1999 Volume 46 Issue 4 Pages 563-571
A 57-yr-old female with corticotropinoma showing no Cushingoid stigmata is reported. Basal plasma levels of ACTH measured with immunoradiometric assay and β-endorphin were high, 12.6-15.9pmol/l and 3.5 pmol/l, respectively. Plasma cortisol level and urinary free cortisol excretion were normal, 303-359nmol/l and 171-226nmol/day, respectively. Plasma ACTH markedly increased to 70.5pmol/l with intravenous administration of 100μg CRH. Diurnal rhythm of plasma ACTH was seen, but its level in the night was still high. Plasma ACTH suppression with dexamethasone was insufficient. CRH stimulation after dexamethasone suppression increased plasma ACTH level from 4.4 to 13.7pmol/l. Intravenous administration of 4μg desmopressin increased plasma ACTH from 15.6 to 19.6pmol/l. Oral administration of 16mg lepramide insufficiently decreased plasma ACTH from 7.3 to 5.3pmol/l. However, plasma cortisol responses in these conditions were normal. Postoperative pathological study revealed subtype 1 corticotropinoma immunohistochemically and electron-microscopically. Postoperative basal plasma ACTH decreased to 3.9pmol/l, although plasma cortisol did not change. Diurnal rhythm and dexamethasone suppressibility of plasma ACTH became normal. Plasma sample was chromatographed on a Sephadex G-75 column. The elution profile showed two peaks of ACTH, one of which was compatible with 1-39 ACTH and another with higher molecular weight ACTH which was probably secreted from corticotropinoma. Anomaly in processing of proopiomelanocortin was suspected.