The influence of acute and chronic cervical sympathectomy on the ocular hypotensive effect of clonidine.

The influence of clonidine on intraocular pressure was studied in chloralose-anesthetized cats. The cats were subjected to unilateral cervical sympathectomy, either acute or chronic. The drug was injected either intravenously or into the left vertebral artery. With the aim of investigating the role of the sympathetic nervous system in the central IOP-lowering effect of clonidine, the fall in IOP induced by the drug in these preparations was compared to the decrease in ocular pressure caused by clonidine in intact cats. An enhanced depressor effect in both eyes of unilaterally sympathectomized cats became evident after the intravenous injection of clonidine. In contrast, the effect of central administration was similar or even smaller than in intact cats. We conclude that the central IOP-lowering effect of clonidine is diminished after cervical sympathectomy, indicating that the peripheral sympathetic nervous system is the efferent pathway of this centrally initiated effect.