Ultrastructure of 34 cases of human pituitary adenomas were studied. Ferritin-labeled and horseradish peroxidase-labeled lectin binding sites were also analyzed electronmicroscopically. The 34 cases were divided into three groups; the first was 13 cases of prolactin producing adenomas, the second was 9 cases of human growth hormone (HGH)-producing adenomas and the third group was 12 cases of hormonally non-functioning adenomas. Attention was paid to secretory granules in the adenoma cell and in each group generally admitted features were observed. There were some exceptional cases. Measuring the size of the secretory granules was important not only to differentiate each adenoma cell, but also to detect some unusual cases in each group.
Study of ferritin-labeled lectin binding sites of the adenoma cell plasma membrane revealed significant differences between the prolactin or HGH-producing adenoma group and the hormonally non-functioning group. Ferritinlabeled Ricinus communis agglutinin (which binds to galactose) binding sites were significantly reduced in number in the non-functioning adenoma group when compared to those of HGH or prolactin producing groups.
In the study of horseradish peroxidase (HRP)-labeled lectin binding sites, general features were as follows: 1) HRP-labeled concanavalin A (which binds to mannose) bound to the plasma membrane, nuclear envelope, rough ER and Golgi membrane, and HRP-labeled RCA bound to the plasma membrane and Golgi membrane. 2) The typical secretory granules of the prolactin producing adenoma and HGH-producing adenoma had no lectin binding sites. 3) On the other hand, in an atypical case of HGH-producing adenoma, small secretory granules (mean diameter, 130 nm) had Con A and RCA binding sites in the form of electron dense reaction products. 4) In the non-functioning group, there existed no consistent results concerning the lectin binding sites of the granules (mean diameter, 100-150 nm).
Influence of the trypsinization on the adenoma cell secretory activity was checked by the control study and the result was that the trypsinized adenoma cells had the same secretory activity with the non-trypsinized cells and responded to thyrotropin releasing hormone (0.1 μg/ml).
