Fig. 1.

Effect of central administration of KOR antagonist on pulsatile LH release in OVX rats treated with a negative feedback level of E₂ (low E₂). Profiles of LH release in representative OVX + E₂ rats treated with nor-BNI, a KOR antagonist, or vehicle (A). Nor-BNI or vehicle (UPW) was injected into the 3V immediately after the start of blood sampling (arrows). Blood samples were collected for 3 h at 6-min intervals. Arrowheads indicate the peaks of LH pulses identified by the PULSAR computer program. Mean plasma LH concentrations and frequency, amplitude and baseline levels of LH pulses in low E₂-treated OVX rats (B). Values are means ± SEM. The numbers in each column represent the numbers of animals used in each group. * P < 0.05 vs. the vehicle-treated controls (Student's t-test).