OCULAR ACTION OF AN OPIOID PEPTIDE, DPDPE

This study was performed to examine some ocular actions of an opioid a gonist. Experiments were performed to evaluate the effects of a delta opioid agonist, DPDPE ([D-pen(2), D-pens]enkephalin (where pen = penic illamine)), on: 1) intraocular pressure (IOP) in rabbits; 2) cAMP accu mulation in rabbit iris ciliary bodies (ICBs). Unilateral, topical adm inistration of DPDPE caused bilateral depression of IOP. Intravitreal injection of DPDPE caused a greater IOP decrease than intravitreal inj ection of NaH2PO4 (vehicle). Topical administration of naloxone partia lly inhibited the effect of DPDPE on IOP in normal rabbits. In other e xperiments, DPDPE suppressed both basal and isoproterenol (ISO)-stimul ated cAMP accumulation in ICBs. The presence of naltrindole (NTI), a d elta receptor antagonist, did not prevent the suppression of cAMP leve ls by DPDPE. The conclusions drawn from the findings suggest that the lowering of IOP by DPDPE is mediated, in part, by actions at postjunct ional (ciliary body) sites and may involve an atypical opioid receptor .