Acute effects of topical forskolin on aqueous humor dynamics in man

Previous reports concerning the acute effects of topical forskolin on the intraocular pressure (IOP) and the aqueous humor dynamics in human eyes gave conflicting results, and this led us to reevaluate the effects of this drug in a total of 20 young normal Japanese volunteers. Fifty microliter of 1% forskolin was instilled in one eye, and the vehicle to the fellow control eye. After two instillations of the drug at an interval of 5 minutes, the maximum IOP fall of 2.4 +/- 1.3 mmHg occurred after 1 hour; a single instillation had no significant effect. The effects on the aqueous flow rate and iris permeability factor were determined by the oral fluorescein method. Two instillations of the drug reduced the aqueous flow rate to 87 +/- 7% of the control, while the iris permeability factor was increased to 114 +/- 11% (mean +/- SD, N = 10, P less than 0.005). Pretreatment with topical 0.25% 1-timolol in both eyes 1 hour prior to the drug administration did not significantly alter the forskolin effects.