Abstract
A 44-year-old man was admitted to the hospital in November 1975 because of an attack of hy poglycemia. The fasting blood glucose, mmunoreactive insulin (IRI) and C-peptide immunoreactivity (CPR) levels were 41-48 mg/dl, 37-71.5 AU/ml and 3.15-5.00 ng/ml, respectively. The blood glucose levels during the hypoglycemic attacks were 19-41 mg/dl. During oral 50 g glucose loading' serum IRI and CPR reached the peak, at 30 min, 496.0 μU/m1 and 12.20 ng/ml, respectively, and intravenous tolbutamide or oral L-leucine administration caused hypoglycemic attack resulting in loss of conciousness and convulsion.
ngiography of the celiac artery revealed the presence of pancreatic tumors, which were resected-Two tumors 1.5×1.25 cm and 1.75×1.0 cm were found at the tail of pancreas. The histological diagnosis was a benign insulinoma.
To investigate the autonomy of insulin secretion from insulinoma, insulin suppression tests were performed administering fish insulin, somatostatin and propranolol-adrenalin, respectively. In the administration of fish insulin, CPR levels, an indicator of endogenous insulin secretion, were not completely suppressed by the induced hypoglycemia. However, somatostatin and propranolol-adrenalin, which have been reported to have a direct suppressive effect on insulin release from the β Cell, suppressed the IRI and CPR.
These results suggest that insulin secretion in this patient was not controlled by blood glucose levels, though it was directly suppressed by somatostatin and propranolol-adrenalin. Therefore, in some cases of insulinoma the suppressive test with exogenously administered insulin may be diagnostically more useful than the stimulatory tests which sometimes have false negative or false positive results.
The serum levels of proinsulin measured by the method or Melani were high before resection of the insulinoma but could not be detected after the operation. The fact indicated that proinsulin was secreted from the insulinoma and that its measurement is important for diagnosing insulinoma.
