Purpose: To compare the efficacy of topical tetrandrine (an alkaloid isolated from the Chinese medicinal herb Radix Stephania tetrandrae S) and timolol 0.5% ophthalmic solution on lowering the intraocular pressure (IOP) in ocular normotensive and hypertensive rats.
Methods: The experiment was designed as 2 parts. In the first part, normal male Sprague-Dawley rats were divided into 4 groups followed by topical administration once of 0.1%, 0.2%, 0.3% tetrandrine, and 0.5% timolol in the right eye, 0.9% saline was administered once at the opposite eye as control. In the second part, the ocular hypertension model was induced unilaterally in the rats by a diode laser treatment. Twice daily applications of the above drugs were delivered to hypertensive eyes. The control group was administered 0.9% saline. The TonoPen XL tonometer was used to determine the IOP levels.
Results: No lowering effect on IOP was detected in the normotensive rats treated with tetrandrine whereas timolol significantly reduced IOP in normotensive eyes. Both tetrandrine and timolol significantly reduced the IOP levels in the hypertensive eyes compared with the levels in the saline-treated groups. All concentrations of tetrandrine used in this study showed significant reduction of IOP in the laser-induced hypertensive eyes. Tetrandrine 0.3% had a similar efficacy as 0.5% timolol in reducing elevated IOP in ocular hypertensive eyes.
Conclusions: This study provides evidence that tetrandrine has a major effect on lowering IOP levels in the ocular hypertension rat model. The functional mechanisms of tetrandrine require further investigation.