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Increase in ocular blood flow induced by isobutylmethylxanthine and epinephrine
M J Busch1, J Stjernschantz, P F Hoyng
1Department of Experimental Ophthalmology, Netherlands Ophthalmic Research Institute, Amsterdam.
Abstract:
Alterations in regional blood flow of the eye were studied in rabbits using the radioactively labelled microsphere technique. The animals were topically treated with 1% IBMX, 0.1% epinephrine in combination with 1% isobutylmethyl-xanthine (IBMX), or with 0.1% epinephrine alone. After IBMX there was a tendency towards an increase in blood flow in the iris, ciliary processes and sclera, whereas the choroidal blood flow tended to decrease. After epinephrine the iridial blood flow increased about 50% at 6 hr. After IBMX combined with epinephrine a biphasic response was obtained: an initial decrease in blood flow of the iris, the ciliary processes and to some extent the choroid was followed by a marked and long lasting increase in blood flow from 2.5 to 7.5 hr in the iris (up to 220%), ciliary processes (123%) and sclera (115%). The choroidal blood flow was not increased. The marked increase in blood flow of the iris and the ciliary processes indicates that the reduction of intraocular pressure seen after topical treatment with a combination of epinephrine and IBMX, is not based on a vascular mechanism. The increase of ocular blood flow after a combination of IBMX and epinephrine is probably based on increased cAMP secondary to inhibition of phosphodiesterases. This may indicate the presence of beta-adrenergic receptors in the ocular vasculature.
Insights
Topical isobutylmethyl-xanthine (IBMX) and epinephrine increased ocular blood flow, particularly in the iris and ciliary processes. This suggests the intraocular pressure reduction is not vascular-mediated and may involve beta-adrenergic receptors.
Area of Science:
- Ophthalmology
- Pharmacology
- Physiology
Background:
- Ocular blood flow regulation is crucial for eye health.
- Epinephrine and phosphodiesterase inhibitors like IBMX are used in ophthalmic treatments.
- Understanding their vascular effects is key to elucidating mechanisms of action.
Purpose of the Study:
- To investigate the effects of IBMX and epinephrine on regional ocular blood flow in rabbits.
- To determine if observed intraocular pressure changes are vascular-related.
- To explore potential mechanisms involving adrenergic receptors.
Main Methods:
- Radioactively labeled microsphere technique used in rabbits.
- Topical administration of 1% IBMX, 0.1% epinephrine, or combination.
- Measurement of blood flow in iris, ciliary processes, sclera, and choroid.
Main Results:
- IBMX alone showed a trend towards increased iris, ciliary process, and scleral blood flow, with decreased choroidal flow.
- Epinephrine increased iridial blood flow by ~50% at 6 hours.
- The combination induced a biphasic response: initial decrease followed by significant, sustained increases in iris (up to 220%), ciliary processes (123%), and sclera (115%), but not choroid.
Conclusions:
- The marked increase in ocular blood flow with the IBMX-epinephrine combination suggests the intraocular pressure reduction is not primarily vascular.
- Elevated cAMP secondary to phosphodiesterase inhibition likely mediates the increased blood flow.
- Findings suggest the presence of beta-adrenergic receptors in ocular vasculature.