The central ocular hypotensive effect of clonidine

Abstract

Clonidine was administered into the left vertebral artery of anesthetized cats. A dose-response curve of the lowering effect on intraocular pressure (IOP) has been made and compared with the dose-response cure obtained after intravenous administration. A more pronounced decrease in IOP after the first route of administration became evident. The effect is not secondary to a stronger reduction of blood pressure by centrally injected clonidine. Distribution experiments with 14C-clonidine revealed no direct connection between the vertebral arteries and the blood supply of the eye. For 2 h the concentrations in the eye are somewhat lower than after intravenous administration. Therefore, the IOP-lowering effect is not due to a direct influence of clonidine on the eye. It is submitted that the clonidine-induced reduction in IOP is at least in part due to a central mechanism, in which the stimulation of central alpha-adrenoceptors and adrenergic neurons may be involved. The relevance of this hypothesis with regard to a possible central regulation of IOP is discussed.

Short-term Effects of Unilateral 1% Apraclonidine Therapy

“…This fellow eye effect may be due to a central neural action similar to that observed with topical clonidine. [6][7][8][9] This contralateral effect may make it more difficult to determine the effica¬ cy of IOP lowering by apraclonidine if a one-eye therapeutic trial is used in eyes with glaucoma.14 Topical 1% apraclonidine hydro¬ chloride caused no significant change in the facility of aqueous outflow. These tonographic results are similar to those involving topical clonidine.8 Apraclonidine decreases aqueous hu¬ mor flow approximately 30% in fluorophotometric studies according to R. F. Brubaker, MD (written commu¬ nication, Aug 31, 1987).…”

The influence of δ9-Tetrahydrocannabinol on intraocular pressure in the anaesthetized cat

“…The antihypertensive drug clonidine decreases IOP, at least in part, by a central mechanism, probably via the stimulation of a-adrenoceptors in the pontomedullary area (Innemee and van Zwieten, 1979). This conclusion is derived from the observation that administration of the drug via the vertebral artery to the brain stem of cats induced a more pronounced decrease in IOP than its intravenous injection.…”

Sustained Decreases in Systemic Blood Pressure Do Not Cause Ocular Hypotension

“…Concomitant de creases in both intraocular pressure and sys temic blood pressure have been reported with a variety of ocular hypotensives, nota bly clonidine [5,15,16], In other studies, however, the systemic and ocular depressor responses to clonidine [17] and timolol [8] were not temporally related. This profile of activities suggests that a complex relation- ship between blood pressure and intraocular pressure might exist.…”