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M. Pouliot, M. C. Deschênes, S. Hétu, S. Chemtob, M. R. Lesk, R. Couture, E. Vaucher; Quantitative Measurement of Blood Flow in the Retina of Rats by Autoradiography Using [14C]-IMP. Invest. Ophthalmol. Vis. Sci. 2009;50(13):405.
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Quantitative and regional measurement of retinal blood flow in rodents is of prime interest for the investigation of regulatory mechanisms of ocular circulation in physiological and pathological conditions. In this study, a new quantitative autoradiographic method using N-isopropyl-p-14C-iodoamphetamine ([14C]-IMP), a diffusible radioactive tracer, was evaluated for its ability to detect changes in retinal blood perfusion during hypercapnia. Findings were compared to cerebral blood flow values measured simultaneously.
Hypercapnia was induced in awake Wistar rats by inhalation of 5% or 8% CO2 in medical air. Five minutes later, 100 µCi/kg [14C]-IMP was injected in the femoral vein within 30s. Two minutes later, the brain was frozen, the eyes were enucleated and both retinas were dissected out. One retina was digested and the amount of total radioactivity was determined with a scintillation counter. The other retina was whole-mounted on a glass slide and exposed with 20-micron thick brain sections on X-ray film for the quantification of regional changes in four retinal quadrants (nasal, temporal, superior and inferior) with computerized analysis (MCID basic 7.0).
Retinal and cerebral blood flow were significantly increased under hypercapnic conditions. Autoradiographic analysis showed that retinal blood flow increased in every quadrants examined by 23 to 42%.
These results showed that hypercapnia-induced increase in retinal blood flow can be quantified using [14C]-IMP autoradiographic method and compared with brain changes. Therefore, this technique is a powerful tool to study how retinal blood flow is regulated in different regions of the rat retina.
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