Intraocular adenosine levels in normal and ocular-hypertensive patients.

Abstract

Adenosine receptors modulate several ocular responses; however, our understanding of factors that influence ocular extracellular adenosine levels is limited. The objective of this study was to evaluate how changes in intraocular pressure (IOP) influence endogenous levels of the purines adenosine and inosine, in the aqueous humor of normal and ocular-hypertensive patients. Informed consent was obtained from 51 individuals undergoing cataract extraction or glaucoma surgical procedures. IOP was measured immediately prior to surgery. At the start of the surgical procedure, an aqueous sample of 75-100 microL was obtained. Purine levels were determined by reverse-phase HPLC. In normotensive individuals, mean aqueous adenosine and inosine levels were 5.2 +/- 1.1 and 19.4 +/- 2.2 ng/100 microL, respectively. No significant correlation between IOP and purine concentration was measured in this group. In ocular hypertensive individuals, the mean aqueous adenosine and inosine concentration was significantly elevated when compared to normotensive individuals. In the ocular hypertensive individual, this elevation in adenosine level was significantly correlated with IOP (r(2) = 0.42). These results demonstrate that in ocular hypertensive individuals, aqueous adenosine concentration is correlated with IOP. As the activation of adenosine receptors can modulate IOP and retinal blood flow, adenosine release during periods of ocular hypertension may play an important role in the physiological responses to elevated IOP.