Alpha melanocyte stimulating hormone (α-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 α-melanocyte stimulating hormone (α-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 α-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 α-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 α-MSH induced eicosanoid production observed in the whole retinal explant. Our findings demonstrate, for the first time that α-MSH can stimulate prostaglandin production by RPE maintained in organ culture.