Comparison of effects of topical ibopamine and epinephrine on the circadian rhythm of intraocular pressure of the rabbit eye as measured by telemetry.

The purpose of this study was to measure the effect of topical ibopamine and epinephrine on intraocular pressure in undisturbed rabbits. Six pigmented rabbits were outfitted with a telemetric transducer system connected via catheter to the vitreous cavity of one eye for continuous monitoring of intraocular pressure. After entrainment to a 12 hour light, 12 hour dark cycle and after stabilization of the circadian rhythm of intraocular pressure, the animals were tested with 2% ibopamine and 2% epinephrine. Each drug was instilled during the light phase and during the dark phase of the circadian cycle. When administered during the light phase, both drugs caused a transient pressure rise followed by prolonged hypotension. When administered during the dark phase, neither drug caused a pressure rise but both drugs caused prolonged hypotension. It was concluded that ibopamine and epinephrine cause identical intraocular pressure changes in the normal rabbit eye. The effect was dependent on the timing of administration during the circadian cycle. Since ibopamine is a pro-drug of deoxyepinephrine (N-methyl dopamine, epinine), its effects are assumed to be due to this metabolite, a metabolite that is structurally similar to epinephrine.