ROLE OF THE HYPOPHYSEAL NEUROINTERMEDIATE LOBE IN THE DYNAMIC RELEASEOF PROLACTIN

The dynamic release of prolactin (PRL) occurs in a region of the anter ior pituitary lobe (AP) that receives its blood supply primarily from the hypophyseal neurointemzediate lobe (NIL) via the short portal vess els. This relationship, coupled with a growing body of supportive evid ence, suggests that the hypophysiotropic signal mediating the massive discharge of AP PRL derives from the NIL rather than the hypothalamic median eminence, as previously believed. Moreover a major component of this signal appears to be alpha-MSH.