Pituitary a-Subunit Messenger Ribonucleic Acid Remains Elevated during the Latter Stages of the Preovulatory Luteinizing Hormone Surge*

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Abstract
In this study, pituitary .alpha.-subunit mRNA [messenger RNA] amounts were assessed during the latter stages of the preovulatory LH [luteinizing hormone] surge in the normal cycling ewe. The times chosen were 15 and 25 h after the onset of behavioral estrus, designated E+15 and E+25. These mRNA values were correlated with pituitary and serum LH concentrations to assess the possible role of subunit synthesis during these times of the cycle, and then compared to values obtained from hybridizations of RNA from animals in other groups representing defined stages of the cycle. One of these groups included animals during the midluteal phase (day 12), whose amounts were assigned a value of 1. The amounts of .alpha.-subunit mRNA in E+15 and E+25 groups, as measured by translations and cDNA [clonal DNA] hybridizations, were approximately 10-fold higher than the day 12 values and were roughly similar to those observed in a group examined 5 h after estrus. It is evident that the .alpha.mRNA levels are not only elevated during the LH surge, but also remain high at a time when both serum and pituitary LH concentrations have fallen dramatically, suggesting the involvement of changing mRNA amounts in the feedback systems associated with the maintenance of pituitary and serum gonadotropin amounts.

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