Vitamin A metabolism in the baboon eye

The vitamin A metabolism of eight baboon (Papio cynocephalus anubis) eyes were examined. High performance liquid chromatography was utilized for quantitative analysis of retinyl esters and retinol in four eyes. Retinyl ester levels in pigment epithelium (PE) were greater (3043 pmol/eye) than in neuroretina (1084 pmol/eye). However, the reverse was true for retinol levels (neuroretina = 4610 pmol/eye; PE = 1451 pmol/eye). Neuroretina and PE of four remaining eyes were analyzed for retinyl ester hydrolase (REH) activity. Specific activity of 11-cis REH in neuroretina was 2.14 Units/mg while that of PE was 1.11 Units/mg (1 Unit of activity = 1 pmol of product formed/minute). In contrast, all-trans REH activity was greater in PE (1.78 Units/mg) than in neuroretina (0.41 Units/mg). Because the visual cells, vitamin A distribution and metabolism in the baboon eye are similar to those found in human ocular tissues, the baboon eye serves as an important primate model of the human visual system.