A new in vitro model system for the study of luteinizing hormone receptor down-regulation

The overall goal of our research is to elucidate the cellular mechanisms involved in the process of luteinizing hormone (LH)-stimulated down-regulation of the LH receptor. Towards this end, we became interested in determining whether cultured granulosa cells could be used as a physiologic model system to study this important process. In this report, we show that a very brief exposure (2 min) to physiologic concentrations of LH causes down-regulation of the LH receptor in granulosa cells cultured in serum-free medium. These data represent the first in vitro demonstration of down-regulation of the LH receptor in the granulosa cell. Furthermore, the dose dependency and kinetics of down-regulation of the LH receptor in vitro, as described here, are very similar to those reported for LH receptor down-regulation in vivo. Thus, this granulosa cell culture system is a powerful new model for studying the biochemical events involved in LH receptor down-regulation.