Changes in Serum LH, Progesterone, and Specific Binding of 125I-hCG to Luteal Cells During Regression and Development of Bovifle Corpora Lutea1

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Abstract
Changes in concentrations of LH and progesterone in serum and specific binding of 125I-hCG to crude membrane preparations of luteal cells were examined during spontaneous regression (Group 1), prostaglandin-induced regression (Group 2), and growth (Group 3) of bovine corpora lutea (CL). Specific binding of 125I-hCG (presumably by the LH receptor) to luteal homogenates was validated using Scatchard analysis and shown to be specific for LH/hCG with high affinity (Ka = 2.18 ± 0.76 x 1010 M-1). All cattle had estrous cycles synchronized with a synthetic prostaglandin F2α, cloprostenol (PG). Group 1 had ovaries removed on Day 17, 18, 19, on estrus, or 24 h after estrus. Group 2 had ovaries removed at 0, 12, 24, 48, 60, or 72 h after PG. Group 3 had ovaries removed at 5, 7, 9, 11, 13, or 15 days after PG. Blood samples were taken from all animals at 8 h intervals up to time of ovariectomy for measurement of serum progesterone and LH and at 2 h intervals around estrus to determine time of preovulatory LH surge. Data from heifers in Group 3 were grouped for analysis according to days after preovulatory LH surges.