Intraocular pressure following systemic administration of cannabinoids

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Abstract
Various cannabinoids have been tested for activity compared to Δ9-THC in reducing intraocular pressure after intravenous administration in rabbits at 0.1 mg or 1 mg/animal. Comparison of ℓ-Δ9-, Δ8-, 11-0H-Δ9- and 11-0H- Δ8-THC indicates that minor configurational changes have only a small influence on activity with regard to induction of a fall in intraocular pressure, although 11-OH-Δ8-THC has increased activity. 8α-OH-, 8α-diOH- and 8β-diOH-Δ9-THC have little or no activity but 8β-OH-Δ9-THC is as active as Δ9-THC indicating that the hydroxyl group in the β-position does not influence activity. Modification of the C5H11 alkyl side chain (3'-0H-Δ9-THC) reduced activity to 20% relative to Δ9-THC. Cannabidiol (CBD), cannabichromene, cannabigerol and olivetol had no activity, but 10-OH-CBD had some activity at 2 mg/animal. Cannabinol (CBN) had about half the activity of Δ9-THC and activity was reduced further with l'-OH-CBN, indicating that side chain modification reduced activity. Neither Δ9-THC, nor cannabigerol, had any effect on intraocular pressure or total outflow facility in the rhesus monkey, suggesting species differences in ocular responses to cannabinoids. Further studies on modification of these compounds is warranted in order to further delineate the structure-activity relationships.