Role of Pituitary LH and Placenta in Luteal Progesterone Production and Maintenance of Pregnancy in the Rat
It is now well-established that neutralization of circulating LH using specific antiserum leads to termination of pregnancy in the rat (1–3). In our extensive investigations, we demonstrated that LH antiserum is effective when administered from day 1–8 or any day between 8 and 11 (1,3). Neutralization of LH is effective even at midnight of day 11, but not at 10 a.m. on day 12, indicating a sharp ‘cut off’ point. The observed termination of pregnancy is accompanied by profuse vaginal bleeding 36 to 48 hrs after antiserum administration. Plasma progesterone levels drastically fall within a short period of neutralizing LH (4). This indicates that LH is essential for production of progesterone at this time of pregnancy. The effects of LH antiserum on pregnancy have been amply confirmed by other investigators (5–7). Morishige and Rothchild (5) extended these studies to earlier period of pregnancy and demonstrated that LH dependency sets in between day 6 and 8, simultaneously with the loss of dependency on pituitary prolactin. To investigate the mode of action of LH, Gibori et al utilized the LH antiserum treated rat model system (8). They demonstrated that testosterone implants can maintain pregnancy, in such rats. Further Gibori and Keyes have provided significant evidence that testosterone administered is converted to estrogen, which in turn maintains progesterone production in the pregnant rat. The rat corpus luteum contains high concentrations of estrogens during pregnancy (9, 10) and exogenous estrogen stimulates luteal growth and progesterone secretion in hypophysectomized-hysterectomized pregnant rats (11, 12). Intraovarian bursal estrogen implants also seem to maintain luteal functionality as judged by progesterone secretion, during days 10 and 11 of pregnancy (13). Thus at the present time it seems that the luteal progesterone production becomes dependent on pituitary LH and placental luteotropin by day 8 of pregnancy. The present series of investigations were undertaken to elucidate the contribution of the placenta and its potential to sustain steroidogenesis in the absense of LH.
KeywordsProgesterone Production Luteal Function Progesterone Secretion Synthetic Progestin Serum Progesterone Level
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