The Upright Body Position Increases Translaminar Pressure Gradient in Normotensive and Hypertensive Rats

Abstract

ABSTRACTAim: Several lines of evidence suggest that the pathogenesis of glaucoma may depend on an increased translaminar pressure gradient (TPG), the difference between intraocular and intracranial pressure (ICP), rather than on intraocular pressure (IOP) itself. It has also been suggested that high blood pressure might correlate with the incidence of glaucoma; however, the data are contradictory. Here, we studied the effect of arterial blood pressure and changes in body position on TPG in rats.Methods: Experiments were performed on anesthetized 15- to 16-week-old, male, spontaneously hypertensive rats (hypertensive rats, n = 10) and Wistar–Kyoto rats (normotensive rats, n = 10). Continuous recordings of intracranial and IOPs were performed before, during, and after changing the body position from horizontal to vertical.Results: At baseline, hypertensive rats had a significantly higher arterial blood pressure than normotensive rats, while intraocular and intracerebroventricular pressures and TPG did not differ between the groups. Changing the body position from horizontal to vertical produced a significant decrease in ICP, a nonsignificant decrease in IOP, and a significant increase in the TPG. There was no significant difference between normotensive and hypertensive rats in the pattern of changes in intraocular and intracerebroventricular pressures and TPG.Conclusions: Change in the body position from horizontal to vertical, but not hypertension, causes a significant increase in TPG in rats. If further studies confirm that TPG plays a role in the etiology of glaucoma, a vertical position and changes in the body position might be considered as debilitating factors.