Vitamin A metabolism in primary retinitis pigmentosa.

The serum vitamin A (VA) and retinol body pool response (RBPR) were studied in 28 cases of retinitis pigmentosa (RP), in comparison to 7 unaffected RP family members and 10 normal individuals. Serum VA was found to be normal in all 3 groups, with no significant difference between any 2 groups. The RBPR was also normal in all 3 groups, but the RBPR of the RP patients and their unaffected family members were significantly higher than the normal respectively (P less than 0.001), suggesting that the pigment epithelium or rod photoreceptor of the former groups were deficient in VA, whether from disturbed utilization or abnormalities in their retinol-binding protein, that abnormally high feedback stimuli were sent out calling for a VA supply to the target site with less retention in the liver.