The Influence of Progesterone and Estradiol on the Acute Changes in Pulsatile Luteinizing Hormone Release Induced by Ovariectomy on Diestrus Day 1 in the Rat

The aim of this study was to determine whether the rapid increases in LH pulse amplitude and frequency that occur within 24 h after ovariectomy (ovx) on diestrus day 1 (Dl) were due to the removal of progesterone (P) and/or estradiol (E). Initial studies demonstrated that plasma levels of E and P were 18.2 ± 1.2 pg/ml and 34.1 ± 3.2 ng/ml, respectively, between the evening of Dl and the morning of D2 in our colony of intact rats. Immediately after ovx and jugular venous cannulation on the morning of Dl, rats were implanted either with empty Silastic capsules or capsules capable of restoring physiological levels of E and P to the control values reported above. These rats were continuously bled (75 μl/6 min) for 3 h 1 day after ovx for analysis of pulsatile LH release, and then additional plasma samples were gathered for determination of E and P levels. Rats with empty capsules had decreased levels of E and P and increases in mean blood LH levels, LH pulse amplitude, and pulse frequency. Animals with E caps...