Abstract
Purpose :
The retinal vascular system is devoid of autonomic nervous supply and therefore retinal blood flow is autoregulated. However, it is unknown to what extent electrical activity in the retina during the visual process contributes to this flow regulation. The purpose of the present study was to study changes in vascular tone in retinal arterioles during electrical field stimulation (EFS) and in the presence of veratridine, simulating neuronal activity around the vessels.
Methods :
Porcine ciliary arteries and retinal arterioles were mounted in a myograph system and the tone was measured during: A) Six series of bipolar field stimulations with a frequency of 1 Hz successively doubled to reach 32 Hz. In each series 30 mA pulses with a duration of 0.3 msec were applied during 20 sec, followed by a resting period of 5 min. B) The successive addition of the Na+ channel opener veratridine in the concentrations: 10-6, 3x10-6, 10-5 and 3x10-5 M. The experiments were repeated after addition of the Na+ blocker tetrodotoxin (TTX). The effect of veratridine was furthermore investigated in the presence of the COX-blocker, ibuprofen (10-5 M), NOS-blocker, L-NAME (10-4 M) and the adenosine-receptor-blocker, 8-PSPT (5x10-5 M). All experiments were conducted both in isolated and non-isolated vessels.
Results :
EFS had no significant effect on the tone of retinal arterioles (p>0.66), whereas veratridine showed a concentration dependent relaxation of these vessels (p<0.01). The effect was partially reduced by TTX which depended on the presence of perivascular retinal tissue. Neither ibuprofen, L-NAME nor 8-PSPT affected the veratridine induced relaxation compared to the controls. However, when comparing isolated vessels to vessels with preserved perivascular retinal tissue, relaxation was reduced in the ibuprofen and 8-PSPT group at the second highest and two highest veratridine concentrations, respectively.
Conclusions :
EFS has no effect on the tone of porcine retinal arterioles in vitro which may be due to the lack of autonomic nervous supply. The relaxing effect of veratridine does not involve products of cyclo-oxygenase, nitric oxide synthase or the adenosine receptor.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.