Immunoglobulins of patients with Cushing's syndrome due to pigmented adrenocortical micronodular dysplasia stimulate in vitro steroidogenesis

The putative stimulation of adrenal steroid production by immunoglobulins (Igs) of five patients with pigmented adrenocortical micronodular dysplasia and clinical Cushing's syndrome was investigated. Ascorbate depletion, a process linked to steroid production, was measured by a cyto-chemical bioassay employing guinea pig adrenal explants in organ culture and exposed to IgG from the patients and normal subjects. We also measured cortisol production by these segments during a 5-h culture period using a RIA. For positive reference values we studied the effects of ACTH-(1-39), ACTH-(1-24), ACTH-(11-24), and ACTH-(18-39) on in vitro ascorbate depletion and cortisol production. Both ACTH-(1-39) and ACTH-(1-24) depleted ascorbate and stimulated cortisol production in adrenal cells. The dose-response kinetics of the peptides were bell-shaped; maximal responses were reached in both instances at 1 fmol/L to 10 pmol/L. In all tests, stimulation of in vitro cortisol production was paralleled by ascorbate depletion. ACTH-(18-39) also stimulated ascorbate depletion and cortisol production, but at one concentration only (100 fmol/L), and TSH and LH had no effect. Protein-A-Sepharose-purified IgG preparations of the five patients stimulated ascorbate depletion and/or cortisol production in a dose-dependent fashion; however, the responses occurred over a narrow concentration range (15-150 micrograms IgG/mL culture fluid). These observations support the hypothesis that the hypercortisolism of the syndrome of pigmented adrenocortical micronodular dysplasia is due to circulating Igs that stimulate adrenal steroidogenesis.