Morphometric analysis of secretory granules and prolactin levels in chromophobe pituitary adenoma

Morphometric analysis of secretory granules was performed in 16 chromophobe adenomas: seven undifferentiated cell adenomas (group A), two of which were accompanied by mild hyperprolactinemia and nine prolactin cell sparsely granulated adenomas (group B), all associated with hyperprolactinemia. The results of morphometry were correlated with levels of prolactin in tumor and serum. The range of granule diameters was similar in both groups but granule size frequency was different resulting in a characteristic histogram for each group. Poor relationship existed between granule mean diameter and prolactin in tissue of the group B. In the same group there was virtually no linear relationship between serum prolactin on one side and granule mean diameter, granule density or tissue prolactin on the other. Also in the group B a paradoxical inverse relationship was found between granule density and tumor prolactin. Apparently, in prolactin cell adenoma a sizable part of hormone is located outside of mature secretory granules. An abundance of immature granules, misplaced exocytosis, crinophagia or defect in packaging of the hormone could all explain this paradox but the last possibility seems most plausible.