Increase in ocular blood flow induced by isobutylmethylxanthine and epinephrine.

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.