ALPHA-MELANOCYTE STIMULATING HORMONE (ALPHA-MSH) ENHANCES EICOSANOID PRODUCTION BY BOVINE RETINAL-PIGMENT EPITHELIUM

Explants of bovine eyes consisting of retina, with its underlying choroid and sclera (termed retinal explants) were maintained in organ culture in the absence or presence of alpha-melanocyte stimulating hormone (alpha-MSH) for up to 19 days. The conditioned media was collected twice a week and assayed for the following eicosanoids, prostaglandin E2 (PGE2) and prostacyclin. The addition of alpha-MSH to the incubation media resulted in a 1.5 fold enhancement in the production of both PGE2 and prostacyclin. This stimulatory effect diminished after 11 days. Additionally, the three tissue components comprising the retinal explants i.e. 1. neural retina 2. retinal pigment epithelium (RPE) with its underlying vascular layer (choroid) and 3. scleral tissue were separated and incubated in the presence or absence of alpha-MSH. Hormone treatment caused an enhanced eicosanoid production by RPE tissue alone, while its production by the neuronal retina and sclera was reduced or unaffected respectively. This demonstrates that the RPE layer is the source for the alpha-MSH induced eicosanoid production observed in the whole retinal explant. Our findings demonstrate, for the first time that alpha-MSH can stimulate prostaglandin production by RPE maintained in organ culture.