Oxygen consumption in the avascular guinea pig retina

Oxygen consumption across the retina of a mammal with a naturally avascular retina has not previously been investigated. The oxygen consumption across the avascular retina of the guinea pig was measured in vivo by spatial analysis of the intraretinal oxygen profile. The avascular nature of the guinea pig retina allows the inner retina to be included in the analysis without disrupting the normal physiological state of the retina. Oxygen-sensitive microelectrodes (1-mu m tip) were used to make high-resolution measurements of oxygen tension through the retina of anesthetized, mechanically ventilated guinea pigs (n = 10). Oxygen profiles were then analyzed in terms of oxygen tension as a function of distance from the choriocapillaris/Bruch's membrane, and the data were fitted to an established mathematical model of retinal oxygen consumption. The average oxygen consumption of the full thickness of the guinea pig retina was 1.1 +/- 0.09 ml O-2 . min(-1). 100 g(-1) (n = 10). The average oxygen consumption of the outer half of the retina was 2.07 +/- 0.17 ml O-2 . min(-1). 100 g(-1), while that of the inner half was only 0.12 +/- 0.04 ml O-2 . min(-1). 100 g(-1). A localized region of high oxygen consumption was identified in the outer retina in every case, and this region accounted for an average of 93.9 +/- 2.0% of the total retinal oxygen consumption. Only 5.2 +/- 1.4% of the total oxygen consumption was attributable to the inner half of the retina. When choroidal oxygen tension was increased via a combination of systemic hyperoxia and hypercapnia, high oxygen levels could be sustained in all retinal layers. Under these conditions of an excess oxygen supply, the inner retina still consumed only 0.45 +/- 0.11 ml O-2 . min(-1). 100 g(-1), which was 13.8 +/- 2.5% of the total retinal oxygen consumed. The relatively low oxygen consumption in the inner retina of the guinea pig may reflect an interesting adaptation to the constraints imposed by the absence of a retinal circulation in this species.