Depletion of Prolactin-Inhibiting Activity of Rat Hypothalamus by Estradiol or Suckling Stimulus11

Abstract

Previous studies from this laboratory have shown that the hypothalamus contains a factor (s) which inhibits prolactin synthesis and release in vitro. The present experiments were undertaken to determine whether certain prolactin-releasing agents acted by depressing hypothalamic production of “prolactin-inhibiting factor” (PIF). Anterior pituitary incubated in a Dubnoff shaker at 37 C for 2 hr in a medium containing hypothalamic extract from rats injected with estradiol, or from suckled postpartum rats, released 114 and 133 % more prolactin, respectively, than similar pituitaries incubated with hypothalamic extract from control cycling rats. Hypothalamic extract from the estradiol- treated or suckled rats had no significant effect on prolactin release by incubated anterior pituitary, whereas hypothalamic extract from control cycling rats inhibited prolactin release by some 50%. These results indicate that estradiol and suckling can deplete the hypothalamus of PIF, thus removing hypothalamic inhibition to pituitary prolactin release. (Endocrinology75: 377, 1964)