Effects of Adenosine on the Optic Nerve Head Circulation

Abstract

Abstract: : Purpose: Effects of adenosine on the microcirculation in the optic nerve head (ONH) are presently undetermined, although retinal blood flow has shown to be increased by intravitreal application of adenosine. The purpose of this study is to evaluate whether adenosine is related to the metabolic control for the ONH blood flow. Methods: Capillary blood flow in the optic nerve head was measured by using a laser speckle tissue analyzer every 15 min for 2 hours after intravitreal injection of adenosine (1.0, 10.0 nmol). Mechanisms of adenosine-induced changes were investigated using antagonists and agonists of adenosine receptor subtypes. Results: Intravitreal injection of adenosine increased capillary blood flow in the ONH in a dose dependent way. At a dose of 10 nmol, it amplified the level of capillary blood flow to 235±26.6 % of the baseline. However, intravenous adenosine resulted in no increases to the ONH blood flow. Glibenclamide, a K_ATP channel blocker, suppressed the elevation induced by adenosine (10 nmol) (P=0.001, ANOVA), while 8-bromo-cAMP failed to enhance the capillary blood flow in the ONH. DPCPX, an adenosine A1 receptor blocker also suppressed this increase (P=0.006, ANOVA). Both adenosine A1 and A2a agonists mimiced the effects of adenosine on capillary blood flow . Conclusions: At the capillary level of ONH circulation, adenosine is considered to activate K_ATP channel of pericytes and dilate microvessels. Both A1 and A2a receptors produce adenosine-induced activation of K_ATP channel. Interaction between subtypes of adenosine receptors will be discussed.

Keywords: adenosine • optic disc • laser