Abstract
Purpose: :
The aim of the present study was to investigate the role of prostanoids in the inhibitory effect of 8-isoPGE2 on endogenous amino acid neurotransmitter levels in bovine retina, ex vivo.
Methods: :
Freshly isolated bovine eyeballs were equilibrated in oxygenated Krebs buffer solution before being injected intravitreally with either 8-IsoPGE2 or vehicle for control. After 30 minutes of incubation in Krebs buffer solution, retina was isolated and prepared for measurement of glutamate, glutamine and glycine by HPLC-EC. When used, cyclooxygenase (COX) and thromboxane (Tx) synthase inhibitors were intravitreally injected into the eyeballs 15 minutes prior to application of 8-isoPGE2.
Results: :
Intravitreally administered 8-isoPGE2 (0.1 nM - 100 µM) reduced the levels of the excitatory neurotransmitter, glutamate and its metabolite, glutamine and the inhibitory neurotransmitter, glycine in a concentration-dependent manner in bovine retina, ex vivo, yielding IC35 values of 1.5 µM, 5.0 µM and 100 µM, respectively. The non-selective COX inhibitor, flurbiprofen and COX-2 selective inhibitor, NS-398 had no significant effect (p>0.05) on the endogenous levels of glutamate, glutamine, and glycine in bovine retina. Furthermore, flurbiprofen (10 µM) and NS-398 (10 µM) had no effect (P>0.05) on 8-isoPGE2 (0.1 nM - 100 µM)-induced attenuation of glutamate, glutamine and glycine levels. Similarly, the Tx-synthase inhibitor, furegrelate (10 µM) had no effect (P>0.05) on endogenous amino acid levels and did not reverse the isoprostane-induced inhibition of glutamate, glutamine and glycine.
Keywords: neurotransmitters/neurotransmitter systems • retina • receptors: pharmacology/physiology