Ontogeny and regulation of luteinizing hormone receptor messenger ribonucleic acid within the ovine corpus luteum.

Although LH regulates corpus luteum (CL) function and LH receptor (LHR) binding has been characterized within ovine CL, changes in LHR mRNA expression have not been documented. The objectives here have been to assess relative amounts of LHR mRNA in ovine CL throughout the estrous cycle and during luteolysis by ribonuclease protection analysis. In experiment 1, LHR mRNA was quantified within CL collected on Days 3, 7, 10, 13, and 16 post-estrus (n = 3, 4, 4, 3, and 4, respectively). LHR mRNA differed throughout the luteal phase (p < 0.01), with higher concentrations found during the midluteal phase (Days 10 and 13) than during the early (Day 3) or late (Day 16) luteal phase (p < or = 0.05). In experiment 2, LHR mRNA content was determined within pools of Day 10 small (n = 4) or large (n = 4) luteal cells. Relative amounts of LHR mRNA were not different (p = 0.1) in small (2.23 +/- 0.22 relative units) vs. large (1.62 +/- 0.22 relative units) luteal cells. In experiment 3, CL were collected at 0, 6, 12, or 24 h after injection of 15 mg prostaglandin F2 alpha) on Day 10 post-estrus (n = 4, 4, 3, and 4, respectively). LHR mRNA content fell during PGF2 alpha-induced luteolysis (p < 0.002), decreasing significantly by 6 h (1.76 vs. 1.10 relative units; p < or = 0.05). By 24 h, levels were approximately 60% of those detected within 0-h controls (1.76 vs. 0.79 relative units; p < 0.05). These results indicate that changes in LHR mRNA during the luteal phase correlates well with previously reported changes in LHR binding. After PGF2 alpha administration, LHR mRNA falls earlier than the reported drop in LHR binding sites occurs.