Mechanism of the Postcoital Contraceptive Effect of LH-RH in the Rat. I. Serum Hormone Levels During Chronic LH-RH Administration

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Abstract
Luteinizing hormone (LH)-releasing hormone (200 μg) administered daily over Days 1–7 (D1–7) of pregnancy in the rat, produced a dramatic inhibition of pregnancy. This inhibition was directly correlated with induced “surges” in serum LH over D1–4. Serum follicle stimulating hormone and prolactin were, in general, significantly reduced over this same time period. A 48 h delay in the preimplantation (D3) “surge” in serum estradiol accompanied by a significant reduction in serum progesterone on D3,4,6, and 7 was also observed. The delayed “surge” in serum E2 on D5 and reduction in serum progesterone was correlated with an increase in folliculogensis and significant luteolysis of established corpora lutea, respectively. It is suggested that in the rat LH-RH induces a rise in serum LU which is luteolytic during early pregnancy, and delays the serum estradiol surge necessary for normal implantation.