The luteotrophic effects of estradiol and prolactin in the absence of LH in the hysterectomized, pseudopregnant rat.

Abstract The ability of estradiol and prolactin to substitute for LH as luteotrophins was investigated in Day 5 (Day 1 = ovulation)-hysterectomized pseudopregnant (PSP) rats. All animals received either a sc injection of oil, 1 μg estradiol (E-1), or 150 μg prolactin (PRL) on Day 9 in combination with either a normal horse serum (NHS) or LH antiserum (LHAS) injection. The ability of oil, E-1, or PRL to maintain luteal function was assessed by monitoring serum progesterone levels through Day 12 and their direct effects on the ovary monitored by measuring luteal and extra-luteal ovarian tissue concentrations of estradiol and progesterone on Day 12. NHS treatment in combination with either oil, E-1, or PRL maintained elevated serum progesterone levels through Day 12 of PSP. LHAS/oil-treated rats underwent luteolysis while E-1 and PRL effectively maintained luteal function in LHAS-treated animals. PRL raised luteal and extraluteal ovarian estradiol concentrations compared to oil/NHS-treated controls and LHAS/oil-treated rats. E-1 induced an intraluteal rise in estradiol levels in LHAS-treated rats. While luteal progesterone concentrations fell following oil/LHAS treatment, E-1 and PRL effectively counteracted this LHAS-induced fall. The results of these studies indicate that (i) E-1 and PRL can effectively replace LH as luteotrophins during PSP in the rat and (ii) that PRL and E-1 effectively maintain luteal levels of estradiol and progesterone following LH deprivation. It is suggested that E-1 and PRL may exert their luteotrophic actions by either an E-1-induced increase in PRL which, in turn, acts on the luteal cells to increase intraluteal estradiol concentrations, or by a direct effect of E on the corpus luteum to bypass the requirement for LH.