Hyperprolactinemia with the predominance of high-molecular immunoreactive prolactin: differences in the regulation of the levels of high-molecular and monomer forms in the blood

The effect of drug stimulation of prolactin secretion on the level of its high-molecular (100 kD) and monomeric (23 kD) immunoreactive forms in the blood serum was studied in 5 women with idiopathic hyperprolactinemia with the predominance of the high-molecular form of the hormone. Metoclopramide, a dopamine receptor antagonist, was used for stimulation of prolactin secretion. Fractionation of blood serum immunoreactive prolactin was earned out using gel filtration. A single intravenous infusion of metoclopramide caused a rapid appreciable increase of the total level of immunoreactive hormone, mainly at the expense of its monomer fraction. In contrast to the monomer form, high-molecular prolactin poorly reacted to suppression of the dopaminergic tone. The time course of high- and low-molecular (monomer) forms’ response to metoclopramide differed. The results indicate differences in the regulation of the levels of high- and low-molecular immunoreactive forms of prolactin in the blood of patients with hyperprolactinemia with the predominance of high-molecular hormone and, hence, permit a hypothesis on a different biochemical nature of these two forms and on other than hypophyseal origin of the high-molecular form or its bulk.