Comparative effects of continual lighting and pinealectomy on the eyes, the harderian glands and reproduction in pigmented and albino rats

1. 1. Exposure of albino Sprague-Dawley and pigmented Long Evans rats to continuous lighting for 65 days resulted in significant regression of the ovaries, the Harderian glands and the pineal glands. Similarly, both strains of rats in constant lighting exhibited an increased incidence or cornified cells in their vaginal smears. None of these responses were affected by pineal removal. 2. 2. Albino rats, but not pigmented rats, also exhibited gross hypotrophy of their eyes and retinas after continual light exposure. Histological examination of the retinas of rats kept in continual light for 65 days revealed that the photoreceptor layer of the albino rats had degenerated and disappeared while only minor changes were seen in the retinas of the pigmented animals. 3. 3. The pineal glands of pigmented rats were found to be only two-thirds the size of those in albino animals but had about the same relative hydroxyindole-O-methyltransferase activity.