Accumulation of amyloid in pituitary adenomas.

The accumulation of amyloid in pituitary adenomas was examined in relation to the types of adenoma and the effect of bromocriptine treatment. Amyloid had accumulated in 34 of 48 adenomas (71%). The occurrence in prolactin-secreting adenomas and growth hormone-secreting adenomas was 79%, respectively, while that in non-functioning adenomas was 50%. Treatment with bromocriptine enhanced the occurrence and extent of the amyloid accumulation in prolactin- or growth hormone-secreting adenomas. Electron microscopy revealed the initial appearance of the amyloid fibrils in the smooth endoplasmic reticulum and a possible sequential process of their release from the cells. The presence of secretory granules in vesicles containing amyloid fibrils and their simultaneous release with amyloid fibrils suggested that degradation of secretory granules was involved in the formation of amyloid.