Prolactin and Antipsychotic Medication

Abstract

Prolactin is a hormone secreted by the lactotroph cells of the anterior pituitary gland. Although it is present in both males and females of all ages, its main function in humans is to stimulate the production of breast milk in the postpartum period. Like other pituitary hormones, prolactin is regulated by the hypothalamus, which produces factors which stimulate and inhibit its synthesis and secretion. In the case of prolactin, the primary hypothalamic regulation is a tonic inhibition of its secretion which is mediated by dopamine, a neurotransmitter produced in the hypothalamus and secreted into the hypothalamic–pituitary portal capillaries which then carry it to the anterior pituitary gland. Dopamine acts on D2–dopamine receptors on the pituitary lactotroph cells to inhibit both synthesis and secretion of prolactin. Although the hypothalamus also produces prolactin–stimulating factors such as thyrotropin–releasing hormone (TRH) and vasoactive intestinal polypeptide (VIP), these appear to play minor roles in regulating prolactin secretion in humans. All conventional (first generation) antipsychotic agents act as antagonists on the D2–dopamine receptor. Atypical (second generation) antipsychotics are more variable in their affinity for the D2 receptor and thus vary in their effects on prolactin secretion. The relative potency of antipsychotic agents in elevating serum prolactin is: