Purpose: The effects of several serotonergic agonists on aqueous humor formation (AHF), total outflow facility (OF) and intraocular pressure (IOP) were investigated in living cynomolgus monkeys.
Methods: We determined the effect of a single topical unilateral 300 microg or 3 mg dose of the 5-HT agonists serotonin, 5-carboxamidotryptamine (5-CT), sumatripan, gepirone, and 8-hydroxy-2(di-n-propylaminotetralin) (8-OH-DPAT) and a 450 microg dose of flesinoxan on IOP (Goldmann applanation tonometry), AHF (scanning ocular fluorophotometry) and total OF (8-OH-DPAT only, topically and intracamerally).
Results: Serotonin, 5-CT, sumatripan or gepirone had no significant effect on IOP or AHF. 8-OH-DPAT caused an AHF increase of approximately 70% over 6 hr in both ipsilateral drug- and contralateral vehicle-treated eyes, but no significant change in IOP compared with baseline measured on a separate occasion in the same animals. 8-OH-DPAT did not increase protein levels or rate of entry of systemically administered fluorescein in the anterior chamber aqueous humor compared to historic controls, and no difference was seen between ipsilateral and contralateral eyes. Flesinoxan had no effect on IOP and produced an insignificant 25% increase in flow in treated eyes compared to baseline.
Conclusion: The results for 8-OH-DPAT and possibly flexinoxan indicate the presence of a secretion-stimulating 5-HT1A receptor in monkey ciliary epithelium that has little effect on IOP. OF was unchanged following 8-OH-DPAT administered topically or following intracameral exchange.