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A comparison of the naloxone test with the insulin stress test in patients following transsphenoidal surgery
Author(s) -
McAllister As,
McCance Dr,
Hadden Dr,
Bell Pm,
Hilary Leslie,
B. Sheridan,
A. B. Atkinson
Publication year - 1999
Publication title -
clinical endocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.055
H-Index - 147
eISSN - 1365-2265
pISSN - 0300-0664
DOI - 10.1046/j.1365-2265.1999.00670.x
Subject(s) - endocrinology , medicine , immunoradiometric assay , radioimmunoassay , (+) naloxone , insulin , hypothalamic–pituitary–adrenal axis , hydrocortisone , hormone , opioid , receptor
OBJECTIVE To study the reliability of the naloxone test in assessing the hypothalamic‐pituitary‐adrenal (HPA) axis in patients following transsphenoidal pituitary surgery, by comparison with the insulin stress test (IST). Also, to establish a normal range for the response to naloxone in healthy controls. DESIGN All patients had the IST performed, soluble insulin 0.1–0.3 U/kg (usually 0.15 U/kg) being administered intravenously, followed by venous sampling for plasma glucose and serum cortisol at 0, 15, 30, 45, 60, 75 and 90 minutes. Naloxone (125 μg/kg body weight) was similarly administered to all patients 6 days later, with sampling at −15, 0, 15, 30, 45, 60, 90 and 120 minutes for plasma glucose, serum cortisol and plasma ACTH. The naloxone test was also performed on control subjects using an identical protocol. SUBJECTS Twenty patients (11F/9M) aged 48.8 ± 2.8 years (mean ± SE) 4–6 weeks following transsphenoidal pituitary surgery. Twelve normal healthy control subjects (6F/6M) aged 31.5 ± 3.0 years. MEASUREMENTS Serum cortisol was measured by radioimmunoassay and plasma ACTH by immunoradiometric assay. RESULTS Adequate hypoglycaemia (≤2.0 mmol/l) was achieved in all patients. Peak cortisol was >550 nmol/l in 17 subjects (range 572–867 nmol/l) and a subnormal response observed in 3 (peak cortisol 163–498 nmol/l). In the 17 patients with a normal cortisol response to hypoglycaemia the response to naloxone was extremely variable, with serum cortisol falling in 4 and an increment of ≤100 nmol/l in 6 others. In the 3 patients who failed the IST, two responded to naloxone and one did not. In normal controls, 3 of the 12 had little or no response to naloxone. CONCLUSIONS As the naloxone test fails to produce a response in all normal subjects it is impossible to define a ‘normal’ response. The numerous discrepancies with the IST in patients are further evidence of the test's lack of reliability in assessing the HPA‐axis and it is consequently not a viable alternative to traditional dynamic methods such as the IST.