Retinal damage in hatched chicks induced by formoguanamine. Decrease in ornithine aminotransferase activity and...

Subcutaneous injection of formoguanamine (2,4-diamino-s-triazine) induced sightlessness in newly hatched chicks within 28-32 hr. The specific activity of retinal ornithine aminotransferase, localized exclusively in the mitochondria of retinal pigment epithelium, and the retinal vitamin B6 content decreased rapidly after formoguanamine administration. An absorption spectrum of retinal extract showed reduced absorbance at 400 nm in the formoguanamine-treated chicks, but delta 1-pyrroline-5-carboxylate reductase, an enzyme in the retinal cytosol, did not change significantly. A drug-metabolizing enzyme, glutathione transferase, showed an increase in specific activity during a later phase. Histological examination of the formoguanamine-treated chicks revealed characteristic degeneration of pigment epithelium and photoreceptors, acute retinal detachment and a secondary gliosis in the outer nuclear layer. From these findings it may be concluded that formoguanamine primarily damages the physiological functions of retinal pigment epithelium and photoreceptors and results in irreversible retinal detachment in newly hatched chicks.