INCREASED LH RECEPTOR MESSENGER-RNA AND EXTENDED CORPUS-LUTEUM FUNCTION INDUCED BY PROLACTIN AND INDOMETHACIN TREATMENT IN-VIVO IN HYSTERECTOMIZED PSEUDOPREGNANT RATS

To assess the effects of prostaglandins and prolactin on corpus luteum function and regression, sterile-mated adult pseudopregnant rats hyst erectomized on day 5 after mating were injected with indomethacin or p rolactin. Daily samples of blood were collected via the tail, from day 12 to day 21, and assayed for serum concentrations of progesterone, 2 0 alpha-dihydroprogesterone and LH, whereafter corpora lutea and the r emainder of ovaries were separated and the tissue content of PGF(2 alp ha), PGE(2) and LH receptor mRNA were measured. Injections of prolacti n (8 iu) s.c. or a low dose of indomethacin (200 mu g kg(-1)) s.c. wer e administered twice a day, beginning on day 13 after mating. Both ind omethacin and prolactin significantly increased serum progesterone con centrations (P < 0.05; n = 8), and extended the period of functional c orpora lutea when compared with controls. Indomethacin, but not prolac tin, lowered the concentration of serum 20 alpha-dihydroprogesterone. In the corpora lutea of indomethacin-treated animals, collected on day 21, both prostaglandins measured were reduced in concentration by 50% or more, compared with controls (P < 0.05; n = 8), whereas prolactin had no effect. Both prolactin and indomethacin treatment caused a subs tantial (tenfold) increase in the concentration of LH receptor mRNA, c onfined solely to the luteal compartment. These findings in vivo provi de further evidence for a luteolytic role of locally synthesized prost aglandins in the rat ovary. Furthermore, prolactin can sustain corpus luteum function by exerting a luteotrophic effect during the late lute al phase, as judged by the stimulation of progesterone synthesis and t he expression of LH receptors.