title: Dialyzable free cortisol after stimulation with Synacthen.
abstract: OBJECTIVE
  To compare the changes in free vs. total serum cortisol concentrations after acute stimulation of the adrenal cortex.
  
  
  METHODS
  Paired serum samples of ten individuals taken immediately before and 1 h after stimulation with 250 microg ACTH (1-24) (Synacthen) given i.v. were analyzed. Total cortisol was quantified using liquid chromatography tandem-mass spectrometry with an online sample extraction system and tri-deuterated cortisol as the internal standard. Free cortisol was measured with the same method after equilibrium dialysis. Concentrations of the corticosteroid-binding globulin (CBG) were determined by radioimmuno assay.
  
  
  RESULTS
  Total cortisol increased by a mean of 106% (mean basal cortisol 312 nmol/L (SD 140 nmol/L), stimulated 686 nmol/L (SD 163 nmol/L); p < 0.001, paired t-test for differences); no significant change of CBG concentrations was found (874 nmol/L (SD 179 nmol/L) before stimulation, 869 nmol/L (SD 225 nmol/L) after stimulation). The mean increase of free cortisol was 263% (mean basal free cortisol 20.3 nmol/L (SD 13.2 nmol/L), stimulated 73.8 nmol/L (SD 26.7 nmol/L); p < 0.001) and thus substantially more pronounced compared to the increase of total cortisol (p < 0.01). The ratio of free to total serum cortisol was significantly increased after stimulation (6.1% (SD 1.7%) before stimulation, 10.6% (SD 1.9%) after stimulation; p < 0.001).
  
  
  CONCLUSIONS
  After acute neuroendocrine stimulation of the adrenal cortex the relative increase of free bioactive cortisol concentrations is substantially more pronounced than the increase of total cortisol concentrations.
authors.affiliation: Institute of Clinical Chemistry Ludwig-Maximilians-Universität Munich, Klinikum Grosshadern, 81366 Munich, Germany. Michael.Vogeser@klch.med.uni-muenchen.de
authors.forename: Michael
authors.initials: M
authors.lastname: Vogeser
authors.forename: Josef
authors.initials: J
authors.lastname: Briegel
authors.forename: Reinhart
authors.initials: R
authors.lastname: Zachoval
mesh_terms: D000302:Adrenal Cortex / Q000187:drug effects / Q000378:metabolism; D000328:Adult; D002853:Chromatography, Liquid / Q000379:methods; D003348:Cortisone / Q000097:blood; D003366:Cosyntropin / Q000494:pharmacology*; D003627:Data Interpretation, Statistical; D003956:Dialysis; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000097:blood*; D008297:Male; D013058:Mass Spectrometry / Q000379:methods; D008875:Middle Aged; D013268:Stimulation, Chemical; D014156:Transcortin / Q000378:metabolism
chemical_list: D003366:Cosyntropin; D014156:Transcortin; D003348:Cortisone; D006854:Hydrocortisone