The Effects of Luteinizing Hormone Releasing Hormone (LHRH) in Pregnant Rats 2. Prenidatory Effects and Delayed Parturition

This is the authors' abstract. We don't add key points for this paper.

During the prenidatory period, pregnancy is terminated in rats by doses of 150 µg twice daily (b.i.d.) of LHRH from Days 1–7; a partial effect is seen at 50 µg. Treatment with doses as large as 500 µg b.i.d. of LHRH over Days 1–3 did not result in termination of pregnancy, but the fetuses were smaller in size than controls at autopsy on Day 15. When injected twice on either Day 3 or 4,500 µg of LHRH markedly depressed fetal size; in contrast, the same treatment on Days 1, 2, 5, 6 or 7 was without effect. The depressions in fetal size were explainable on the basis of a 2–3 day delay of implantation following LHRH (500 µg b.i.d.) on Day 3 or 4, which was secondary to retardation of tubal transport (Days 3 and 4) and slowed cleavage (Day 3). Estradiol given on Day 4, but not on Day 3, normalized the effects of LHRH treatment on Day 3 or 4, suggesting that the delay of nidation resulted from estrogen (ovarian) failure. Progesterone had no effect on the delayed implantation. Delayed nidation was followed by postponement of parturition, albeit litters appeared normal.