Luteinizing hormone beta-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.

Abstract

Amounts of mRNA for luteinizing hormone (LH) beta-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 beta-subunit mRNA was evaluated by Northern transfers, using a specific bovine LH beta 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 beta mRNA amounts increase after day 12, reaching a value of approximately 12-fold by E + 25. When correlated with serum and pituitary LH amounts, it is observed that the amounts of beta mRNA increase in a fashion parallel to serum and pituitary LH concentrations through the time E + 5. After this time, LH beta mRNA amounts continue to increase despite a dramatic fall in both serum and pituitary LH. These results suggest that LH beta mRNA amounts are regulated during the LH preovulatory surge.