Effects of adenosine on optic nerve head circulation in rabbits

This study was performed to determine whether intravitreal or intravenous adenosine can alter the microcirculation in the optic nerve head (ONH) of rabbits. Capillary blood flow in the ONH was measured serially with a laser speckle tissue analyser for 2 hr after the intravitreal (0·1, 1·0 and 10 nmol) or intravenous (0·2 and 0·6 mg kg −1 min) injections of adenosine. In addition, the effect of specific adenosine A 1 and A 2a antagonists and an adenosine triphosphate (ATP)-sensitive potassium (K ATP) channel blockers on the adenosine-induced changes on the ONH blood flow was analysed. Intravitreal adenosine increased the capillary blood flow in the ONH in a dose-dependent manner, while intravenous adenosine had no effect. Co-administration of the specific adenosine A 1 receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 10 nmol) significantly suppressed ( P=0·006, ANOVA) the increase in the ONH blood flow induced by adenosine (10 nmol). The specific A 2a receptor antagonist, 8-(3-chlorostyryl) caffeine (CSC, 10 nmol), had a weak effect in inhibiting the increase but the change was not significant ( P=0·08, ANOVA). Both specific A 1 and A 2a receptor agonists, N 6-cyclopentyladenosine (CPA, 10 nmol) and 2- p-(2-carboxyethyl) phenethyl-amino-5′- N-ethylcarboxamidoadenosine (CGS-21680, 10 nmol), increased the ONH tissue blood flow ( P