The Roles of Prolactin and Testosterone in the Development and Function of Granulosa Lutein Tissue in the Rat1

Abstract

The luteotropic roles of prolactin and testosterone (or estradiol formed in luteal tissue) were investigated in hypophysectomized rats with homografts of granulosa lutein tissue. Using this approach, we could determine the effects of prolactin independently of estrogen, since granulosa lutein tissue does not produce estrogen de novo under these conditions. Luteinizing granulosa cells were expressed from the ovaries of immature pregnant mare's serum gonadotropin-primed Fischer 344 rats 6 h after injection of human chorionic gonadotropin. The cells were transplanted beneath the kidney capsule of adult, hypophysectomized, ovariectomized Fischer 344 recipients, which were treated with hormones daily for 12 or 14 days. In rats without treatment (no hormones, n = 3) and in rats treated with only testosterone (Silastic capsule, n = 6), only small amounts of luteal tissue (less than 5 mg/rat) were found and serum progesterone remained at low concentrations (10 ng or less) throughout the experiment. In contrast, in rats treated either with ovine prolactin (300 micrograms/day, n = 10) or with the combination of prolactin and testosterone (n = 12), serum progesterone increased to 43 ng/ml by Day 8. Beyond Day 8, serum progesterone continued to rise in rats treated with the combination of prolactin and testosterone to reach a mean value of 87 ng/ml by Day 14, and mean homograft wet weight was 49 mg/rat; in rats treated with only prolactin, serum progesterone decreased to 25 ng/ml by Day 14 and homograft wet weight was lower (24 mg/rat). Prolactin and testosterone together stimulated more homograft aromatase activity in vivo than did prolactin alone, but the in vitro production of progesterone was not different.(ABSTRACT TRUNCATED AT 250 WORDS)

Luteal Function: The Estrous Cycle and Early Pregnancy

“…This luteotrophin maintains LH receptor numbers and the capacity of luteal cells to secrete estradiol. Prolactin (or prolactin-like compounds) is sufficient to maintain luteal function for 10 days after ovulation; however, later increases in luteal weight and progesterone secretion require both prolactin and intraluteal estradiol [56,131]. Thus, pregnancy-associated increases in luteal function in the rat are due to a synergistic action of prolactin-like luteotrophins and estradiol.…”

Activation of PKC δ in the Rat Corpus Luteum during Pregnancy

“…Activation of PKC Isoforms by PRL-During the second half of pregnancy, when we detect activated PKC ␦, the rat corpus luteum is maintained exclusively by the combined actions of intraluteal E 2 , aromatized from androgens provided by the placenta (1), and PRL-like hormones such as the placentaderived rPL-1 (1,20). We have found that rPL-1 treatment of luteinized granulosa cells promotes phosphorylation of Stat 3 on tyrosine 705 and serine 727 and induction of relaxin mRNA expression, 2 a major product of the rat corpus luteum in the second half of pregnancy (21).…”

“…The ␦ isoform can be distinguished from the other isoforms by the striking increase of both PKC ␦ mRNA and protein levels in corpora lutea in the second half of pregnancy (19). The rat corpus luteum is maintained in the second half of pregnancy by the combined actions of intraluteal E 2 and PRL-like hormones such as the placenta-derived rPL-1 (1,20). We have found that rPL-1 treatment of luteinized granulosa cells induces phosphorylation of Stat 3 on both tyrosine 705 and serine 727 and induction of relaxin mRNA expression, 2 a major product of the rat corpus luteum in the second half of pregnancy (21).…”