title: Melatonin receptor agonist-induced reduction of SNP-released nitric oxide and cGMP production in isolated human non-pigmented ciliary epithelial cells.
abstract: The present study was designed to determine the effects of melatonin and its receptor agonists on SNP-released nitric oxide (NO) and cGMP production in aqueous humor producing cells of the ciliary body because these effects may play a role in melatonin receptor-mediated regulation of intraocular pressure (IOP). NO release protocols were carried out using human non-pigmented ciliary epithelial (hNPCE) cells treated in dye free DMEM containing l-arginine (10(-3) M). The cGMP experimental protocols were performed using dye free DMEM containing 3-isobutyl-1-methylxanthine (IBMX, 10(-4) M). The effects of varying concentrations (10(-13), 10(-11), 10(-9), 10(-7), and 10(-5) M) of melatonin, 5-MCA-NAT (putative MT(3) agonist), N-butanoyl-2-(2-methoxy-6H-isoindolo[2, 1-a]indol-11-yl)ethanamine (IIK7; selective MT(2) agonist) or S-27633-1 (selective MT(1) agonist) on sodium nitroprusside (SNP)-released NO or cGMP production were determined in separate experiments. NO and cGMP levels were measured using a colorimetric assay or enzyme immunoassay (EIA), respectively. Melatonin receptor selectivity was evaluated using luzindole (LUZ; nonselective MT(1)/MT(2) antagonist) or 4-phenyl-2-propionamidotetralin (4P-PDOT; selective MT(2) antagonist). Melatonin, 5-MCA-NAT, and IIK7 all caused concentration-dependent reduction of SNP-released NO and cGMP production. The inhibitory actions of melatonin, 5-MCA-NAT and IIK7 were either completely blocked at 10(-13), 10(-11), and 10(-9) M concentrations of the agonists or partially at 10(-7) and 10(-5) M in the presence of luzindole or 4P-PDOT. Results from this study suggest that melatonin and its analogs, 5-MCA-NAT and IIK7 inhibit SNP-released NO and cGMP production via activation of MT(2) receptors in human NPCE cells. These actions may play a role in melatonin agonist-induced regulation of aqueous humor secretion and IOP.
authors.affiliation: Department of Pharmacology and Toxicology Morehouse School of Medicine, 720 Westview Drive, SW, Atlanta, GA 30310-1495, USA. jcarnes@msm.edu
authors.forename: Juanita
authors.initials: J
authors.lastname: Dortch-Carnes
authors.forename: Gianluca
authors.initials: G
authors.lastname: Tosini
mesh_terms: D001082:Aqueous Humor / Q000502:physiology; D002478:Cells, Cultured; D002924:Ciliary Body / Q000187:drug effects* / Q000378:metabolism; D003124:Colorimetry; D006152:Cyclic GMP / Q000096:biosynthesis*; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D007118:Immunoassay; D007429:Intraocular Pressure / Q000502:physiology; D054833:Isoindoles / Q000494:pharmacology; D008550:Melatonin / Q000494:pharmacology*; D009569:Nitric Oxide / Q000378:metabolism*; D009599:Nitroprusside / Q000633:toxicity*; D044122:Receptor, Melatonin, MT1 / Q000819:agonists; D044123:Receptor, Melatonin, MT2 / Q000819:agonists*; D044094:Receptors, Melatonin / Q000819:agonists; D014363:Tryptamines / Q000494:pharmacology
chemical_list: C413586:5-methoxycarbonylamino-N-acetyltryptamine; C121417:IIK7; D054833:Isoindoles; D044122:Receptor, Melatonin, MT1; D044123:Receptor, Melatonin, MT2; D044094:Receptors, Melatonin; D014363:Tryptamines; D009599:Nitroprusside; D009569:Nitric Oxide; D006152:Cyclic GMP; D008550:Melatonin