Exposure to constant light increases pineal weight and RNA content in the pineal of the vizcacha (Lagostomus maximus maximus).

The following parameters, RNA and protein content, gland weight and nuclear size were studied in pineal glands of adult male vizcachas, maintained in captivity under permanent light (Lot I) and darkness (Lot II). The same determinations were performed in pineals of vizcachas shot at night in their normal habitat (Lot III, Control lot). A significant rise of gland weight and RNA content was observed in Lot I (with respect to the Control lot), while nuclear size and protein content were unchanged. The only significative differences between Lots I and II were also found in the pineal weight and RNA content. These results indicate that exposure of vizcachas to permanent light for 10 days does not produce inhibition of the parameters under study as occurs in other species. Apparently, the light acts as a stressor in these nocturnal mammals.