Basement membrane proteins and apolipoprotein E in growth hormone secreting adenomas and their correlation to amyloid: an immunoelectron microscopic study.

Having previously demonstrated the association of basement membrane components (BMC), as well as apolipoprotein E and amyloid in growth hormone (GH)-producing pituitary adenomas, the aim of this study was to further analyze this relationship at the ultrastructural level. Ultrathin sections from four amyloidotic sparsely granulated monohormonal GH-producing adenomas previously investigated light microscopically were selected. Immunoelectron microscopy was performed, using a single labeling postembedding on-grid Protein-A gold method with antisera directed against laminin, fibronectin and apolipoprotein E. In all four adenomas, anti-laminin, anti-fibronectin, and anti-apolipoprotein E reacted with amyloid fibrils. No BMC were demonstrated between amyloid deposits, making it likely that synthesis and deposition of BMC may be secondary to the deposition of amyloid. The intimate spatial relationship between BMC as well as apolipoprotein E and amyloid fibrils may indicate morphological evidence of a particular arrangement of amyloid components in GH-secreting adenoma amyloid and a pathophysiological link.