Abstract
Purpose: :
To consider how acute and chronic blood pressure elevation influences the susceptibility of ocular function and blood flow to acute IOP challenge.
Methods: :
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%).
Results: :
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.
Conclusions: :
Acute hypertension protects both retinal function and blood flow against IOP elevation. This protective effect is reduced in animals with chronic hypertension.
Keywords: electroretinography: non-clinical • blood supply • intraocular pressure