Effects of topical PGF_2α on aqueous humor dynamics in cynomolgus monkeys

Abstract

Single topical applications of prostaglandin F_2α (PGF_2α) tromethamine salt to living cynomolgus monkey eyes reduced intraocular pressure (IOP). Twice daily topical application was far more effective, so that after the 7th 50 μg or 100 μg dose on day 4, IOP fell 40–50%, to 8–10 mm Hg. Following twice daily application of 50 or 100μg for > 3 days: (1) no increase in total outflow facility could be demonstrated by 2-level constant pressure perfusion or Schiotz tonography; (2) no decrease in aqueous humor formation rate could be demonstrated by fluorophotometry-rather, aqueous flow may have increased; (3) anterior chamber aqueous humor protein concentration was unaltered, but entry of intravenously injected fluorescein into the cornea and anterior chamber tended to increase; (4) there was a weak but sometimes statistically significant miosis of up to ∼ 0.5 mm. We conclude that in the oynomolgus monkey: (1) PGF_2α is a potent ocular hypotensive agent with only very weak miotic and blood-aqueous barrier-disrupting effects; (2) the ocular hypotensive action of PGF_2α is definitely not due to increased conventional outflow facility or decreased aqueous production, but probably to increased uveoscleral drainage of aqueous humor.