Effects of topical dihydroergocristine on intraocular pressure, aqueous humor dynamics and pupil diameter in conscious rabbits. A comparative study with timolol and pilocarpine.

This work comparatively studies the effects of dihydroergocristine, timolol and pilocarpine on intraocular pressure and pupil diameter in conscious rabbits. Intraocular pressure was measured by applanation tonometry and the pupil diameter by a photographic technique. In anesthetized rabbits, changes in tonographic facility of aqueous humor outflow and rate of aqueous humor formation were evaluated. Dihydroergocristine reduced the intraocular pressure more than timolol and much more than pilocarpine. The ocular hypotensive effect of dihydroergocristine was accomplished by a great reduction in aqueous humor formation, which surpasses the decrease in aqueous humor outflow, while timolol mainly reduced aqueous humor formation and pilocarpine increased aqueous humor outflow. Pupil diameter remained unchanged on dihydroergocristine, whereas timolol induced a slight mydriasis and pilocarpine provoked a clear myosis. Effects of dihydroergocristine might result in blockade of alpha-adrenoceptors in ciliary body, although available data about pretreatment with either metoclopramide or domperidone suggest that dopamine DA2-receptors might participate in ocular hypotensive effect of ergot derivatives.