Angiotensin Converting Enzyme System in the Normal Canine Eye: Pharmacological and Physiological Aspects

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Abstract
The function of the renin-angiotensin-aldosterone system (RAAS) in the mammalian eye remains unclear, although alterations in the concentrations of various pathway components can influence intraocular pressure and the electroretinogram. Angiotensin Converting Enzyme (ACE) has been localized to ocular tissues and fluids. Aqueous humor and serum values of ACE are increased in sarcoid uveitis patients. We used the dog to simultaneously examine the effects of a topically administered ACE inhibitor on the intraocular pressure (IOP), on components of the renin-angiotensin pathway in the serum and aqueous humor, and to monitor any systemic effects of the ACE inhibitor. The novel ACE inhibitor, SCH 33861 (Schering Corporation), decreased IOP in amounts similar to timolol when applied topically to the canine eye. Serum ACE values significantly decreased in SCH 33861 treated dogs, while aqueous ACE values were only slightly decreased. A decrease in heart rate, and systolic and diastolic blood pressure in these dogs during the treatment period indicated probable systemic absorption. Normal values of aqueous humor and serum angiotensin-I were established for the dog. Plasma renin activity and angiotensin-I values were not significantly changed for any of the treatment groups. Topical application of SCH 33861 to the canine eye is a useful model to further evaluate the role of the renin-angiotensin system in the eye.