Inhibition by brimonidine of forskolin-induced nitric oxide synthase expression in human ciliary bodies in vitro

PURPOSE: To investigate the mRNA and protein expression of nitric oxide synthase (NOS) in human ciliary bodies in vitro. The effect of the adenylcyclase activator forskolin and/or the α(2)-adrenergic agonist brimonidine (an ocular hypotensive agent that inhibits aqueous humor formation) on NOS mRNA or protein expression was also studied. METHODS: Frozen human ciliary bodies obtained from local eye bank were thawed and incubated with 0.1 mM forskolin for 24 h in the absence or in the presence of 100 μM brimonidine. The mRNA and protein expression of three NOS isoforms (neuronal NOS or nNOS, inducible NOS or iNOS, endothelial NOS or eNOS) were assessed by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis, respectively. RESULTS: mRNA and protein expression of three NOS isoforms were detected in human ciliary bodies. Forskolin significantly up-regulated the mRNA and protein expression of nNOS, but not that of iNOS or of eNOS. In the presence of brimonidine, the forskolin-induced up-regulation of nNOS mRNA or protein expression was significantly inhibited. CONCLUSIONS: In human ciliary body (where aqueous humor is produced), brimonidine inhibits the up-regulation of nNOS expression induced by forskolin.