Light Synchronization of the Preovulatory LH Surge in Adrenalectomized Rats 1

Summary

Possible effects of adrenalectomy (adx) on light-dependent changes in the timing of the preovulatory LH surge have been investigated. In the first experiment, female rats were maintained on a standard light schedule of 14 hr light: 10 hr dark (lights on 0500-1900 hr). Intact and adx rats showing at least two consecutive 4-day estrous cycles were bled at 1400, 1600, 1800, or 2000 hr on proestrus. The timing and amplitude of the preovulatory surge of LH were very similar in intact and adx animals. In a second experiment, intact animals were maintained under standard lighting conditions (lights on 0500-1900 hr) until the establishment of regular 4-day cycles. Intact rats and experimental animals immediately after adx were then transferred to an altered light regime in which the 14-hr light period was advanced 7 hr (i.e., lights on 2200-1200 hr). After 3 weeks or more in the altered light environment, animals showing regular 4-day estrous cycles were bled at 0700, 0900, 1100, 1300, or 1500 hr on proestrus. Both intact and adx rats showed an approximately 7-hr shift in the timing of the preovulatory surge of LH. However, the adx animals required a longer period of time to reestablish regular cycles when placed in the altered light environment than did the intact rats. The results indicate that the primary synchronizing effects of light on the timing of the preovulatory LH surge in the rat operate via mechanisms independent of the pituitary-adrenal system.