Remote ischemia influences the responsiveness of the retina: observations in the rat

Abstract

Purpose: Remote ischemic preconditioning (RIP) has been found to be protective of heart and brain against ischemic injury. We have tested the effects of RIP on retinal function using the electroretinogram.

Methods: Ischemia remote from the retina was induced in one hindlimb, using a pressure cuff applied for between 5 and 10 minutes. A temperature probe on the footpad confirmed blockage of the circulation. To test the impact of RIP on retinal function, we recorded the dark-adapted flash electroretinogram (ERG) in four groups (n = 5 per group) of Sprague-Dawley rats (sham, 5-minute, 10-minute, and 2 × 5-minute ischemia). Heart rate, breath rate, and peripheral oxygen saturation were monitored using infrared pulse oximetry.

Results: RIP increased both the a- and b-waves by up to 14%, more markedly after the longer periods (10 minutes or 2 × 5 minutes) of ischemia. The effect was tested up to 30 minutes after ischemia and retested at 1 week and 1 month. RIP did not appear to accelerate the initial stages of recovery from photopigment bleach. Systemic oxygen saturation, heart rate, and respiration did not vary consistently during or after remote ischemia.

Conclusions: The effect of RIP on the ERG is a novel finding. Possible mechanisms of this effect are discussed and related to the idea of neuroprotection and to fundamentals of the electroretinogram.

Keywords: ATP-sensitive potassium channel; adenosine; dark adaptation; electroretinogram; remote ischemic preconditioning; retina.