Luteinizing Hormone β-Subunit mRNA Amounts Increase During the Preovulatory Surge of Luteinizing Hormone in the Ewe: The Highest Levels are Observed at the Completion of the Peak

Amounts of mRNA for luteinizing hormone (LH) β-subunit were assessed during selected times in the normal estrous cycle of sheep. These times spanned the luteal phase through the preovulatory LH surge, and included groups designated as: (i) day 12 of the cycle (day 12); (ii) 24 hr before the onset of the expected behavioral estrus (E − 24); and (iii) 5, 15, and 25 hr after the onset of behavioral estrus (E + 5, E + 15 and E + 25). These groups were characterized by criteria such as serum and pituitary LH concentrations, serum progesterone, and ovarian morphology. Specific LH β-subunit mRNA was evaluated by Northern transfers, using a specific bovine LH β cDNA probe. Slopes were determined using a linear regression analysis and then expressed as fold stimulation relative to the values for the day 12 group. The results indicate that LH β mRNA amounts increase after day 12, reaching a value of ∼ 12-fold by E + 25. When correlated with serum and pituitary LH amounts, it is observed that the amounts of β mRNA increase in a fashion parallel to serum and pituitary LH concentrations through the time E + 5. After this time, LH β mRNA amounts continue to increase despite a dramatic fall in both serum and pituitary LH. These results suggest that LH β mRNA amounts are regulated during the LH preovulatory surge.