Mean responses to (a) nitric oxide gas solution (NO; 1 μM; n=4 – 6), (b) Angeli's salt (1 μM; n=4), (c) acetylcholine (ACh; 0.3 μM n=4), (d) sodium nitroprusside (SNP; 0.03 μM; n=4), (e) glyceryl trinitrate (GTN; 0.1 μM; n=4 – 6 (f) spermine NONOate (SperNO; 1 μM; n=3 – 4) on mouse aortae in the absence (control) and presence (treated) of carboxy-PTIO (c-PTIO; 100 μM), hydroxocobalamin (HC; 100 μM) or L-cysteine (3 mM); pre-incubation time 3 min. Relaxation responses are expressed as per cent reversal of the phenylephrine-induced contraction. Responses to Angeli's salt in the presence of inhibitors have been corrected for the time-related reduction in responses to this agent seen in the absence of inhibitors, using the correction factor referred to in the Methods. Points are mean values with s.e.mean shown by vertical bars. *0.05>P>0.01, **0.01>P>0.001, ***P<0.001 when compared with corresponding control value.