Plasma
somatostatin immunoreactivity (SIR) was elevated 40-fold in an
insulin-treated diabetic with disseminated
pancreatic carcinoma. The diagnosis of
somatostatinoma was supported by histological and ultrastructural similarities between metastatic cells and pancreatic D cells. Under
acid conditions, 75% of the plasma SIR eluted as a 6000- to 7000-dalton
protein and 25% as synthetic
somatostatin (mol wt 1600), whereas the 20-fold elevated urine SIR consisted almost exclusively of the higher molecular weight fraction. The hypersomatostatinemia was associated with reduced basal and stimulated pancreatic
hormone levels, which might reflect its involvement in the
steatorrhea and diabetes, and its protection against
ketoacidosis. Plasma SIR rose 50% upon
insulin withdrawal and 10-fold after
tolbutamide injection and fell 30% after
diazoxide. It is concluded that an increase in plasma and urine SIR, the presence of a 6000- to 7000-dalton SIR fraction in plasma and urine, a reduction in basal and stimulated pancreatic
hormone levels, and
tolbutamide-induced
somatostatin release can be diagnostic for a
somatostatinoma.
Streptozotocin reduced
tumor volume, hypersomatostatinemia, and
tolbutamide-induced
somatostatin release, suggesting that this
drug may be useful in the treatment of disseminated
somatostatinoma.