We have previously reported that hydrogen sulfide (H2S) donors can relax pre‐contracted, porcine isolated irides, an effect that was dependent upon endogenous production of H2S and prostaglandins, and on the activity of KATP channels (Ohia et al. Curr. Eye Res. 35: 402, 2010). In the present study, we examined the pharmacological actions of H2S donors (NaHS and L‐cysteine) on basal tone in bovine isolated irides. Furthermore, we studied the effect of inhibition of cyclo‐oxygenase (COX) on this response.MethodsIsolated bovine iris muscle strips were set up in an organ bath containing oxygenated Krebs buffer solution maintained at 37°C and gassed with 95% O2: 5% CO2. The muscle strips were set to a resting tension of 0.3 g and longitudinal isometric tension was recorded via a Grass FT03 force‐displacement transducer and analyzed using PolyView Computer Software.ResultsNaHS (1 nM – 10 μM) and L‐cysteine (100 nM – 1 mM) caused a concentration‐dependent contraction of isolated bovine irides yielding EC50 values of 10 nM and 30 μM, respectively. Both COX inhibitors, flurbiprofen (10 μM) and indomethacin (10 μM) abolished the contractile actions of NaHS and L‐cysteine on this tissue.ConclusionsWe conclude that H2S donors can elicit contraction of isolated bovine irides, an effect that is dependent upon the production of endogenous prostaglandins. Based on data reported previously in the porcine isolated irides in which L‐cysteine had no direct contractile action on this tissue, the present finding that L‐cysteine can elicit contractions of bovine isolated irides indicates that a species difference exists in the response of mammalian irides to exogenously applied H2S donors.