Tohoku J. Exp. Med., 2001, 195 (4)

Effects of a b-Adrenergic Blocking Agent Timolol on Intra Ocular Pressure Responses Induced by Stimulation of Cervical Sympathetic Nerve in the Cat

AKIRA NAITO, HIROSHI IZUMI,¹ KEISHIRO KARITA¹ and MAKOTO TAMAI

Department of Ophthalmology, Tohoku University Graduate School of Medicine, and ¹Deptartment of Oral Molecular Bioregulation, Tohoku University Graduate School of Dentistry, Sendai 980-8575

We clarified whether the intraocular pressure (IOP) response elicited by stimulation of the cervical sympathetic nerve (CSN) is influenced by changes in the baseline of IOP level and by b-adrenergic blockade. The CSN was stimulated electrically for 30 seconds (10 V, 0.1-100 Hz, 2 milliseconds pulse duration) in urethane (100 mg/kg i.v.)-chloralose (50 mg/kg i.v.)-anesthetized, paralyzed cats. The IOP was monitored manometrically, and a controlled saline infusion was delivered into the anterior chamber to gradually increase IOP. CSN stimulation was delivered at the various baseline IOP levels so obtained. When required, a b-adrenergic blocker timolol (2%) was delivered into the conjunctival cul-de-sac. The normal IOP in our cats was 25±3 mmHg. This value decreased transiently on CSN stimulation. The amplitude of this IOP response depended on stimulus frequency and the pre-stimulus baseline IOP level. Topical administration of timolol increased the IOP response to CSN stimulation at a given baseline level. These results suggest that b-adrenergic blockade increases the a-adrenergic mediated-IOP reduction elicited by CSN stimulation at given baseline IOP level.

Keywords —— Intra ocular pressure; b-blocker; timolol; cervical sympathetic nerve; cat

© 2001 Tohoku University Medical Press

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Tohoku J. Exp. Med., 2001, 195, 219-225

Address for reprints: Dr. Keishiro Karita, Department of Oral Molecular Bioregulation, Tohoku University Graduate School of Dentistry, Sendai 980-8575, Japan.

e-mail: karita@physiol.dent.tohoku.ac.jp