It is common opinion that maximal activation of luteinizing hormone (LH)-dependent steroidogenic signal occurs at <1% of human LH/choriogonadotropin (hCG) receptor (LHCGR) occupancy. This effect would be a consequence of an excess of receptors expressed on the surface of theca cells, resulting in a pool of LHCGRs remaining unbound (spare). This concept was borrowed from historical pharmacological studies, when discrepancies between ligand-receptor binding and dose-response curves of cAMP were evaluated by treating mouse or rat Leydig cells with hCG in vitro. Recent findings demonstrated the specificity of LH- and hCG-dependent effects, receptor heterodimerization, and differing behaviors of rodent versus human gonadotropin-responsive cells, which may help to revise the 'spare' LHCGRs concept applied to human ovarian physiology and assisted reproduction.
'Spare' Luteinizing Hormone Receptors: Facts and Fiction / Casarini, Livio; Santi, Daniele; Simoni, Manuela; Potì, Francesco. - In: TRENDS IN ENDOCRINOLOGY AND METABOLISM. - ISSN 1043-2760. - 29:4(2018), pp. 208-217. [10.1016/j.tem.2018.01.007]