Effect and Mechanism of Betaxolol and Timolol on Vascular Relaxation in Isolated Rabbit Ciliary Artery

Abstract

Betaxolol, a selective beta1-adrenoceptor antagonist, and timolol, a nonselective beta-adrenoceptor antagonist, both frequently used in the medical management of glaucoma, decrease [Ca2+]i by acting as Ca2+ channel blockers, thus causing relaxation of isolated rabbit ciliary artery.

Experimental Model of Ocular Hypertension in the Rat: Study of the Optic Nerve Capillaries and Action of Hypotensive Drugs

“…Timolol, a nonselective ␤-adrenoreceptor antagonist, lowers IOP by decreasing the formation of aqueous humor in the ciliary epithelium. 38 It has a hypotensive effect in the rat, 19 decreasing [Ca 2ϩ ] by acting as a Ca 2ϩ channel blocker, 39 and a neuroprotective effect on the RGCs and other neurons of the retina. 19,20,40,41 Applied topically, timolol reaches the retina-choroid at concentrations within the effective pharmacologic range.…”

Effects of Rho-associated protein kinase inhibitors Y-27632 and Y-39983 on isolated rabbit ciliary arteries

“…However, the underlying pharmacological mechanism is unclear. We therefore investigated the underlying mechanism of these drugs on vascular smooth muscles [6][7][8][9][10][11][12]. We examined whether these drugs relaxed the ciliary arteries by different mechanisms, such as nitric oxide (NO) release and inhibition of voltage-dependent or -independent calcium entry.…”

Medications Used to Treat Glaucoma

“…There is some evidence that betaxolol may increase retinal and choroidal blood flow by acting on voltage-dependent calcium channels. 102,[106][107][108][109][110][111][112][113][114][115] It may thus have some neuroprotective effect separate from its IOP lowering properties. 116,117 Levobunolol has an active metabolite (dihydrobunolol) that may contribute to its longer duration of activity when compared with timolol.…”