ROLE OF PROSTAGLANDINS AND ACETYLCHOLINE IN THE CONTRACTILE ACTIONS OF HYDROGEN SULFIDE-RELEASING COMPOUNDS IN THE BOVINE ISOLATED IRIS

Abstract

Purpose : Previously, we reported that hydrogen sulfide (H₂S)-releasing compounds can relax pre-contracted porcine isolated irides, an effect that was dependent upon endogenous production of both H₂S and prostaglandins, and on the activity of K_ATP channels (Ohia et al. Curr. Eye Res. 35: 402, 2010). In the present study, we investigate the pharmacological actions of H₂S-releasing compounds (NaHS and L-cysteine) on basal tone in bovine isolated irides. Furthermore, we studied role of prostaglandins and acetylcholine in the responses elicited by the H₂S-releasing compounds on this tissue.

Methods : Isolated bovine iris muscle strips were set up in an organ baths 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. Contractile responses were elicited by the H₂S releasing compounds in the absence and presence cyclooxygenase (COX) inhibitors (flurbiprofen and indomethacin) or the muscarinic receptor blocker, atropine.

Results :
NaHS (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. Likewise, atropine (1 nM – 10 nM) significantly (p < 0.001) antagonized the contractile response to NaHS and L-cysteine.

Conclusions : We conclude that H₂S-releasing compounds can elicit contraction of isolated bovine irides, an effect that is dependent upon the production of endogenous prostaglandins and the release of acetylcholine.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.