Effect of growth hormone on high plasma levels of glucagon-like peptide-1 (GLP-1) in hypophysectomized rats.

Fasting plasma GLP-1 levels were significantly higher in hypophysectomized (hypox) rats (n = 6) than in intact (normal) rats (n = 7) (54.3 +/- 5.2 vs. 33.3 +/- 2.4 pmol/L, p < 0.001). To examine the influence of pituitary hormones on plasma GLP-1 levels, concentrations of plasma glucose, insulin and GLP-1 after an oral glucose load to hypox rats that were given either rat growth hormone (rGH) (n = 7), cortisol and thyroxine (n = 7) or no substitution (n = 6) were compared with those of normal rats (n = 7). Plasma glucose levels in the fasting state and after the glucose ingestion were significantly lower in hypox rats, but the hormonal replacements to hypox rats increased their total glucose levels to those of normal rats, although the increasing patterns were different from those in normal rats. Insulin levels both in the fasting state and after the glucose ingestion were significantly decreased in hypox rats and the fasting and total GLP-1 levels were significantly increased in those rats. rGH substitution significantly increased the total insulin levels in hypox rats and decreased the fasting and total GLP-1 levels closely to levels in normal rats, while substitution with cortisol and thyroxine failed to introduce such a significant effect. These results suggested that secretion of GLP-1 might be influenced by the function of GH.

Measurements of both hippocampal blood flow and hippocampal gray matter volume in the same individuals with Alzheimer's disease.

We evaluated both hippocampal blood flow and hippocampal gray matter volume using single photon emission tomography and magnetic resonance imaging in the same individuals with Alzheimer's disease (AD) and in age-matched controls. The hippocampal blood flow was not significantly lower in mild AD patients (n = 21, Mini-Mental State Examination (MMSE) 23.3+/-2.1) than in controls (n = 16) with a 57% overlap. The hippocampal blood flow was significantly lower in advanced AD patients (n = 22, MMSE 15.4+/-3.2) than in controls. The hippocampal gray matter volume was significantly smaller in mild AD patients than in controls, although a 43% overlap was present. There was no significant difference in the hippocampal gray matter volume between the mild and advanced AD patients. The combination of measurements of hippocampal blood flow and gray matter volume discriminated 71% of mild AD patients from controls. These results suggest the usefulness of a combined analysis of hippocampal blood flow and gray matter volume for the early diagnosis of AD.

Disaccharide analysis of chondroitin sulfate in peri-implant sulcus fluid from dental implants.

We collected peri-implant sulcus fluid by capillary tubes from sites around titanium osseointegrated implants and determined the chondroitin sulfate released into the peri-implant sulcus fluid by high-performance liquid chromatography. Chondroitin sulfate was found in all peri-implant sulcus fluid samples, and its content was similar to that in gingival crevicular fluid obtained around natural teeth. The predominant unsaturated disaccharide isomer was delta Di-0S, followed by delta Di-4S. Delta Di-6S was present in trace amounts. The amount of delta Di-0S was greater in peri-implant sulcus fluid than in gingival crevicular fluid. Assaying chondroitin sulfate disaccharides in peri-implant sulcus fluid may be an effective method of monitoring the peri-implant condition of dental implants.

Comparison of chromogranin A and pancreastatin levels in plasma of patients with pancreatic islet cell tumor.

The plasma levels of chromogranin A (CGA) in patients with islet cell tumor and plasma CGA responses to administration of a somatostatin analogue (Octreotide) in two of these patients were examined in comparison with plasma pancreastatin (PST) levels. There was a significant correlation between the fasting plasma levels of CGA and PST (r = 0.6, P < 0.001). Administration of the somatostatin analogue reduced the plasma concentrations of PST and CGA within 1 h, but the responses of CGA and PST to the analogue were not parallel in either patient. Thus, the suppressive effects of the analogue on the secretions of PST and CGA may be different. The results suggest the value of the PST and CGA assays used in this study.

Production and secretion of chromogranin A and pancreastatin by the human pancreatic carcinoma cell line QGP-1N on stimulation with carbachol.

Chromogranin A (CGA) is thought to be a precursor of pancreastatin (PST). Carbachol (Cch) stimulated the secretion of CGA and PST from QGP-1N cells derived from a human pancreatic islet cell tumor. Atropine inhibited the secretion of both. Sodium fluoride, phorbol ester, and calcium ionophore also stimulated the secretion of both. Cch (10(-5) M) stimulated inositol 1,4,5-trisphosphate production in QGP-1N cells. Stimulation with Cch increased the total amount of PST in the cells and the medium 1.7-fold and decreased the amount of CGA in the cells and medium. QGP-1N cells were labelled with [35S]methionine, and then CGA and PST in the cells and medium were immunoprecipitated with specific antisera, and separated by electrophoresis in polyacrylamide gel. Stimulation with Cch resulted in an increase in the intensity of PST-immunoreactive bands and a decrease in those of CGA-immunoreactive bands. Cch did not increase the cellular level of CGA messenger RNA. These results suggested that (1) the secretion of CGA and PST from QGP-1N cells is regulated mainly through muscarinic receptors coupled with activation of polyphosphoinositide breakdown by a G protein, with intracellular calcium ion and protein kinase C playing a role in the stimulus-secretion coupling and that (2) Cch may induce the secretion of PST and CGA and processing from CGA to PST.

Pancreastatin molecular forms in normal human plasma.

Circulating molecular forms with pancreastatin (PST)-like immunoreactivity in plasma from normal subjects were examined. An immunoreactive form corresponding to a human PST-like sequence [human chromogranin-A-(250-301)] (hPST-52) and a larger form (mol wt 15-21 kDa) were detected by gel filtration of plasma from normal subjects. On high performance liquid chromatography, predominant immunoreactive forms coeluted with the three larger forms which were purified from the xenograft of human pancreatic islet cell carcinoma cell line QGP-1N cells and with synthetic hPST-52. The fraction containing larger forms purified from xenograft of QGP-1N cells had biological activity equivalent to that of hPST-52 on the inhibition of pancreatic exocrine secretion. These results suggest that the larger molecular forms as well as hPST-52 may be physiologically important circulating forms of PST in human.

Secretion of neurotensin from a human pancreatic islet cell carcinoma cell line (QGP-1N).

Effects of various secretagogues on secretion of neurotensin from a pancreatic islet cell carcinoma cell line (QGP-1N) were examined. Carbachol stimulated secretion of neurotensin concentration-dependently in the range of 10(-6) - 10(-4) M. The neurotensin secretion stimulated with 10(-5) M carbachol was completely inhibited by atropine at 10(-5) M. Phorbol ester and calcium ionophore (A23187) stimulated secretion of neurotensin. The removal of extracellular Ca2+ suppressed the secretion through the stimulation with 10(-5) M carbachol. Fluoride, an activator of guanine nucleotide-binding (G) protein, stimulated secretion of neurotensin. Neurotensin released into culture medium through stimulation with carbachol coeluted with neurotensin 1-13 on a gel-chromatography. Our results suggest that secretion of neurotensin from QGP-1N cells is mainly regulated by acetylcholine through muscarinic receptors coupled to G protein and that an increase in intracellular Ca2+ and protein kinase C play an important role in stimulus-secretion coupling.

Parallel secretion of pancreastatin and somatostatin from human pancreastatin producing cell line (QGP-1N).

In this investigation we studied pancreastatin (PST) secretion from a human PST producing cell line (QGP-1N) in response to various secretagogues. Immunocytochemical study revealed the immunoreactivity of PST and somatostatin (SMT) in the same cells of a monolayer culture. Ki-ras DNA point mutation on codon 12 was found. Carbachol stimulated secretion of PST and SMT and intracellular Ca2+ mobilization in the range of 10(-6)-10(-4) M. The secretion and Ca2+ mobilization were inhibited by atropine, a muscarinic receptor antagonist. Phorbol ester and calcium ionophore (A23187) stimulated secretion of PST and SMT. The removal of extracellular calcium suppressed both secretions throughout stimulation with 10(-5) M carbachol. Fluoride, a well-known activator of guanine nucleotide binding (G) protein, stimulated intracellular Ca2+ mobilization and secretion of PST and SMT in a dose-dependent manner in the range of 5-40 mM. Also, 10(-5) M carbachol and 20 mM fluoride stimulated inositol 1,4,5-triphosphate production. However, cholecystokinin and gastrin-releasing peptide did not stimulate Ca2+ mobilization or secretion of the two peptides. These results suggest that secretion of PST and SMT from QGP-1N cells is regulated mainly by acetylcholine in a parallel fashion through muscarinic receptors coupled to the activation of polyphosphoinositide breakdown by a G-protein and that increases in intracellular Ca2+ and protein kinase C play an important role in stimulus-secretion coupling.

Interaction between phosphoinositide turnover system and cyclic AMP pathway for the secretion of pancreastatin and somatostatin from QGP-1N cells.

It is found that secretion of pancreastatin and somatostatin from QGP-1N cells is regulated through muscarinic receptor-mediated activation of phosphatidylinositide hydrolysis system. In this report, whether the cAMP pathway interacts with the phosphoinositide turnover system for the secretion of pancreastatin and somatostatin from QGP-1N cells through muscarinic receptors was studied. Stimulation of QGP-1N cells with carbachol increased intracellular cAMP levels. The carbachol-induced increase in cAMP levels was inhibited by atropine. Calcium ionophore (A23187) and phorbol 12-myristate 13-acetate increased cAMP synthesis. Dibutyryl cAMP, forskolin and theophylline stimulated secretion of pancreastatin and somatostatin. When either dibutyryl cAMP, forskolin or theophylline was added in culture medium with A23187, phorbol ester or carbachol, a synergistic effect was found on pancreastatin and somatostatin secretion. These results suggest that interaction between the phosphoinositide turnover system and the cAMP pathway occurs in QGP-1N cells through muscarinic receptor stimulation for the secretion of pancreastatin and somatostatin.

Degradation of human pancreastatin-52 by human kidney extract.

We examined the in vitro degradation of human pancreastatin-52 (hPST-52) and a larger molecular form (approximate 15 kDa) of human PST by an enzyme extract from human kidney. The PST-degrading activity was determined from the amount of immunoreactive PST remaining after incubation of hPST-52 or the larger molecular form with the enzyme extract. Human PST-52 was degraded to smaller molecular forms within 30 min, but the larger molecule was not degraded within 90 min. Phosphoramidon, an inhibitor of endopeptidase, metal ion chelators (EDTA and 1, 10-phenanthroline) and Cu2+ prevented the degradation of hPST-52. These results indicated that the enzyme in the kidney extract degraded hPST-52 and smaller forms of the peptide, but had no effect on the 15 kDa form.