hGHisapolypeptidehormone(molecularweight21,500Da)producedbytheacidophilcellsoftheanteriorpituitaryunderthecontroloftwomainsubstancesfromthemedianeminence:Growth-hormoneReleasingFactor(GRF)andaninhibitoryagent,somatostatin.Dopaminergic,adrenergicandSEROtoninergicneuroendocrinepathwaysalsoplayanimportantroleinthecontrolofhGHsecretion.ExcitatorystimuliofhGHsecretionincludehypoglycemia,exercise,fasting,mealswithahighproteincontent,deepsleep,stress,glucagon,LDopa,aminoacids,etc.

Inhibitorystimuliincludeglucose,cortisol,hGHandfreefattyacids.Becauseofitsshortplasmahalflife(±25minutes)andofthefrequentexcitatoryorinhibitorystimuli,hGHdisplaysfrequentandlargevariationsofconcentrationinserum.OneofthemainphysiologicalfunctionsofhGHistoactontheliverandothertissuestoproduceSomatomedins,whichinturninducegrowthbydirectactionontargettissues.IncontrasttohGH,theconcentrationofsomatomedininserumiskeptstablebyvirtueofbeinglargelyboundtocirculatingplasmaproteins.

ClinicalapplicationofGrowthhormomeIRMA(CT)

• GrowthretardationhGHhyposecretionisoneofthevariouscausesofsmallstatureinchildren.SerumhGHmeasurementwithahighlysensitiveassay,especiallyfollowingaprovocativestimulus(absenceofresponse),isanimportantwaytoestablishthisdiagnosisbecausethisgroupofpatientscanbetreatedbyadmiNISTrationofhGH.
• HypopituitarismSerumhGHmeasurementisalsoanindexofpituitaryfunctionwhenhypopituitarism(eitheridiopathicorduetotumourandsurgery)issUSPected.
• GigantismandacromegalySerumhGHmeasurement,especiallyfollowingaprovocativeinhibitorytest(absenceofresponse),isanimportantwaytoestablishthediagnosisofhGHhypersecretionduetoacidophilicpituitarytumour.Thisresultsingigantisminchildrenandacromegalyinadults.BothofthesedisordersmaybetreatedbysurgeryorrADIation.