Are elevated pancreatic polypeptide levels in patients with insulinoma secondary to hypoglycaemia?

Secretion of pancreatic polypeptide in patients with pancreatic endocrine tumors

Pancreatic polypeptide is often secreted by pancreatic endocrine tumors and is considered a marker for such tumors. To investigate the diagnostic value of this marker, we studied 323 patients with proved pancreatic endocrine tumors. We found plasma concentrations of pancreatic polypeptide to be elevated (more than 300 pmol per liter) in 144 patients (diagnostic sensitivity, 45 percent). However, plasma levels of pancreatic polypeptide can also be elevated in the absence of a pancreatic tumor. To ascertain whether the administration of atropine could distinguish between normal and tumor-associated polypeptide secretion, we studied 30 patients with pancreatic tumors and high plasma levels of pancreatic polypeptide, 18 patients without tumors who had elevated levels of pancreatic polypeptide, and eight normal controls. Polypeptide levels in the 18 patients without tumors were substantially lower than in the 30 patients with tumors. Atropine (1 mg intramuscularly) did not suppress polypeptide levels in patients with tumors, but did suppress plasma levels by more than 50 percent in all subjects without tumors. Thus, although its diagnostic sensitivity is low, pancreatic polypeptide appears to be a useful adjunctive marker of many pancreatic endocrine tumors, and the atropine suppression test can be used to distinguish normal from tumor-related secretion of the polypeptide. Identification of the type of pancreatic endocrine tumor still requires measurement of the hormone that is specific for the tumor.

Can plasma human pancreatic polypeptide be used to detect diseases of the exocrine pancreas?

Plasma concentrations of human pancreatic polypeptide (HPP) parallel exocrine pancreatic secretion in response to stimulation with cholecystokinin. We determined prospectively the relationships among fasting HPP level, integrated HPP response to infusion of cholecystokinin, and output of trypsin and also the sensitivity, specificity, and predictive values of the fasting HPP level in the diagnosis of exocrine pancreatic disease. Our study group consisted of 19 patients with acute pancreatitis, 17 with chronic pancreatitis, and 25 with ductal adenocarcinoma of the pancreas and 27 control subjects. In the control patients and those with chronic pancreatitis, significant correlations were detected between HPP level and output of trypsin (P less than 0.001) in response to infusion of cholecystokinin and between fasting HPP and integrated HPP levels (P less than 0.004); no correlation was detected between HPP level and steatorrhea. The sensitivity, specificity, and negative and positive predictive values of the fasting HPP level for detection of either chronic pancreatitis or pancreatic cancer were similar and approximated 0.88, 0.67, 0.88, and 0.66, respectively. The HPP concentration had no value in detecting acute pancreatitis. Because the fasting HPP level has a high degree of negative predictability and is simpler to measure than the integrated HPP level or the output of trypsin, it may be a useful test in patients suspected of having either chronic pancreatitis or pancreatic cancer. A fasting HPP level of 125 pg/ml or greater could be used to exclude chronic pancreatitis or pancreatic cancer, but the finding of a value of less than 125 pg/ml necessitates use of other diagnostic tests for reliable determination of the presence of these diseases.

Influence of a transplantable insulinoma on the pancreatic status of insulin and pancreatic polypeptide in the rat

The effect of endogenous hyperinsulinaemia, produced by syngeneic transplantation of rat insulinoma at an extrapancreatic site, on pancreatic insulin and pancreatic polypeptide has been examined by radioimmunoassay and immunohistochemistry. Twenty days after subcutaneous transplantation, tumour-bearing rats exhibited marked hyperinsulinaemia and hypoglycaemia, with plasma pancreatic polypeptide concentrations similar to controls. Immunoreactive insulin levels in the head and tail of pancreas of tumour-bearing rats were reduced by 90-95% compared with control animals. Immunoreactive pancreatic polypeptide levels in the head of the pancreas were reduced by 70%, but the relatively low levels of peptide in the pancreatic tail were similar in tumour-bearing and control rats. Insulin and pancreatic polypeptide cells were weakly immunofluorescent in tumour-bearing rat pancreas. In conclusion, the presence of an insulinoma at an extrapancreatic site resulted in a severe depletion of endogenous insulin and pancreatic polypeptide, suggesting that there is a functional relationship between the beta and pancreatic polypeptide cell.

Clinical relevance of regulatory gastrointestinal peptides

The application of radioimmunoassay of insulin, C-peptide, gastrin, glucagon, vasoactive intestinal polypeptides (VIP), somatostatin, human pancreatic polypeptides (hPP), substance P and neurotensin to detect endocrine tumors of the pancreas and other organ systems is undoubtedly important in the clinical management of patients suspected of having tumors that secrete these hormones. Radioimmunoassays of the above gut peptides have certain degrees of specificity and sensitivity; however, there are several factors that need to be considered in the interpretation of results since heterogeneity of molecular forms does occur and the varied radioimmunoassay techniques use different antibodies that may yield different results. It is, therefore, important that each laboratory establish its own normal values, determine the molecular species that each assay is detecting, and also determine the false positivity of the methodology. The same endocrine tumor may contain and secrete several detectable peptides, but the syndrome may relate to only one peptide. Although the simultaneous measurement of multiple peptides in patients with benign gastrointestinal disease has yielded information that contributes to our understanding of the complexities of gut neuroendocrine interaction, the pathophysiological role of gut peptides and their clinical relevance need further evaluation.

Effects of the disaccharidase inhibitor acarbose on meal and intravenous glucose tolerance in normal man

To determine whether the effects of the disaccharidase inhibitor Acarbose on glucose tolerance could be solely explained via an action on intestinal nutrient absorption, the effects of this agent and placebo (100 mg p.o.) on intravenous and postprandial glucose tolerance were compared in six normal subjects. Acarbose significantly diminished plasma glucose, insulin, and gastrointestinal inhibitory polypeptide responses following meal ingestion without affecting plasma glucagon and pancreatic polypeptide responses, but had no effect on plasma glucose and insulin responses following intravenous injection of glucose. These results suggest that the acute effects of Acarbose on glucose tolerance can be explained on the basis of its ability to alter intestinal nutrient absorption.