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Effects of topical alpha-substituted anandamides on intraocular pressure in normotensive rabbits
D W Pate1, K Järvinen, A Urtti
1Department of Pharmaceutical Chemistry, University of Kuopio, Finland. iha@euronet.nl
Purpose:
Anandamides have been observed to lower intraocular pressure in the rabbit eye, preceded by a period of hypertension. Amidases are thought to catabolize these compounds into their component parts, including arachidonic acid. Direct application of arachidonic acid has been observed to cause a marked rise of intraocular pressure. Thus, anandamide analogs resistant to catabolism were thought possibly devoid of this initial hypertension, and their effects on rabbit IOP investigated.
Methods:
A series of chiral alpha-substituted anandamides were synthesized and studied for their effect on the intraocular pressure (IOP) of normotensive pigmented rabbits. Each test compound was dissolved in an aqueous 2-hydroxypropyl-beta-cyclodextrin solution (containing 3% polyvinyl alcohol) and administered (62.5 micrograms) unilaterally to the eye.
Results:
The most promising compounds caused a statistically significant reduction of IOP (vs. vehicle) in the treated eyes. Of these, the R-alpha-isopropyl compound exhibited the best activity tested. Unlike the alpha-unsubstituted analogs previously studied, hypotensive effects were not preceded by an initial elevation of IOP and indomethacin pre-treatment (12.5 mg, s.c.) did not eliminate the IOP response, as demonstrated by administered R-alpha-isopropyl anandamide.
Conclusions:
Catabolism of alpha-unsubstituted anandamides may account for their observed intraocular hypertensive effects. The physiological mechanism by which alpha-substituted anandamides work apparently differs from that of the more easily metabolized alpha-unsubstituted compounds.