INTERNAL FEEDBACK OF PROLACTIN IN RAT

The effect on roammotrophic activity of various doses of prolactin implanted in the median eminence (ME) was studied in 102 virgin female rats, each weighing 200±10g. The animals were primed with 9 μg/rat/day of oestradiol for 10 days, and then divided into four equal groups. On the 11th day, three groups were implanted stereotaxically in the MR with prolactin 1, 4, or 16 IU/rat, respectively, and the fourth group, which served as the control, was implanted with empty tubes. On the 16th day, the animals were decapitated, their inguinal mammary glands excised, mounted, stained, and examined in toto.The prolactin-implanted rats showed various degrees of mammary involution, suggesting a dose-response relationship; the controls (Group 4) had well-developed mammary glands. These results indicate the existence of a short internal ‘feedback loop’ for prolactin, similar to that of the other anterior pituitary trophins. An explanation is offered for this ‘negative feedback’ phenomenon of prolactin, based on the existence of a prolactin-releasing factor (PRF) competing with the prolactin-inhibiting factor (PIF). © 1969 S. Karger AG, Basel.