Intraocular pressure and systemic blood pressure after administration of vasoactive substances in hypertensive and normal rats

Intraocular pressure (IOP) and arterial blood pressure (BP) were recorded manometrically in normotensive Wistar Kyoto rats (NR) and stroke-prone spontaneously hypertensive rats (SHR). IOP was significantly lower in SHR (7.8 +/- 0.2 mm Hg) compared to NR (15.9 +/- 0.4 mm Hg). In NR, administration of vasoactive substances (kallikrein, bradykinin, angiotensin I and II) or bloodletting resulted in significant IOP reactions, which ran nearly parallel to the acute BP changes. In SHR, however, IOP showed little reaction after comparable changes in BP. The cause of the low IOP in SHR is unknown. It is assumed that in SHR rarefaction of arterioles and capillaries and a decrease in the compliance of eye vessels, in combination with an increase in the distensibility of the bulbus at this low IOP level, contribute to the lack of IOP response after administration of vasoactive drugs.