The progesterone-sensitive period of rat pregnancy: some effects of LHRH and ovariectomy.

SummaryLHRH (0.5 mg x 2) on Day 7 of pregnancy is followed by a profound, ephemeral reduction in circulating progesterone, but not by fetal resorption; a similar decrease in progesterone follows the same treatment on Day 9, but it is associated with termination of pregnancy in most animals. These effects appear to result from differential sensitivity to progesterone deprivation, since delay of progestational support for varying periods following ovariec-tomy on Day 7 produces fewer indications of resorptions than on Day 10. A slight, but significant, reduction in progesterone after treatment on Day 13 would appear inadequate to affect continuation of the pregnancy.