THE EFFECTS OF INTRAVITREALLY INJECTED ENDOTHELIN-1 ON THE IRIS-CILIARY BODY MICROVASCULATURE IN RABBITS

Purpose. We previously reported that intravitreal injection of 0.5 mu g of endothelin-1 (ET-1) caused both a sustained reduction of intraocu lar pressure (IOP) and decreased aqueous production in the rabbit eye. On the theory that these effects might have resulted from a sustained reduction of blood flow to the ciliary body due to ET-1-mediated vaso constriction, in the present study we attempted to determine if ET-1 c auses any changes in the vascular caliber of the iris-ciliary body. Me thods. ET-1 solution (0.5 g mu) was injected into the vitreous of one eye of each of 10 albino rabbits; the same amount of vehicle was injec ted into the contralateral eyes. One h following these injections in f ive of the rabbits and 24 h following them in the other five rabbits, ocular microvascular castings were obtained under controlled physiolog ic conditions, and the amount of vasoconstriction of the arterioles br anching from the major arterial circle of the iris (MAC) and supplying the iris-ciliary body was measured by a scanning electron microscope and expressed as a percentage. Results. The ET-1 caused a statisticall y significant focal vasoconstriction in the treated eyes as compared w ith the contralateral, control eyes (9.9% at 1 h and 6.2% at 24 h; bot h P = .0001). Conclusions. Intravitreally injected ET-1 caused statist ically significant, but only mild vasoconstriction of the arterioles s upplying the ciliary processes.