Inhibition by Hypothalamic Prolactin Implants of Prolactin Secretion, Mammary Growth and Luteal Function

Abstract

Implantation of prolactin into the median eminence of mature intact and ovariectomized rats resulted in increased hypothalamic content of prolactin inhibiting factor (PIF), reduced pituitary prolactin concentration, and pituitary weight, and marked regression of the mammary glands. The ovaries of the intact prolactin-implanted rats were characterized by well-developed follicles and relatively few large corpora lutea, whereas the ovaries of the sham-operated rats had large corpora lutea characteristic of pseudopregnancy. These observations suggest that implanted prolactin inhibits pituitary prolactin synthesis and release by directly increasing hypothalamic PIF secretion.