HORMONAL AND DIM LIGHT EFFECTS IN RETINAL PHOTODAMAGE*

Abstract

Abstract—Exposure of albino rats to continuous visible dim light results in the rapid. but graded. loss of photoreceptor cells. The age at which albino rats are exposed to light influences the degree of photoreceptor damage. The severity of cell destruction per unit exposure time gradually increases in rats exposed at different ages from postweaning to adulthood, and by 8 weeks of age, reduction in the thickness of the outer nuclear layer (photoreceptor cell nuclei) is highly significant. The period of increasing susceptibility to light damage is coincident with the occurrence of sexual maturation, which suggests a relationship between photoreceptor destruction and the maturation of the pituitary gland‐gonadal axis. To determine whether the absence of the pituitary gland and ovarian hormones influences photoreceptor damage, animals were either hypophysectomized or ovariectomized and exposed to continuous illumination for up to 45 days. The degree of photoreceptor destruction is significantly reduced in operated, as compared with sham‐operated control, rats exposed to an identical light regimen. Small, physiologic doses of estradiol reverse the protective effects of ovariectomy, but larger, pharmacologic doses do not. Retinal damage is significantly enhanced by injection of pituitary homogenates during the light‐exposure period and by transplantation of pituitary glands under the kidney capsule of rats in which the pituitary has been removed. Pituitary glands transplanted in this location produce high levels of prolactin, while other pituitary hormones are found at unusually low, and sometimes nonfunctional, levels. Prolactin administration to rats during the light exposure period effectively reverses the protection afforded by removal of the pituitary gland.Pituitary gland hormones as well as hormones from some of the pituitary target organs, appear to have a regulatory influence on the severity of light‐induced photoreceptor damage in this species.