RADIoimmunoassayforthein-vitrodiagnosticquantitativedeterminationofcAMPinhumanplasmaandurine.Thetestcanalsobeusedfornon-clinicalapplicationsinotherBIOLOGicalmaterial.Cyclicadenosin-3",5"-monophosphate(cAMP)servesasasecondmessengerinsignaltransductionofvarioushormones,likeadrenaline,ACTH,LH,FSH,glucagonandcalcitonin.Thehormoneitselfisthefirstmessenger,bindingtospecificmembranereceptorsofhormone-responsivecells.Thisleadstotheactivationofanenzymelocatedattheinnersideofthecellmembrane,calledadenylatecyclase,whichcatalysesthesynthesisofcAMPfromATP.TheincreasedcellularlevelofcAMPinitiatestheactivationofproteinkinases.
ThedeterminationofcAMPinurine(orplasma)hasbecomemoreandmoreimportantintheclinicalassessmentofparathyroidfunctions.Theparathyroidhormone(PTH)stimulatesthesynthesisofcAMPintherenalcortexandanincreasedsecretionofcAMP.ThenephrogeniccAMPisaspecificMarkerofcirculatingPTH:90%ofpatientswithhyperparathyroidismshowincreasedlevelsofnephrogeniccAMP.ThedeterminationofnephrogeniccAMPisalsosignificantforthedifferentialdiagnosisofhypercalcemia.
UrinarylevelsofcAMPsupportthediagnosisofhypoparathyroidismandpseudohypoparathyroidism:TheadmiNISTrationofPTHtopatientswithpseudohypoparathyroidismdoesnotleadtoanincreasedcAMPsecretion,whichisindicativeofadefectiveadenylatecyclaseintherenalcortex.
TotalurinarycAMPlevelscomprisethenephrogeniccAMPandtheplasmacAMPwhichisnotresorbedinthekidneys.InmostcasesthedeterminationoftotalurinarycAMPissufficient,becausetheconcentrationofplasmaticcAMPismoreorlessconstant.