Influence of environmental lighting on decidualization in the rat.

Abstract

Adult, virgin Holtzman rats, maintained in a 14-hr light⁄day photoperiod, were transferred during proestrus to an environment of 2 hr light⁄day or 22 hr light⁄day. Pseudopregnancy (Day 0 = estrus) was induced upon transfer (0 days pre-exposure, 0 estrous cycles) or following short (1 estrous cycle) or long (5 estrous cycles) pre-exposure to an experimental photoperiod. Decidual sensitivity, assessed after surgical traumatization of the uterus, was measured as uterine weight 5 days post trauma. Sensitivity to decidualization in control animals was absent on midnight of Day 2, but developed rapidly to a peak (2000 mg⁄cornu) during the interval between midnight of Day 3 and noon of Day 4 of pseudopregnancy. A rapid loss of sensitivity occurred afterward. In relation to controls, 0 and 1 cycle of pre-exposure to 2 hr light⁄day did not significantly alter the time of onset of decidual sensitivity, though a decreased magnitude of response and a slightly earlier regression were noted. Long pre-exposure to 2 hr l...