Variation in Progesterone Content of the Bovine Corpus Luteum of the Estrual Cycle

Abstract

Corpora lutea were studied at 3, 5, 7, 9, 11, 13, 15, 17 and 19 days after estrus in virgin dairy heifers to determine changes in progesterone, 4-pregnene-20 β-0l 3-one, cholesterol, DNA, RNA and percent type I and II (Foley and Greenstein, 1958) luteal cells. For each day from 7 through 17, two corpora lutea were obtained at the same stage of two different estrual cycles from each of two heifers via supra vaginal incision. For days-3, -5 and -19, corpora lutea were obtained at slaughter either from the above heifers or from similar heifers. An analysis of variance on the values for day-7 through -17 showed a significant increase in progesterone concentration and content (P<.01), 4-pregnene-20 β-ol-3-one concentration (P<.05) and percent type I and II cells (P<.01) to day-15 followed by a significant drop at day-17. Free cholesterol concentration paralleled approximately the increase in progestogen concentration to day-15, but continued to increase at day-17 after the progestogens had dropped. The concentratration of DNA and RNA did not differ significantly among days-7 through -17, but the ratio of RNA to DNA decreased significantly (P<.05) from day-13 to day-17. Corpora lutea weights did not differ significantly from day-7 through -17, with regressive changes beginning at day-17. The percent dry weight of luteal tissue increased significantly from day-7 through -17 and appeared to be progressive throughout the estrual cycle. Significant heifer repeatabilities were found for corpus luteum weight (0.54), 4-pregnene-20 β-ol-3-one concentration (0.65) and DNA concentration (0.90). It would appear that the functional activity of the bovine corpus luteum of the estrual cycle increases to about day-15 and then declines as shown by a decrease in corpus luteum weight, progestogen concentration and content, RNA/DNA and percent type I and II luteal cells.