Luteinizinghormone(LH)isproducedinbothmenandwomenfromtheanteriorpituitaryglandinresponsetoluteinizinghormone-releasinghormone(LH-RHorGn-RH),whichisreleasedbythehypothalamus(1-3).LH,alsocalledinterstitialcell-stimulatinghormone(ICSH)inmen,isaglycoproteinwithamolecularweightofapproximately30.000daltons(4).Itiscomposedoftwononcovalentlyassociateddissimilaraminoacidchains,alphaandbeta(5).Thealphachainissimilartothatfoundinhumanthyroid-stimulatinghormone(TSH),folliclestimulatinghormone(FSH),andhumanchorionicgonadotropin(hCG).Thedifferencebetweenthesehormoneslieintheaminoacidcompositionoftheirbetasubunits,whichaccountfortheirimmunologicaldifferentiation(6-8).ThebasalsecretionofLHinmenisepisodicandhastheprimaryfunctionofstimulatingtheinterstitialcells(Leydigcells)toproducetestosterone.ThevariationinLHconcentrationsinwomenissubjecttothecomplexovulatorycycleofhealthymenstruatingwomen,anddependsuponasequenceofhormonaleventsalongthegonado-hypothalamic-pituitaryaxis.ThedecreaseinprogesteroneandestrADIollevelsfromthepreceedingovulationinitiateseachmenstrualcycle(9,10).Asaresultofthedecreaseinhormonelevels,thehypothalamusincreasesthesecretionofgonadotropin-releasingfactors(GnRF),whichinturnstimulatesthepituitarytoincreaseFSHproductionandsecretion(4).TherisingFSHlevelsstimulateseveralfolliclesduringthefollicularphase,oneofthesewillmaturetocontaintheegg.Asthefollicledevelops,estradiolissecreted,slowlyatfirst,butbyday12or13ofanormalcycleincreasingrapidly.LHisreleasedasaresultofthisrapidestradiolrisebecauseofdirectstimulationofthepituitaryandincreasingGnRFandFSHlevels.Theseeventsconstitutethepre-ovulatoryphase(11).Ovulationoccursapproximately12to18hoursaftertheLHreachesamaximumlevel.Aftertheeggisreleased,corpusluteumisformedwhichsecretesprogesteroneandestrogen-twofeedbackregulatorsofLH(3,10).Thelutealphaserapidlyfollowsthisovulatoryphase,andischaracterizedbyhighprogesteronelevels,asecondestradiolincrease,andlowLHandFSHlevels(12).LowLHandFSHlevelsaretheresultofthenegativefeedbackeffectsofestradiolandprogesteroneonthehypotalamic-pituitaryaxis.