Intraocular pressure and vascular effects of sodium azide in bovine perfused eye

The effects of the nitrovasodilator, sodium azide, on intraocular pressure (IOP) and ciliary vascular tone were compared. IOP was measured in the bovi ne isolated eye that was perfused via the ciliary artery. Separately, vasod ilator effects were assessed after raising the vascular tone using noradren aline (10 muM). Aqueous humor formation (AHF) rate was estimated by a fluor escein dilution method. Cyclic GMP in the ciliary processes was measured by radioimmunoassay. When compared with controls, sodium azide (10 nmole bolus dose) was found t o lower IOP (2.2 +/- 0.3 mm Hg; P < 0.01) via a reduction in AHF (12.19 +/- 0.26 mul/min to 6.36 +/- 0.53 mul/min; P < 0.001). Azide (1 mu mole) also reduced ciliary vascular resistance (81.0 +/- 5.5%; P < 0.01). However, the drug was 20x more potent as an ocular hypotensive than as a vasodilator (E D50 0.28 nmole on IOP, 5.55 nmole on vascular effect). Azide (10 nmole) als o increased levels of ciliary cyclic GMP (127 +/- 17 fmol/mg protein to 233 +/- 27 fmol/mg protein, P < 0.01). The IOP-lowering effect of azide does not appear to depend on its ability t o activate guanylyl cyclase (GC) in vascular smooth muscle, but rather is l ikely a consequence of direct activation of ciliary epithelial GC.