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Grant Cull, Lin Wang, Hui Li, Bang V Bui; The effect of ocular perfusion pressure lowering on vessel diameter and astrocyte calcium in the rat retina.. Invest. Ophthalmol. Vis. Sci. 2016;57(12):3001.
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© ARVO (1962-2015); The Authors (2016-present)
To test that lowering ocular perfusion pressure (OPP) by reducing blood pressure (BP) causes parallel changes in arterial astrocyte calcium levels (Ca2+) and vessel diameter (Ø) within the rat retina.
In 17 rats, femoral vein and arteries were surgically cannulated. In the Ca2+ group (n=8), 5 μl Fluo-4 AM solution was injected intravitreally in both eyes. To establish Ca2+ baseline (BL), three 30-second cSLO image sequences, in fluorescein mode were acquired. In the Ø group (n=9), BL diameter was acquired with the cSLO in infrared reflection mode. A syringe pump withdrew blood (1ml/min) via a femoral artery to induce a slow constant decrease in BP. One minute image sequences were acquired for both groups every 1.7 minutes until BP was < 30 mmHg. Ca2+ level and Ø were analyzed offline using ImageJ. The images for each test were combined into one stack, registered and analyzed across all time points. The Ca2+ intensity and Ø were measured one disc diameter from the optic nerve. Change in Ca2+ and Ø for each artery was expressed relative to its own BL (%). Statistical analysis was performed using repeated measures ANOVA, with a post hoc comparison (Dunnetts test). Analysis of covariance compared the differences of BP change over time between the Ca2+ and Ø groups.
: Baseline BP and its change over time was not significantly different between the 2 groups (p=0.56). The average BL BP was 84.1 ± 7.6 mmHg (n=17). With blood withdrawal BP decreased at a rate of 4.6 ± 0.8 mmHg/min (SD) to reach 30 mmHg in 13.2 ± 2.9 minutes. In the Ca2+ group a significant increase (p=0.01) in Ca2+ from BL was observed for BP reductions of 54 mmHg or more (p<0.001). There was no significant change in Ø from baseline as BP declined. However once BP was < 34 mmHg the arteries were constricted.
Lowering BP caused an increase in periarterial astrocytes Ca2+ with no equivalent change in arterial Ø. This suggests that astrocyte may be involved in maintaining the arterial Ø as BP declines and play a role in blood flow regulation in the rat retina. Further studies are required to correlate the function of astrocytes with blood flow regulation.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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