Adrenal mast cells can stimulate aldosterone secretion through the local release of serotonin (5-HT) and activation of the 5-HT₄ receptor (5-HT₄). In aldosterone-producing adenomas (APAs), 5-HT₄ receptor is overexpressed and the administration of 5-HT₄ receptor agonists to patients with APA increases plasma aldosterone levels. These data and the well-documented role of mast cells in tumorigenesis suggest that mast cells may be involved in the pathophysiology of APA.

The study aimed at investigating the occurrence of mast cells in a series of APA tissues and to examine the influence of mast cells on aldosterone secretion.

The occurrence of mast cells in APAs was investigated by immunohistochemistry. Mast cell densities were compared with clinical data. The influence of mast cells on aldosterone production was studied by using cultures of human mast cell and adrenocortical cell lines.

In APA tissues, the density of mast cells was found to be increased in comparison with normal adrenals. Mast cells were primarily observed in adrenal cortex adjacent to adenomas or in the adenomas themselves, distinguishing two groups of APAs. A subset of adenomas was found to contain a high density of intratumoral mast cells, which was correlated with aldosterone synthase expression and in vivo aldosterone secretory parameters. Administration of conditioned medium from cultures of human mast cell lines to human adrenocortical cells induced a significant increase in aldosterone synthase (CYP11B2) mRNA expression and aldosterone production.

APA tissues commonly contain numerous mast cells that may influence aldosterone secretion through the local release of regulatory factors.