Hydrogen sulfide is synthesized endogenously in both retinal artery and retina mostly via CSE.

Hydrogen sulfide (HS) is an important gasotransmitter expressed in various tissues of the organism, including the eye. It is known that HS is localized especially in the retina and corneal layers in bovine eye. The enzymes that mediate HS synthesis are 3-mercaptopyruvate sulfurtransferase (3-MST), cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE). Herein, we aimed to investigate the concentration levels and distribution profiles of these enzymes in bovine retina and retinal artery. Enzyme levels were measured by ELISA and distribution were determined by immunofluorescence microscopic analysis. Much higher concentrations of CBS and CSE have been detected in the retinal artery compared to the retina. In both tissues, particulary 3-MST was found at the lowest level while, CSE was determined to be the most abundant enzyme among the others. CBS distribution was shown in both endothelial and smooth muscle layers, while CSE was seen especially in the endothelial layer of the retinal artery. In the retina, CBS and CSE were expressed in cone-basil cells and retinal ganglion cells, while CSE was also present in bipolar cells. Our results indicated that HS is synthesized endogenously in ocular tissues. The widespread expression of HS synthesizing enzymes in the retina and retinal artery of the bovine eye, which has anatomical similarities with the human eye, may suggest a protective role for HS against retinal vascular diseases as well as a regulatory role in the retinal vascular tone.