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Justin M. Wanek, Pang-yu Teng, Norman P. Blair, Mahnaz Shahidi; A New Imaging Method for Assessment of Inner Retinal Oxygen Consumption in Rat. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1348.
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Normal retinal function requires well regulated metabolism of oxygen and glucose. Since the metabolic activity of the retina may be affected by altered physiological states and/or pathological conditions, methods for assessment of retinal oxygen consumption are needed. The purpose of this study is to report a technique to measure inner retinal oxygen consumption (Q) in rat by combined measurements of oxygen tension (PO2) and capillary blood flow (BF).
PO2 of feeding arteries and draining veins of retinal capillaries were measured using our established phosphorescence lifetime imaging system. PO2 measurements were converted to oxygen saturation (SO2) using the rat hemoglobin dissociation curve and the arteriovenous oxygen content difference was calculated. Capillary blood velocity (BV) was measured by imaging the movement of fluorescent microspheres using a slitlamp biomicroscope equipped with a CCD camera. Capillary BF was derived from BV measurements and the estimated capillary cross-sectional area. Oxygen extraction was determined as the product of BF and arteriovenous oxygen content difference, based on Fick’s principle. Q was then calculated by approximating the volume of inner retinal tissue supplied by the capillary. Repeated measurements were obtained in 5 anesthetized rats under a spontaneous air breathing condition.
In each rat, 3 retinal arterial and venous PO2 measurements and 2 to 6 retinal capillary BV measurements were averaged. Based on data from all rats, PO2 of the feeding retinal arteries and draining veins were 47 ± 7 and 31 ± 6 mmHg (mean ± SD; N = 5), respectively. SO2 of the feeding retinal arteries and draining veins were 59 ± 9% and 33 ± 10% (N = 5), respectively. PO2 and SO2 measurements were significantly higher in feeding arteries as compared to those in draining veins (p<0.005; N = 5). Arteriovenous oxygen content difference was 5.6 ± 2.5 mlO2/100 cc (N = 5). Capillary BV and BF were 2.0 ± 0.1 mm/s and 2.4 ± 0.2 x 10-6 cc/min (N = 5), respectively. Inner retinal oxygen extraction was 1.3 ± 0.5 x 10-7 mlO2/min and Q was estimated to be 2.0 ± 0.9 mlO2/min 100 g (N = 5).
A new method was established for assessment of inner retinal oxygen consumption, which is of value for studying retinal oxygen metabolism under normal, physiologically altered, and experimentally induced pathological conditions in animals.
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