Negative feedback Mechanism.

If the body needs a particular hormone, for instance lets say Gonadotropins, the GnRH will come from the hypothalamus via the portal vein to the anterior pituitary and Gonadotropin (LH and FSH) will be released.

Now if the body doesnt need the hormone anymore, a signal will be sent to the hypothalamus to release the GnIH or Gonadotropin Inhibiting Hormone which will be sent to anterior pituitary and GnRH release will be inhibited.

This is called negative Feedback Mechanism. This happens because our endocrine glands tend to over-secrete its hormones.

 

Hope this answers the question.