Topical forskolin (colforsin) and aqueous flow in humans

A 1% forskolin (nonproprietary name, colforsin) suspension was instilled in one eye each of 15 normal human subjects in a single-dose experiment under the following three conditions: during the day, during the night while asleep, and following pretreatment with timolol maleate. The rate of flow was 2.6 +/- 0.13 microL/min (mean +/- SE) in the afternoon in both the treated and the untreated eyes. During sleep at night the flow was lower than in the afternoon in both the placebo-treated eye, 1.5 +/- 0.09 microL/min, and the forskolin-treated eye, 1.3 +/- 0.09 microL/min. Timolol pretreatment reduced the flow to 1.6 +/- 0.08 microL/min in the placebo-treated eye and 1.6 +/- 0.10 microL/min in the forskolin-treated eye. No statistically significant effects of forskolin on flow were observed under any of the conditions. Forskolin caused transient hyperemia in all subjects. The experiment confirmed previous reports of differences in the rate of aqueous flow at different times of day and the effect of the beta-adrenergic blocker timolol on the rate of aqueous humor flow.