Multiple forms of gastroenteropancreatic hormones

Decreased expression of neuropeptides in malignant paragangliomas: an immunohistochemical study

Paraffin-embedded sections of 99 human adrenal and extraadrenal paragangliomas were analyzed by the indirect immunoperoxidase technique for the presence of neuron-specific enolase (NSE) and 10 neuropeptides. Each showed diffuse staining for NSE. Most tumors were positive for [Leu5]-enkephalin (76 per cent), [Met5]-enkephalin (75 per cent), somatostatin (67 per cent), and pancreatic polypeptide (51 per cent), followed by vasoactive intestinal polypeptide (VIP) (43 per cent), substance P (31 per cent), ACTH (28 per cent), calcitonin (23 per cent), bombesin (15 per cent), and neurotensin (12 per cent). The neuropeptides paralleled to a large extent those normally found in the sympathetic nervous system. Clinically malignant paragangliomas (n = 25) with proven regional or distant metastases expressed considerably fewer neuropeptides, although the spectrum of those seen remained similar. Malignant paragangliomas contained an average of two neuropeptides per tumor, in contrast to five for the benign tumors (P less than 0.05). Logistic regression analysis of staining results revealed that the paucity of enkephalins, somatostatin, pancreatic polypeptide, and VIP along with the patient's sex was predictive of clinical malignancy. Our results show a definite relationship between expression of neuropeptides and the biologic behavior of these paragangliomas.

Characterization of immunoreactive forms of pancreatic polypeptide in islet cell tumors using antisera with different regional specificities

Tumor tissue from a heterogeneous group of patients with clinically and histologically diagnosed islet cell tumors has been assessed for pancreatic polypeptide (PP) content using radioimmunoassay. Immunoreactive forms of PP, obtained by gel filtration of tissue extracts, were detected using antisera with different regional specificities. Normal pancreatic tissue contained one form of PP coeluting with human PP whereas, tumor tissue from patients with insulinoma, Zollinger-Ellison, and WDHA (watery diarrhea hypokalemic achlorhydric) syndromes contained, in addition, higher molecular weight forms of immunoreactive PP. Furthermore, a lower molecular weight form was detected in tumor tissue from a Zollinger-Ellison syndrome patient. The high molecular weight forms of immunoreactive PP were not recognized using a C-terminal-specific antiserum, whereas the smaller form was only detected using this antiserum. The variation in cross-reactivity observed with two antisera in this study emphasizes the limitations of using a single antiserum to detect molecular forms of peptide hormones, particularly those in islet cell tumors.

Organ and plasma metabolism of neurotensin in sheep

The metabolism of neurotensin (NT) across specific vascular beds of conscious sheep and the stability of NT in plasma have been quantitated. The nature of the metabolites has been characterized with region-specific antiserums and chromatography. NT-(1-13) was infused at 200 pmol X kg-1 X h-1 for 60 min into nine ewes, and blood samples were taken via cannulas in the aorta, pulmonary artery, portal vein, hepatic vein, renal vein, and jugular vein. Two antiserums, one directed towards the N-terminal end of NT (7852) and the other directed to the C-terminal end (C28) were used for radioimmunoassay. Pancreatic polypeptide (PP) was measured also. Using the steady-state concentrations in the aorta, the metabolic clearance rate of NT measured with C28 was 25.8 +/- 3.2 ml X kg-1 X min-1, twice that with 7852. The kidney, brain, and gut were the major organs clearing NT with a greater disappearance of C-terminal than N-terminal immunoreactivity. Gel chromatography of plasma at steady state showed that the NT immunoreactivity consisted of intact NT and N-terminal fragments; no C-terminal fragments were detected. Similarly, incubation of NT in plasma in vitro resulted in the generation of stable N-terminal fragments. The kidney was also the major organ involved in the clearance of PP both in the basal state and after stimulation by NT. Because the C-terminal end of NT is biologically active, these studies suggest that either N-terminal fragments have some unknown biological role or that NT is acting as a local hormone.

Neuropeptide Y in phaeochromocytomas and ganglioneuroblastomas

Tumour tissue from nineteen patients with phaeochromocytomas and nine with ganglioneuroblastomas contained large numbers of neuropeptide Y (NPY) producing cells and extracts of these tumours had very high concentrations of immunoreactive NPY. Plasma NPY concentrations were also raised, averaging 460 pmol/l in patients with tumours of the sympathetic chain and 55 pmol/l in healthy controls. Since plasma NPY is straightforward to measure and relatively stable, its estimation may prove helpful as a screening tests for phaeochromocytoma.