Intraocular pressure lowering by S-allylmercaptocysteine in rabbits

The purpose of this study was to examine the actions of a garlic-derived co mpound, S-allylmercaptocysteine (SAMC) on intraocular pressure (IOP) and to determine the possible involvement of sulfhydryl reactivity, sympathetic n euronal activity and atrial natriuretic peptide (ANP) in the IOP response. Topical, unilateral application of SAMC (20, 100, 200 mu g) elicited dose-d ependent decreases in IOP. The magnitude of the IOP-lowering effect induced by SAMC was between four to six mmHg. The ocular hypotensive responses wer e unilateral, peaked at one to three hours and lasted from two to four hour s. The IOP-lowering effect by SAMC (100 mu g) was enhanced modestly by topi cal, bilateral pretreatment with a reducing agent, tris(2-carboxyethyl) pho sphine (100 mu g) which itself produced no change in IOP. No alteration of pupil diameter was observed following topical application of either SAMC or tris(2-carboxyethyl) phosphine. Thus, alteration of sulfhydryl reactivity does not seem to be a major mechanism of action for SAMC. SAMC caused no ch ange of basal and electrically stimulated norepinephrine release in rabbit iris-ciliary bodies, ruling out a prejunctional effect on sympathetic nerve activity. However, SAMC increased the ANP levels in aqueous humor by five- fold. It is concluded that the ocular hypotensive response induced by SAMC in rabbits could involve the elevation of ANP levels in aqueous humor.