ANGIOTENSIN LEVELS IN THE EYE

Purpose. Ocular tissues contain renin and ocular fluids contain proren in in amounts that are too high to be explained by admixture with bloo d 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 concentrati ons of angiotensins I and II (ANG I and II) in vitreous fluid and ocul ar tissues of anesthetized pigs and in human aqueous, vitreous, and su bretinal fluid obtained during eye surgery. Results. In tissues obtain ed from normal porcine eyes (anterior uveal tract, neural retina, reti nal pigment epithelium + choroid), ANG I and II were 5- to 100-fold hi gher than could be accounted for by contamination with blood. ANG I an d II in ocular tissues are therefore unlikely to be derived from the c irculation. In porcine vitreous fluid, ANG I and II were close to the limit of detection. In addition, during a 2-hour infusion of I-125-ANG I in the rabbit, I-125-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 co mpartment. In human ocular fluids obtained from diseased eyes, ANG I a nd 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 generat ed locally in ocular tissues with little leakage into ocular fluids. T hese findings, together with previously published data on renin and pr orenin, show a high degree of compartmentalization of the RAS in the e ye and are in agreement with similar findings in other tissues, where there is evidence for the existence of a local RAS.