Prostaglandin F2 alpha receptors in the early bovine corpus luteum.

Since the early CL (< or = 4 days after ovulation) does not regress after injection of PGF2 alpha, this study was designed to determine whether number or affinity of PGF2 alpha receptors was lower in the early as compared with the midstage CL. Heifers were randomly assigned to have ovaries removed on Day 2, 4, 6, or 10 (n = 4 heifers per day; Day 0 = day of ovulation). Plasma progesterone concentrations and the weight and size of the CL increased from Day 2 to 6, indicating normal CL development. Plasma membranes from individual CL were evaluated for PGF2 alpha receptor concentration and affinity by Scatchard analysis. CL from each of the 4 days of the estrous cycle were not different with respect to PGF2 alpha receptor concentration (number per microgram of plasma membrane protein) and affinity. To examine tissue specificity, PGF2 alpha binding was evaluated in 12 organs or tissues. High-affinity PGF2 alpha receptors were found in the CL and adrenal medulla but not in granulosa cells or other tissues. In conclusion, a single class of high-affinity PGF2 alpha receptors was present within the bovine CL by 2 days after ovulation; therefore the reported lack of responsiveness to PGF2 alpha in the early CL was not attributable to a deficiency of high-affinity PGF2 alpha receptors.