vasoactive intestinal polypeptide. The results suggest that hydroxocobalamin and haemoglobin can differentiate between exogenous and neuronally released NO, and that the transmitter released from nitrergic nerves in the rat gastric fundus is not free NO or the nitrosothiols, S-nitrosocysteine and S-nitrosoglutathione.