Bilateral macronodular adrenal hyperplasia is a rare cause of primary adrenal Cushing's syndrome. In this form of hyperplasia, hypersecretion of cortisol suppresses the release of corticotropin by pituitary corticotrophs, which results in low plasma corticotropin levels. Thus, the disease has been termed corticotropin-independent macronodular adrenal hyperplasia.
Researchers have examined the abnormal production of corticotropin in these hyperplastic adrenal glands.
Specimens of hyperplastic macronodular adrenal tissue from 30 patients with primary adrenal disease were obtained. The corticotropin precursor proopiomelanocortin and corticotropin expression were assessed by means of a polymerase-chain-reaction assay and immunohistochemical analysis.
The production of corticotropin and cortisol was assessed in 11 specimens with the use of incubated explants and cell cultures coupled with hormone assays.
Corticotropin levels were measured in adrenal and peripheral venous blood samples from 2 patients.
The expression of proopiomelanocortin messenger RNA ( POMC mRNA ) was detected in all samples of hyperplastic adrenal tissue. Corticotropin was detected in steroidogenic cells arranged in clusters that were disseminated throughout the adrenal specimens.
Adrenal corticotropin levels were higher in adrenal venous blood samples than in peripheral venous samples, a finding that was consistent with local production of the peptide within the hyperplastic adrenals.
The release of adrenal corticotropin was stimulated by ligands of aberrant membrane receptors but not by corticotropin-releasing hormone or Dexamethasone.
A semiquantitative score for corticotropin immunostaining in the samples correlated with basal plasma cortisol levels.
Corticotropin-receptor antagonists significantly inhibited in vitro cortisol secretion.
The study has revealed that cortisol secretion by the adrenals in patients with macronodular hyperplasia and Cushing's syndrome appears to be regulated by corticotropin, which is produced by a subpopulation of steroidogenic cells in the hyperplastic adrenals. Thus, the hypercortisolism associated with bilateral macronodular adrenal hyperplasia appears to be corticotropin-dependent. ( Xagena )
Louiset E et al, N Engl J Med 2013; 369:2115-2125