Substitution of porphyropsin for rhodopsin in mouse retina

Weanling, male albino mice were placed on a vitamin A-free diet for three months to deplete their vitamin A stores. The vitamin A-deficient mice were injected intraperitoneally with all-trans 3-dehydroretinol. 3-dehydroretinol was rapidly incorporated into the liver as a fatty acid ester. The chromophore of visual pigment increased gradually and reached a normal level 13 days after the injection. 3-Dehydroretinal accounted for 95% of the total chromophore in the retina. The high proportion of 3-dehydroretinal was observed also in the long-term experiment which was continued for six weeks with the injection of 3-dehydroretinol once a week. When the animal was injected with a mixture of 3-dehydroretinol and retinol, the ratio of dehydroretinal/retinal in the retina was far lower than the ratio of dehydroretinol/retinol in the liver. These results indicate that 3-dehydroretinol is not converted to retinol in mouse and is used less efficiently than retinol for the chromophore of visual pigment. The synthesis of visual pigment was observed even when the animal was kept in complete darkness after the injection of all-trans 3-dehydroretinol. This fact indicates that light is not required for the production of 11-cis chromophore of visual pigment.