[The formation and regulation of the lactotrophic function of the hypophysis in the prenatal period of rat development. I. Prolactin secretion by the hypophysis and the role of dopamine in this process].

Using radioimmunologic assay, we have studied the content of prolactin in the pituitary and its release into general circulation in 18-, 20-, and 22-day-old rat fetuses under normal conditions and after pharmacological block of dopamine receptors. Prolactin was found in the pituitaries of the fetuses from day 5 and in blood serum, from day 18; its levels were progressively increasing up to the end of prenatal development. Administration of haloperidol, an inhibitor of dopamine D2 receptors, to pregnant female increased the level of prolactin in fetus plasma from day 20 and diminished its content in the pituitary gland from day 22. These data provide evidence for secretion of prolactin by the pituitary and sensitivity of lactotrophs to dopamine during prenatal development.