Identification of luteinizing hormone receptor binding inhibitor in bovine corpora lutea

Abstract

A 7000 g supernatant, obtained during the purification of luteinizing hormone (LH) receptor from bovine corpora lutea homogenate, was concentrated by ultrafiltration. The filtrate, containing < 50,000 molecular weight material, exhibited LH receptor binding inhibitor (LH-RBI) activity. The filtrate was ultrafiltered sequentially through Amicon PM-10, PM-30 and UM-2 filters to yield a LH-RBI-containing fraction in the higher molecular weight range of 30,000-10,000 and a LH-RBI-containing fraction in the lower molecular weight range of 10,000-1000. The higher molecular weight LH-RBI fraction was purified on Sephadex G-25 and the lower molecular weight LH-RBI fraction was purified on Sephadex G-50. Both the high- and the low-molecular-weight LH-RBI species inhibited the binding of 125I-labeled human chorionic gonadotropin (hCG) to bovine corpora lutea and to rat Leydig cell membrane receptors. Similarly, the production of testosterone by hCG-stimulated rat Leydig cells was inhibited in a dose-response manner by both the high- and the low-molecular-weight LH-RBI species. The LH-RBI activity in the low-molecular-weight species was stable at 4 degrees C for up to 6 months and at temperatures up to 90 degrees C for 15 mins, whereas the LH-RBI activity of the high-molecular-weight species was stable at 4 degrees C for 15 months and unstable at 60 degrees C after 15 min. The 7000 g supernatant provided a much-needed source to obtain larger than previously reported quantities of LH-RBI for isolation as well as for structure and function studies.

Studies on LHRBI of Sheep Corpora Lutea—A Preliminary Report on In Vivo Administration to Rhesus Monkeys

“…The presence of high and low molecular weight species was found by Rathnam et al, (6) in the same bovine corpora lutea. These studies confirm our earlier findings on the existence of LHRBI-like material in corpora lutea of porcine (13), human (3) and sheep (4) ovaries.…”

“…It was soon followed by other reports demonstrating the association of such an activity with corpora lutea of porcine (2), human (3), sheep (4) and bovine (5,6) ovaries.…”