LIGHT SYNCHRONIZATION OF THE PREOVULATORY LH-SURGE IN ADRENALECTOMIZED RATS

Possible effects of adrenalectomy (adx) on light-dependent changes in the timing of the preovulatory LH [luteinizing hormone] surge were investigated. In the 1st experiment, female rats were maintained on a standard light schedule of 14 h light:10 h dark (lights on 0500-1900 h). Intact and adx rats showing at least 2 consecutive 4 day estrous cycles were bled at 1400, 1600, 1800 or 2000 h on proestrus. The timing and amplitude of the preovulatory surge of LH were very similar in intact and adx animals. In a 2nd experiment, intact animals were maintained under standard lighting conditions (lights on 0500-1900 h) 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 h light period was advanced 7 h (i.e., lights on 2200-1200 h). After 3 wk or more in the altered light environment, animals showing regular 4 day estrous cycles were bled at 0700, 0900, 1100, 1300 or 1500 h on proestrus. Both intact and adx rats showed an approximately 7 h shift 3u 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 primary synchronizing effects of light on the timing of the preovulatory LH surge in the rat apparently operate via mechanisms independent of the pituitary-adrenal system.