Regulation of Gonadotropin Receptors by Luteinizing Hormone in Granulosa Cells1

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Abstract
In association with luteinization, LH [luteinizing hormone] induces a decrease in the content of receptors for FSH [follicle stimulating hormone] and LH and an increase in that for PRL [prolactin]. To elucidate if the mechanism by which LH regulates its own receptors involved occupancy sites and/or loss of receptors the effects of a luteinizing dose of LH were examined in the preovulatory follicles of immature hypophysectomized rats primed with estradiol and FSH. The measurable LH receptor content declined by 82% 24 h after LH administration. Serum concentration of the hormone declined by 24 h to 1.4% of the concentration measured 2 h after LH administration. Administration of iodinated LH to demonstrate occupancy of sites in vivo, resulted in a decline in the amount of hormone bound in vivo, over a period of time. This decline in occupancy paralleled the decrease in the number of available sites as measured in vitro. A large dose of highly purified h[human]FSH administered in lieu of LH induced luteinization and an associated loss of gonadotropin receptors. Luteinizing doses of LH and FSH induce a loss in gonadotropin receptors by mechanisms other than occupancy.

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