PULSATILE LUTEINIZING-HORMONE RELEASE ON DIESTRUS DAY-2 IN INTACT ANDIN DIESTRUS DAY-1 OVARIECTOMIZED CYCLIC RATS TREATED WITH THE ANTIPROGESTERONE-RU486

Administration of antiprogesterone RU486 (4 mg/0.2 ml oil) at 0900 h o n diestrus day 1 (metestrus) and diestrus day 2 to adult 4-day cyclic rats increased basal LH plasma concentration on diestrus day 2 afterno on and ovariectomy at metestrus (0900 h) reduced the RU486-induced inc rease in LH concentration to the values found in ovariectomized-oil tr eated rats. Despite the increase in mean LH levels in RU486-treated ra ts, LH pulse frequency, duration and relative amplitude remained uncha nged, indicating that other ovarian factor (s) different from progeste rone are involved in the effect of RU486 on the basal aspects (trough levels) of LH secretion during diestrous in the cyclic rat.