Circadian rhythm in the retinal pigment epithelium related to vitamin B12

The wake-sleep rhythm is a typical circadian rhythm. It has been reported that severely disturbed wake-sleep rhythms are improved by the administration of vitamin B12. This study was designed to clarify whether vitamin B12 is universally related to the circadian rhythm. Three-week-old male Wistar Kyoto rats were fed a vitamin B12 deficient diet for 3 months. Then some of them were given intraperitoneal injections of vitamin B12. We counted phagocytized lamellar structures in the retinal pigment epithelium after the start of exposure to light in negative electron microscopic films. In vitamin B12 deficient rats, the maximum number of phagocytized lamellar structures in the retinal pigment epithelium appeared 3 hours after the start of light exposure, while in the control and vitamin B12 injected groups the peak occurred at 2 hours. This difference suggests that the retinal circadian rhythm is closely related to the level of vitamin B12.