0169 : Effects of intermittent hypoxia on rat ophthalmic artery reactivity: role of endothelin 1, oxidative stress and endothelium derived hyperpolarizing factors

Abstract

Obstructive sleep apnea (OSA) is a common disease, characterized by recurrent desaturation-reoxygenation sequences. Intermittent hypoxia (IH) has been proposed as major component of OSA. OSA has been recently associated with a higher frequency of optic neuropathies. There are currently no pathophysiological data regarding the effect of HI or OSA on ocular vascular system. This study aims to characterize IH impact on rat ophthalmic artery (OA) reactivity. Particularly, the role of endothelin 1 (ET-1), oxidative stress and endothelium derived hyperpolarizing factors (EDHF) were studied. Rats were exposed to 14 days IH (IH rats) or normoxia (NX rats). Ophthalmic artery reactivity was studied using wire myography. Endothelin A receptor (ETRA) expression and superoxide anions production in OA were studied by immunohistolabelling and DHE labelling respectively. After 14 days IH, ETRA immunolabeling and superoxide anions expression in OA were increased by 22% (p = 0.015) and 23% (p = 0.04) respectively in IH rats. Ophthalmic artery contraction to 3.10-8 M ET-1 was increased by 16% (p<0.05) in IH rats. ETRA blockage (BQ-123) almost completely abolished contractile response to ET-1 in both groups. Endothelin B receptor (ETRB) blockage (BQ-788) increased response to ET-1 in NX rats but not in IH rats. Relaxation to acetylcholine (Ach) was significantly delayed in IH rats (p<0.0001). After NOS blockade with L-NAME, difference in Ach induced relaxation between groups was abolished. Cytochrome P450 inhibition by fluconazole had an opposite effect on response to Ach in NX and IH rats, increasing relaxation to Ach in IH rats and delaying it in NX rats. 14-day IH-exposure induces endothelial dysfunction in rat ophtalmic artery, associated with increase in oxidative stress and change in EDHF contribution to endothelial function. The increased contractile response to ET-1 in IH rats was due to an increase in ETRA -vasoconstriction and a decrease in ETRB vasorelaxation. The author hereby declares no conflict of interest