Dopamine, PIF, and other regulators of prolactin secretion.

Considerable evidence now exists that dopamine is a physiological prolactin inhibiting factor (PIF); however, it may not represent the only PIF. Amphetamine, which releases newly synthesized dopamine and blocks prolactin release, caused an increased in dopamine levels in the pituitaryb gloand. Prolactin release appears to be regulated also by a prolactin releasing factor (PRF). A wide variety of hypothalamic peptides stimulate prolactin release, but only two of these (thyrotropin releasing hormone and vasoactive intestinal polypeptide) can act directly on the pituitary and thus are candidates for PRF.