Role of the hypophyseal neurointermediate lobe in the dynamic release of prolactin

The dynamic release of prolactin (PRL) occurs in a region of the anterior pituitary lobe (AP) that receives its blood supply primarily from the hypophyseal neurointermediate lobe (NIL) via the short portal vessels. This relationship, coupled with a growing body of supportive evidence, suggests that the hypophysiotropic signal mediating the massive discharge o f 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 a-MSH.