title: Profile, mean residence time of ACTH and cortisol responses after low and standard ACTH tests in healthy volunteers.
abstract: OBJECTIVE
  No consensus exists until now about the suitable dose of tetracosactin in the ACTH stimulation test for detecting adrenal insufficiency. Our aim was to characterize both the ACTH(1-24) and the cortisol profiles after standard high-dose test (250 microg) (HDT) and low-dose test (1 microg) (LDT) in healthy subjects in order to provide a deeper knowledge about the relationship between stimulus and response.
  
  
  METHODS
  ACTH tests were performed in 10 healthy volunteers (five men, five women) with at least 1 week of difference.
  
  
  METHODS
  Plasma ACTH(1-24) and ACTH(1-39) and serum cortisol were measured before tetracosactin i.v. injection and at 5, 15, 30, 45, 60, 75 and 90 min after stimulus. Area under the curve (AUC) of ACTH(1-24) and cortisol, as well as mean residence time (MRT) for ACTH(1-24) were calculated in both tests.
  
  
  RESULTS
  Elimination of ACTH(1-24) was faster in HDT than in LDT (MRTs of 0.14 vs 0.37, respectively, P = 0.008), but plasma concentrations were higher up to 60 min cortisol production in HDT reaching a higher maximum concentration (Cmax: 1144 vs 960 nmol/l) but delayed in time (75 vs 52.5 min). No significant relationship was observed between AUC or Cmax of ACTH(1-24) and AUC, Cmax and increment of cortisol in any of the tests. However, a negative correlation of basal cortisol values was observed with relative cortisol increment (HDT: r = 0.77 P = 0.009; LDT: r = 0.94 P < 0.0001), but not so with Cmax (HDT: r = 0.22 P = 0.55; LDT: r = 0.57 P = 0.09).
  
  
  CONCLUSIONS
  The elimination rate of ACTH in healthy volunteers was significantly lower in LDT than in HDT, but cortisol production rate appears to be identical in both tests, so that a maximum adrenal stimulation seems to exist. The use of LDT may be more adequate, although data from patients need studying.
authors.affiliation: Department of Clinical Chemistry, Hormone and Genetics Unit, IDIBELL-Hospital Universitari de Bellvitge, Barcelona, Spain. palia@csub.scs.es
authors.forename: P
authors.initials: P
authors.lastname: Alía
authors.forename: C
authors.initials: C
authors.lastname: Villabona
authors.forename: O
authors.initials: O
authors.lastname: Giménez
authors.forename: E
authors.initials: E
authors.lastname: Sospedra
authors.forename: J
authors.initials: J
authors.lastname: Soler
authors.forename: M A
authors.initials: MA
authors.lastname: Navarro
mesh_terms: D000304:Adrenal Cortex Function Tests / Q000592:standards*; D000309:Adrenal Insufficiency / Q000175:diagnosis; D000324:Adrenocorticotropic Hormone / Q000097:blood*; D000328:Adult; D019540:Area Under Curve; D003366:Cosyntropin / Q000097:blood; D004334:Drug Administration Schedule; D005260:Female; D006728:Hormones / Q000097:blood; D006801:Humans; D006854:Hydrocortisone / Q000097:blood*; D008297:Male; D008657:Metabolic Clearance Rate
chemical_list: D006728:Hormones; D003366:Cosyntropin; D000324:Adrenocorticotropic Hormone; D006854:Hydrocortisone