Ocular pigmentation and intraocular pressure response to forskolin.

We studied the effects of a forskolin suspension on intraocular pressure (IOP) in normal albino and pigmented rabbits and in alpha-chymotrypsin induced ocular hypertensive rabbits. Experimental-induced ocular hypertensive rabbits were produced by injecting of alpha-chymotrypsin (167 units) into the posterior chamber of the eye of albino rabbits. Ocular hypertensive rabbits were classified into 3 groups according to the IOP (Group A; 15-19 mmHg, B; 20-24 mmHg, C; 25-29 mmHg). Topical application of 1% forskolin caused a significant decrease in IOP in Groups B and C, as well as in normal albino and pigmented rabbits. The hypotensive effects were lower in pigmented rabbits than in albino rabbits, although the duration was longer. Subconjunctival injection of 1% forskolin reduced IOP 1 to 5 hrs after treatment in albino rabbits. However, in pigmented rabbits, a slight increase in IOP was observed at 30 min, followed by a significant decrease 5 to 10 hrs after injection. Furthermore, the binding ability of forskolin to melanin granules was determined in vitro. Forskolin exhibited specific affinity towards melanin granules obtained from bovine eyes, with the binding reaching a plateau after 5 min of incubation.