EFFECTS OF SOME OPIATES AND OPIOID PEPTIDE EYEDROPS ON OCULAR MELATONIN REGULATION IN RABBITS

Levels of melatonin in rabbit eye tissues were detected by radioimmuno assay. Solutions of met-enkephalin, leu-enkephalin, alin, alpha-endorp hin and beta-endorphin were given topically. Met-Enkephalin and alpha- endorphin lowered levels of melatonin in the iris, iris root-ciliary b ody, retina and choroid; leu-enkephalin raised levels in the retina an d lowered them in other tissues. beta-Endorphin only lowered levels in the iris root-ciliary body. DAGO (a mu agonist) given i.v. lowered le vels of melatonin in the iris, iris root-ciliary body and retina. The delta and sigma agonists given i.v. only lowered levels in the iris ro ot-ciliary body, and a kappa agonist given i.v. raised levels in the c iliary body. No opiate binding sites could be detected in the rabbit i ris or iris root-ciliay body for any class of receptor. Our data sugge st opioids may be useful for treating glaucoma.