Serum Progesterone in Pregnant Rats with Ectopic or in situ Corpora Lutea: Correlation Between Amount of Luteal Tissue and Progesterone Concentration1, 2
Serum progesterone was measured by radioimmunoassay on Days 7, 9, 11, 13, 15, and 16 of pregnancy in three groups of rats. 1) rats with two intact ovaries, 2) rats with one intact ovary (unilaterally ovariectomized the evening of proestrus) and 3) rats with ectopic corpora lutea and a single ovary from which in situ corpora lutea were removed on Day 6 of pregnancy. Progesterone concentrations in the three groups were significantly different (P<0.05) from one another on each day of pregnancy with the exception of Day 13 on which progesterone levels in groups 1 and 2 were not significantly different. Mean progesterone concentrations (ng/ml) and total luteal weights (mg) on Day 16 were respectively 126 ng/ml, 59 mg (group 1), 68, 27 (group 2) and 28, 15 (group 3). A significant positive correlation (P<0.01; r = 0.97; n = 21) was found between total luteal weight and serum progesterone concentration on Day 16 of pregnancy.