ICD-10 Code
Е22.1 Hyperprolactinemia.
General Information
Prolactin was discovered in 1928 as a lactogenic substance present in bovine pituitary extract; in 1933 it was established that prolactin is secreted by anterior pituitary. However, prolactin in pure form was isolated as late as in 1971; it is highly homologous with somatotropic hormone (STH) molecule; it occurs in almost all mammals.
Human prolactin is a protein hormone consisting of 198 amino acids; its molecular mass is about 23 kDa.
Prolactin functions in women are as follows:
• together with LH, synchronizing follicle maturation and ovulation;
• maintaining corpus luteum, promoting progesterone production by participating in cholesterol synthesis;
• preparing the breast to lactation;
• regulating the amount and composition of amniotic fluid;
• stimulating milk production in breast alveoli during lactation.
Prolactin is produced by special prolactotroph cells that constitute 11-20% of the total cell population in anterior pituitary. Prolactotroph surface has receptors to dopamine (neuromediator of the medial eminence of hypothalamus); when the receptors bind to dopamine molecules, the secreting cell activity is blocked. The more dopamine there is, the more receptors block prolactotroph activity, and the less prolactin is produced (more dopamine means less prolactin, and vice versa, less dopamine means more prolactin).
NB! Prolactin level is regulated by constant suppression of its synthesis and secretion by hypothalamic dopamine (see Section 3.2.1).
Besides dopamine, other prolactin inhibiting factors are thyroid hormones, gluco-corticoids, GABA, gastrin, gastrin releasing peptide, somatostatin, gonadotropin binding protein, but the effect they produce on prolactin is much less considerable (see Section 3.2, fig. 3.50).