Pharmacological effects of pilocarpine on rabbit ciliary artery

A disturbance in ocular blood flow is an important factor in the pathogenesis of visual damage caused by glaucoma. We investigated the innervation of the ciliary artery, important to blood flow in the optic nerve head, and the effects of pilocarpine thereon.

Ciliary arteries were prepared from rabbit eyes and mounted in a myograph system. The effects of electrical nerve stimulation and pilocarpine on the isolated rabbit ciliary artery were investigated using isometric tension recording methods.

Electrical field stimulation evoked contraction of the ciliary artery, which was inhibited by pretreatment with 10 microM bunazosin. Electrical field stimulation also evoked relaxation when the ciliary artery was pre-contracted by 10 microM histamine in the presence or absence of endothelium. This relaxation was inhibited by pretreatment with 10 microM N(G)-nitro-L-arginine methylester (L-NAME). Pilocarpine administration produced a dose-dependent muscle relaxation that was abolished by treatment with L-NAME, 1 aeM atropine, or denudation of the endothelium.

Results indicate that the rabbit ciliary artery is innervated by at least two different types of nerves, adrenergic nerves, which evoke contraction and nerve fibers that cause an endothelium-independent release of nitric oxide (NO). Pilocarpine relaxation of this muscle was dependent on the endothelium and NO synthesis.