Hans Mårtensson

Improved glucose tolerance and insulin secretion by inhibition of dipeptidyl peptidase IV in mice

We explored whether inhibition of the enzyme dipeptidyl peptidase IV (DPP IV) increases endogenous levels of glucagon-like peptide-1 (GLP-1) and improves glucose tolerance and insulin secretion in mice. Glucose (150 mg) was administered through a gastric gavage with or without the inhibitor of dipeptidyl peptidase IV, valine-pyrrolidide (100 micromol/kg), in high-fat fed glucose intolerant or control C57BL/6J mice. The increase in plasma GLP-1 after gastric glucose was potentiated by dipeptidyl peptidase IV inhibition (P<0.05). Valine-pyrrolidide also potentiated the plasma insulin response to gastric glucose and improved the glucose tolerance in both groups of mice (P<0.001). In contrast, valine-pyrrolidide did not affect glucose-stimulated insulin secretion from isolated islets. This suggests that valine-pyrrolidide improves insulin secretion and glucose tolerance through indirect action, probably through augmentation of levels of GLP-1 and other incretin hormones. Therefore, inhibition of dipeptidyl peptidase IV activity is feasible to exploit as a treatment for glucose intolerance and type 2 diabetes.

Immunohistochemical evidence of peptide hormones in endocrine tumors of the rectum

Twenty‐five endocrine tumors of the rectum (rectal carcinoids) were examined immunohistochemically for various pancreatic and gut neurohormonal polypeptides. Twenty‐one of the tumors were found to contain cells displaying pancreatic polypeptide (PP), glucagon, somatostatin, insulin, substance P, enkephalin or β‐endorphin immunoreactivity. At least 11 of the tumors contained more than one peptide hormone. In some of the tumors PP cells made up the major cell population, in others the glucagon cells constituted the majority. Only four of the tumors contained 5‐hydroxytryptamine. Rectal endocrine tumors seem unique among gut endocrine tumors in that they may store immunoreactive enkephalin, β‐endorphin and even insulin. None of the patients displayed the carcinoid syndrome; symptoms were usually vague and uncharacteristic. In many cases the tumor was found at routine examination.

Elevated concentrations of substance p and 5-HT in plasma in patients with carcinoid tumors

Ten patients with metastatic carcinoid tumors in the liver showed elevated 5‐hydroxytryptamine and substance P levels in plasma samples taken from hepatic or peripheral veins. Chromatographic characterization of the substance P‐immunoreactivity showed that by gel permeation and high pressure liquid chromatography the substance P‐immunoreactivity was indistinguishable from synthetic undecapeptide substance P. The results suggest that substance P, in addition to the 5‐hydroxyinoles, may serve as a circulatory marker for some forms of carcinoid tumors.

Effects of calcitonin gene-related peptide (CGRP) on islet hormone secretion in the pig

SummaryCalcitonin gene-related peptide occurs in intrapancreatic nerves and endocrine cells. The peptide is therefore a candidate for being of physiological importance for pancreatic function. We examined the direct effects of calcitonin gene-related peptide on islet hormone secretion in the pig by infusing the peptide into the superior pancreatic artery. We found that 15 min intrapancreatic infusion of calcitonin gene-related peptide (22 pmol/min) decreased baseline pancreatic insulin output from 48±10 μU/min to 8±7μU/min (p<0.01). Moreover, calcitonin gene-related peptide inhibited glucose-induced insulin secretion by 45% compared to controls (p<0.01), yet left terbutaline (β2-adrenoceptor)-stimulated insulin secretion unaffected. Furthermore, while being without effect on baseline glucagon output, calcitonin gene-related peptide potentiated terbutaline-induced glucagon secretion more than seven-fold (p<0.001). In contrast, the peptide did not affect baseline or stimulated pancreatic somatostatin output. We conclude that in pigs calcitonin gene-related peptide inhibits insulin secretion and potentiates glucagon secretion by direct effects on the pancreas that are not mediated by primary alterations in pancreatic somatostatin secretion. We suggest that the neuropeptide calcitonin gene-related peptide might be of importance for the intrapancreatic regulation of insulin and glucagon secretion in pigs.

Neurohormonal Peptides in Endocrine Tumors of the Pancreas, Stomach, and Upper Small Intestine: I. An Immunohistochemical Study of 27 Cases

Preliminary observations have indicated the existence of characteristic spectra of gastroenteropancreatic (GEP) neurohormonal peptides in endocrine tumors arising in foregut, midgut, and hindgut derivatives. In order to further explore this feature of GEP endocrine neoplasms, islet cell tumors from 14 patients were studied, as were endocrine tumors of the stomach, duodenum, and upper jejunum from 6, 5, and 2 patients, respectively. All tumors were examined immunohistochemically with antisera raised against islet hormones [insulin, somatostatin, glucagon, pancreatic polypeptide (PP)], peptides of the gastrin family [gastrin, cholecystokinin (CCK)], peptides of the secretin family [secretin, vasoactive intestinal peptide (VIP)], and substance P, neurotensin, leu-enkephalin, beta-endorphin, motilin, calcitonin, and ACTH. In addition, an ultrastructural investigation was made. Whenever possible, the immunohistochemical observations were correlated with the clinical manifestations and with the results of radioimmunochemical determination of GEP neurohormones in the blood. The pattern of immunoreactive neurohormonal peptides and the clinical picture were those to be expected in endocrine tumors arising in foregut derivatives. Some principles are proposed for the classification of GEP endocrine tumors on the basis of their histopathologic growth pattern, their spectrum of neurohormonal peptides, and their clinical manifestations.

Endocrine tumors of the ileum. Cytochemical and clinical aspects.

Sixteen patients with endocrine ileal tumors and liver metastases were analyzed with regard to the size, multicentricity, and growth pattern of the primary tumor, the occurrence of carcinoid syndrome, as well as the concentrations of serotonin and substance P (SP) in blood, 5-hydroxy-indole-acetic acid (5-HIAA) in urine, and the course of the disease. Excised specimens from the tumors were immediately processed for immunocytochemical investigations of the presence of neurohormonal peptides, using a broad spectrum of antisera and optimal histoprocessing techniques. In all patients the serotonin levels in blood and/or the 5-HIAA in urine were high. The SP concentration in plasma was markedly elevated in all but two of the ten patients investigated in this respect. A mixed growth pattern prevailed in the tumors of 7 patients with fatal disease. Serotonin cells were found in all tumors and SP-immunoreactive tumor cells in all but one; one of the carcinoids also contained a few tumor cells displaying enkephalin immunoreactivity. In conventionally fixed and paraffin embedded specimens of the same tumors usually no immunoreactive tumor cells at all could be demonstrated, showing that SP is among the peptides vulnerable to poor histotechniques. Nevertheless, SP, together with serotonin, constitute reliable clinical tumor markers for ileal carcinoids.

Cholecystokinin (CCK)-4 and CCK-8 stimulate islet hormone secretion in vivo in the pig.

It is known that cholecystokinin (CCK) stimulates islet hormone secretion under a variety of experimental conditions. Since CCK occurs in several different molecular forms, with 58, 39, 33, 12, 8, or 4 amino acid residues, the question has evolved as to which is the shortest active form of CCK. We therefore investigated the influences of the C-terminal octapeptide of CCK, CCK-8 (sulfated form) and of the C-terminal tetrapeptide, CCK-4, on the secretion of insulin, glucagon, and somatostatin from the pig pancreas in vivo by infusing each of the two peptides into the superior pancreatic artery. We found that islet hormone secretion increased promptly upon infusion of both CCK-8 and CCK-4. Thus, the secretion of insulin was stimulated from 51 ± 12 to 295 ± 70 μU/min during the first 2 min after injection of CCK-8 and from 40 ± 12 to 240 ± 78 μU/min after injection of CCK-4. Similarly, the secretion of glucagon was stimulated from 240 ± 45 to 357 ± 38 μg/min after CCK-8 and from 282 ± 44 to 335 ± 43 μg/min after CCK-4, and somatostatin secretion was stimulated from 112 ± 7 to 226 ± 12 μg/min by CCK-8 and from 105 ± 11 to 246 ± 16 pg/min by CCK-4. With regard to the efficiency to stimulate the secretion of these three islet hormones, CCK-8 and CCK-4 were equipotent. We conclude that in pigs, CCK-8 and CCK-4 both stimulate the secretion of insulin, glucagon, and somatostatin from the pancreas in vivo. Hence, the active site in the CCK molecule to stimulate islet hormone secretion in pigs seems to reside in the C-terminal tetrapeptide residue.

Localization and peptide content of endocrine pancreatic tumors.

Endocrine pancreatic tumors contain and frequently secret neurohormonal peptides. This phenomenon can be used as a diagnostic and classifying tool. This study analyzes 31 patients operated on because of an endocrine pancreatic tumor, including the diagnostic procedures and the localization methods. In 15 insulinoma cases only 6 patients had a positive arteriography, while all 11 selective pancreatic vein samplings were positive. The immunoreactivity showed that, besides insulin, most tumors also contained other peptides. Of four gastrinoma cases the arteriography was positive in three, but the selective vein sampling localized the tumor in all. The tumors content of peptides showed mixed patterns. In the four glucagonomas, the arteriography was positive in all and the venous sampling performed in three of the cases also was positive. In five pancreatic polypeptide-containing tumors (PP-omas) the arteriography was positive in four and sampling performed in two was positive in both. In the PP-omas the peptide pattern showed that these tumors frequently contain several peptides. We used selective pancreatic vein sampling in 21 cases with positive result in all. In the cases in which arteriography was negative, the sampling results helped the surgeon to find the tumor. The peptide pattern in the tumors varied greatly and most tumors were multihormonal.

Pancreatic nerve stimulation releases neuropeptide Y- but not galanin- or calcitonin gene-related peptide-like immunoreactivity from the pig pancreas

We investigated the possible release of galanin-, calcitonin gene-related peptide (CGRP)-, and neuropeptide Y (NPY)-like immunoreactivity from the pancreatic nerves in thiopental-anaesthetized pigs. Ten minutes stimulation of the mixed autonomic pancreatic nerves during infusion of atropine (8 or 40 Hz, 5 ms, 10 mA, n = 5) inhibited insulin secretion, during both normoglycemia (9.1 +/- 0.2 mmol/l) and hyperglycemia (28.1 +/- 0.4 mmol/l). Concomitantly, pancreatic venous concentrations of NPY-like immunoreactivity increased. For example during normoglycemia, a nerve stimulation by 8 Hz increased the pancreatic venous levels of NPY-like immunoreactivity from 294 +/- 26 pmol/l to 391 +/- 23 pmol/l (P less than 0.001). In contrast, the pancreatic venous concentrations of galanin- or CGRP-like immunoreactivity did not change during the nerve stimulation. We conclude that electrical pancreatic nerve stimulation in the pig releases NPY-like immunoreactivity without affecting the pancreatic venous concentrations of galanin- or CGRP-like immunoreactivity.

Pancreatic release of pancreastatin in the pig

It is known that pancreastatin-like immunoreactivity (PLI) occurs in the secretory granules of the islet B- and D-cells in the pig pancreas, and that porcine pancreastatin inhibits insulin secretion in rats and mice. In this study, we characterized the porcine plasma PLI and examined whether PLI is released from the pig pancreas in vivo. We found that PLI in unextracted pig plasma largely consists of two high-molecular fractions, with Mr values of 80–85,000 and 300–350,000, respectively. In addition, a small peak of PLI eluted after gel filtration at the position of synthetic porcine pancreastatin. After extraction on octadecylsilyl silica, virtually all PLI disappeared except in the fraction co-eluting with porcine pancreastatin. In thiopenthal-anesthetized pigs, plasma samples were obtained from the carotid artery and the superior pancreaticoduodenal vein. By multiplying the venous-arterial concentration difference by the pancreatic venous plasma flow, a net pancreatic output of PLI of 420 ± 120 pmol/min was found. This pancreatic PLI output was significantly reduced by electrical stimulation of the local autonomic nerves along the superior artery during atropine administration (p < 0.001). Furthermore, the pancreatic venous PLI levels were elevated during intravenous infusion of glucose (p < 0.01). We conclude that pig plasma PLI levels can be measured by radioimmunoassay after extraction on octadecylsilyl silica and that there is a net pancreatic output of PLI, which is reduced by sympathetic stimulation and enhanced during hyperglycemia.