Effect of hydrogen sulfide on sympathetic neurotransmission and catecholamine levels in isolated porcine iris-ciliary body.

In the present study, we investigated the pharmacological action of hydrogen sulfide (H2S, using sodium hydrosulfide, NaHS, and/or sodium sulfide, Na2S as donors) on sympathetic neurotransmission from isolated, superfused porcine iris-ciliary bodies. We also examined the effect of H2S on norepinephrine (NE), dopamine and epinephrine concentrations in isolated porcine anterior uvea. Release of [3H]NE was triggered by electrical field stimulation and basal catecholamine concentrations was measured by high performance liquid chromatography (HPLC). Both NaHS and Na2S caused a concentration-dependent inhibition of electrically evoked [3H]NE release from porcine iris-ciliary body without affecting basal [3H]NE efflux. The inhibitory action of H2S donors on NE release was attenuated by aminooxyacetic acid (AOA) and propargyglycine (PAG), inhibitors of cystathionine beta-synthase (CBS) and cystathionine gamma-lyase (CSE), respectively. With the exception of dopamine, NaHS caused a concentration-dependent reduction in endogenous NE and epinephrine concentrations in isolated iris-ciliary bodies. We conclude that H2S can inhibit sympathetic neurotransmission from isolated porcine anterior uvea, an effect that is dependent, at least in part, on intramural biosynthesis of this gas. Furthermore, the observed action of H2S donors on sympathetic transmission may be due to a direct action of this gas on neurotransmitter pools.

Inhibitory action of hydrogen sulfide on muscarinic receptor-induced contraction of isolated porcine irides.

We investigated the pharmacological actions of hydrogen sulfide (H(2)S) using sodium hydrosulfide (NaHS) and sodium sulfide (Na(2)S) as donors on isolated porcine irides in the presence of tone induced by muscarinic receptor stimulation. Furthermore, we also investigated the mechanism of action of H(2)S in this smooth muscle. Isolated porcine iris muscle strips were set up in organ baths and prepared for measurement of longitudinal isometric tension. The relaxant action of NaHS or Na(2)S on carbachol-induced tone was studied in the absence and presence of a K(+)-channel inhibitor and inhibitors/activators of enzymes of the biosynthetic pathways for H(2)S, prostanoid and nitric oxide production. In the concentration range, 10 nM to 100 microM, NaHS produced a concentration-dependent relaxation of carbachol-induced tone reaching a maximum of inhibition of 28% at 30 microM. The cyclooxygenase inhibitor, flurbiprofen (1 microM), enhanced relaxations induced by both NaHS and Na(2)S yielding IC(50) values of 7 microM and 70 microM, respectively. With exception of l-NAME (300 muM) inhibitors of cystathionine gamma-lyase, propargylglycine, (PAG) (1 mM) and beta-cyanoalanine, (BCA) (1 mM) and inhibitors of cystathionine beta-synthase, aminooxyacetic acid (AOA) (30 microM) and hydroxylamine (HOA) (30 microM) caused significant (P < 0.001) rightward shifts in the concentration-response curves to NaHS. An activator of cystathionine beta-synthase, SAM (100 microM), enhanced relaxations elicited by low concentrations of NaHS but attenuated responses caused by the higher concentrations of this H(2)S donor. The inhibitor of K(ATP) channel, glibenclamide (100 and 300 microM), blocked relaxations induced by NaHS. We conclude that the observed inhibitory action of NaHS and Na(2)S in isolated porcine irides is dependent on endogenous production of prostanoids and the biosynthesis of H(2)S by cystathionine gamma-lyase and cystathionine beta-synthase. Furthermore, relaxation induced by H(2)S is mediated, at least in part, by K(ATP) channels. Nitric oxide is not involved in the relaxation induced by this gas in the isolated porcine irides.