Masked gonadotropin-binding sites in human corpora lutea during menstrual cycle and pregnancy

To evaluate the possible existence of masked receptors for luteinizing hormone (LH)/human chorionic gonadotropin (hCG) in the human corpus luteum, we examined the effect of neuraminidase pretreatment on the specific binding of ( 125 I)hLH to luteal particulates obtained from 11 patients during the menstrual cycle and 4 patients during early pregnancy. The pretreatment with neuraminidase significantly enhanced the specific binding of hLH to corpora lutea at the different stages of the luteal phase. Scatchard analyses revealed that neuraminidase increased the number of LH binding sites without altering the affinity for LH. Furthermore, the specific binding of hLH to human corpora lutea during pregnancy significantly increased after the pretreatment with neuraminidase. The data suggest that distinct populations of receptors for LH/hCG are masked within the human luteal cells.