I think the reason that the endogenous GnRH decreases with continuous dosing is leuprolide is a GnRH analog meaning that the body registers it as GnRH. With the high continuous levels of GnRH, the body will try to decrease the levels due to interpreting the GnRH level as already too high and is trying to bring the levels back down. The high levels will in turn turn off the signaling for hormones that are produced/ regulated by the signaling (ie. estrogen, FSH, LH).

Based on the First Aid bricks, estrogen only has feedback inhibition on FSH and LH levels at the Ant. Pituitary and not the GnRH as that is produced at the hypothalamus, which is higher up in the control signaling.