Inhibins and activins are dimeric proteins of the transforming growth factor-beta superfamily which have been shown to be expressed in the adrenal cortex. Recent studies have suggested a role for these peptides in the pathogenesis and/or function of adrenal tumours. To investigate further their physiological and pathological roles, we have documented immunoreactivity for inhibin alpha, betaA and betaB subunits in normal adult and fetal human adrenals, in hyperplastic adrenals and in adrenal tumours. In the normal and hyperplastic adult gland, diffuse immunopositivity was demonstrated for beta subunits, suggesting that activins (beta beta dimers) can be expressed in all zones. Inhibin alpha was limited to the zona reticularis and the innermost zona fasciculata in the normal gland, extending centripetally into the zona fasciculata in hyperplasia, supporting a role for ACTH in the regulation of expression, and suggesting that expression of inhibins (alpha beta dimers) is restricted. Immunopositivity for all three subunits was seen in both fetal and definitive zones of the fetal cortex, indicating that both inhibins and activins could be expressed in both. Immunopositivity for all three subunits was seen in most adrenocortical tumours. Loss of immunopositivity for inhibin alpha in a subgroup of carcinomas might indicate a role in tumour progression. The greater intensity of staining for inhibin alpha in tumours associated with Cushing's syndrome again suggests a link with cortisol production.

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