Radioimmunoassay of Serum Levels of Luteinizing Hormone during the Cycle and Early Pregnancy in Ewes ∗

Abstract

Summary

Development of a radioimmunoassay for ovine luteinizing hormone (LH) has allowed determination of levels of LH in small sequential aliquots of serum obtained from ewes throughout the estrous cycle and during the first 20 days of gestation. Elevated levels of LH were noted on the day of estrus in cyclic ewes. When ewes were checked for estrus at hourly intervals and blood was collected every 4 hr, the LH peak (mean = 47 mμg/ml) was observed from 0–12 hr after the onset of estrus. The LH levels at other stages of the cycle were very low or nondetectable (< 0.5 mμg/ml). The levels in ewes during the first 20 days and at day 40 of gestation were also very low or nondetectable. This finding was discussed in light of existing data suggesting that LH is responsible for maintenance of the corpus luteum of gestation. Serum content of LH of both males and females in various endocrinologic states was also reported.