Change in concentrations of luteinizing hormone subunit messenger ribonucleic acids in the estrous cycle of beef cattle

Changes in the concentrations of LH subunit messenger ribonucleic acids (mRNAs) and in the LH content of the anterior pituitary of beef cattle were studied during the estrous cycle. Japanese beef cows were classified according to the expected day of the estrous cycle: stage I (early-luteal phase, days 1–4; day 1=day of ovulation), stage II (early-mid-luteal phase, days 5–10), stage III (late-mid-luteal phase, days 11–17) and stage IV (follicular phase, days 18–20), according to the morphology of the ovaries. The anterior pituitaries of the cows were collected and the levels of α and LHβ subunit mRNAs were determined by slot–blot analyses. The LH content of the anterior pituitary was measured by radioimmunoassay. The level of α subunit mRNA in the pituitary of cows was highest in stage I and decreased significantly by stage II (P<0.05); thereafter it tended to increase. The level of LHβ subunit mRNA did not change significantly during the estrous cycle. The LH content of the pituitary of cows was low in stage I and tended to increase by stage II, then to decrease from stage II to III, and to increase significantly from stage III to IV (P<0.05). These results suggest that the highest levels of gene expressions of α subunit in the anterior pituitary occur in the early-luteal phase of beef cows, while the LH content is increased most in the follicular phase. The enhanced gene expressions of common α subunit in the early-luteal phase could be important in replenishing the bovine anterior pituitary with LH, which is depleted of hormone by the LH surge or the enhanced pulsatile release.