Introduction: LH and hCG act on the same receptor (LHCGR), have different half-lives and in vivo biopotency. It is not known whether they elicit the same cellular and molecular response. The aim of this study was to compare the kinetics of cAMP response to recombinant LH and hCG.
Design: In COS-7 cells permanently expressing the human LHCGR (COS-7/LHCGR) we evaluated LH and hCG dose-response curves, by measuring total cAMP after 3 h of incubation. We then evaluated the time-course of intracellular cAMP production in the presence of ED50 doses of LH and hCG over 3 h. Finally we evaluated the long-term response to LH and hCG by exposing human primary granulosa lutein cells (hGLC) to ED50 doses over 12 h. All incubations were performed in the presence of IBMX.
Results: In COS-7/LHCGR cells, we observed significantly different ED50 for LH (475.75±137.33 pM, mean±S.D.) and hCG (101.75±44.63 pM) (MannWhitneys U-test, P=0.029; n=4). Maximal LH stimulation of intracellular cAMP, about 50 fold over control, reached a plateau in 10 min, while maximal hCG stimulation at similar levels was attained only after 1 h (Anova; P<0.05; n=3). In hGLC continuous exposure to LH and hCG resulted in a repetitive, pulsatile increase of intracellular cAMP with peaks every 34 h and significantly higher levels of stimulation in the presence of hCG vs LH (Anova; P<0.05; n=3).
Conclusions: Equimolar concentrations of human recombinant LH and hCG result in significantly higher in vitro biopotency of hCG (about 5-fold). Equipotent concentration (ED50) of LH and hCG stimulate a faster response to LH within the first 3 h, but a quantitatively higher response to hCG over 12 h. hGLC respond to constant LH/hCG stimulation in a pulsatile fashion, suggesting a novel control of gonadotropins action at the receptor level.