[Constitutional release of nitrogen monoxide (NO) by the retina of the minipig is a major determinant of arteriolar basic tonus in the internal retina]

NO is a nonpolar gas, which diffuses across cell membranes in an isotropic fashion. In relatively large arteries NO has been identified as the endothelium-derived releasing factor and the current hypothesis is that NO controls the vascular tone. We are investigating an alternative hypothesis proposing that the retinal tissues surrounding the arterioles contribute in the process of NO production.We performed flicker light stimulation in anesthetized minipigs (hypnodyl 100 mg/hr, tubocurarine 0.1 mg/hr und N2O) in steady-state of normoxia-normocapnia. An NO-microprobe mounted on a micromanipulator was introduced into the eye through the pars plana and positioned on the preretinal space in a zone free of visible vessels. Preretinal NO gradient and recording of NO release variations in response to flicker light stimulation were performed so as periarteriolar microinjections of nitro-L-arginine.When advancing the NO-probe from the vitreous towards the retina we recorded an NO-gradient corresponding to an efflux of 7.1 pMol x min-1 x cm-2 (N = 9). With the microprobe positioned close to the retina and after 60 min dark adaptation we recorded a mean increase in NO release of 1.59 muMol +/- 0.13 SE. After periarteriolar microinjection of nitro-Larginine we recorded a transitory reversible vasoconstriction.These results indicate that a process occurring in the extravascular tissue of the retina modulates the production of NO and that constitutional NO release by the retina is a major determinant of the basal retinal arteriolar tone.