Selective expression of endothelin 1 mRNA in rat retina

Endothelin is a potent vasoactive agent and three isoforms--endothelin 1 (ET-1), endothelin 2 (ET-2) and endothelin 3 (ET-3)-- have been found in ocular tissues. However its source has not been determined. Therefore we have investigated the ET mRNA in the rat retina using reverse transcriptase with polymerase chain reaction. For ET-1, three retina samples were positive. For ET-2 and ET-3, all samples were negative. ET-1 mRNA was abundantly expressed compared with ET-2 and ET-3 mRNA (p < 0.05). Our study provides direct evidence that ET-1 is abundantly synthesized in the rat retina. The ET-1 within the retina could contribute to the regulation of the retinal circulation through vessel contraction.