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Bang V. Bui, Zheng He, James A. Armitage, Christine T. Nguyen, Algis J. Vingrys; Acute and Chronic Blood Pressure Changes Modifies Ocular Susceptibility to Intraocular Pressure Challenge. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5116.
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To consider how acute and chronic blood pressure elevation influences the susceptibility of ocular function and blood flow to acute IOP challenge.
Anaesthetised adult Long-Evan rats with low, normal and high blood pressure underwent a step-wise IOP elevation (10-120 mmHg, 5 mmHg steps every 3 minutes). Acute low (63 ± 2 mmHg, n=6), normal (100 ± 3 mmHg, n=5) and high blood pressure (161 ± 4 mmHg, n=10) was maintained by intravenous infusion of sodium nitroprusside, saline or Angiotensin II, respectively. Chronic hypertension (~180 mmHg, during IOP challenge 161 ± 13 mmHg, n=9) was induced by subcutaneous infusion of Angiotensin II for 4 weeks using an osmotic minipump. The chronic control group had subcutaneous infusion of saline (99 ± 2 mmHg, n=8). During acute IOP elevation, retinal function and ocular blood flow were measured using electroretinography and laser-Doppler Flowmetry, respectively. Susceptibility to IOP challenge was quantified by assessing the IOP that produced 50% attenuation (IOP50%).
Retinal function and ocular blood flow decreased with IOP elevation in all blood pressure groups. Higher BP reduced the susceptibility of retinal function (IOP50% 106 ± 2 mmHg) to IOP challenge, whereas low blood pressure (IOP50% 43 ± 2 mmHg) increased susceptibility compared to the normal blood pressure group (IOP50% 63 ± 4 mmHg). Chronic hypertension also reduced the susceptibility to IOP elevation, however the degree of functional protection was significantly less (~10 mmHg) compared with acute hypertension (P<0.01). This was also true for blood flow (p=0.01). Animals with chronic hypertension developed cardiac hypertrophy and increased aortic wall thickness, without changing baseline retinal function.
Acute hypertension protects both retinal function and blood flow against IOP elevation. This protective effect is reduced in animals with chronic hypertension.
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