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Abstract
PURPOSE: Ocular tissues contain renin and ocular fluids contain prorenin in amounts that are too high to be explained by admixture with blood or diffusion from blood. It was the purpose of the present study to obtain further evidence for the presence of a local renin-angiotensin system (RAS) in the eye. METHODS: The authors measured the concentrations of angiotensins I and II (ANG I and II) in vitreous fluid and ocular tissues of anesthetized pigs and in human aqueous, vitreous, and subretinal fluid obtained during eye surgery. RESULTS: In tissues obtained from normal porcine eyes (anterior uveal tract, neural retina, retinal pigment epithelium + choroid), ANG I and II were 5- to 100-fold higher than could be accounted for by contamination with blood. ANG I and II in ocular tissues are therefore unlikely to be derived from the circulation. In porcine vitreous fluid, ANG I and II were close to the limit of detection. In addition, during a 2-hour infusion of 125I-ANG I in the rabbit, 125I-ANG I in vitreous fluid reached a level only 1% of the level in arterial plasma. Thus, in the presence of an intact blood-retinal barrier, little or no ANG I or II enters the vitreous compartment. In human ocular fluids obtained from diseased eyes, ANG I and II levels were readily measurable and correlated linearly with the level of serum albumin, indicating that after partial breakdown of the BRB, diffusion of ANG I and II from the circulation into the eye may occur. CONCLUSION: Results indicate that both ANG I and II are generated locally in ocular tissues with little leakage into ocular fluids. These findings, together with previously published data on renin and prorenin, show a high degree of compartmentalization of the RAS in the eye and are in agreement with similar findings in other tissues, where there is evidence for the existence of a local RAS.