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Biomedical subjects

D Grandt

Publications and source records attributed to D Grandt.

At least 37 records · Page 2Linked to original sources
PubMed1995

Ileal release of glucagon-like peptide-1 (GLP-1). Association with inhibition of gastric acid secretion in humans.

There is evidence that the distal intestine participates in the regulation of gastric motor and secretory function. It was the aim of this study to examine in greater detail the effects of ileal nutrient exposure on human gastric acid secretion and to investigate potential intermediary mechanisms. Twelve normal subjects were intubated with an oroileal multilumen tube assembly for gastric, duodenal, and ileal perfusion of marker and test solutions, aspiration, and intestinal manometry. We studied ileal effects on gastric acid output in the unstimulated, interdigestive state (during early phase II, N = 6), and during endogenous stimulation by intraduodenal essential amino acid perfusion, N = 6) and on release of candidate humoral mediators, peptide YY (PYY) and glucagonlike peptide-1 (GLP-1), both known inhibitors of human gastric acid secretion. Compared with ileal saline perfusion, ileal carbohydrate (total caloric load: 60 kcal) decreased interdigestive gastric acid output by 64% (P < 0.01), and endogenously stimulated output by 68%, respectively (P < 0.005). Under all experimental conditions, ileal carbohydrate increased plasma GLP-1 by 80-100% (all P < 0.005). Ileal lipid perfusion had similar inhibitory effects on gastric acid output and stimulatory effects on GLP-1 release as had ileal carbohydrate. By contrast, ileal perfusion with peptone had no or only weak effects on either acid output or plasma GLP-1. Plasma PYY concentrations and suppression of gastric secretion in response to ileal perfusions were not correlated. In humans, both interdigestive and endogenously stimulated gastric acid output are inhibited in response to intraileal carbohydrate or lipids, but not protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Peptide YY inhibits exocrine pancreatic secretion in isolated perfused rat pancreas by Y1 receptors.

Peptide YY (PYY) inhibits exocrine pancreatic secretion in several species. Two receptors, Y1 and Y2, are known to mediate PYY actions. While PYY 1-36 binds equally to both receptor subtypes, a second endogenous form of PYY, PYY 3-36, selectively activates Y2 receptors. The importance of Y receptor subtypes for inhibition of exocrine pancreatic secretion by PYY is unknown. We studied the effects of PYY 1-36 on cholecystokinin octapeptide (CCK-8)-stimulated amylase secretion in an isolated perfused rat pancreas model. To characterize functionally the receptors involved we determined the effects of a Y1-selective agonist, [Pro34]PYY; a Y2 selective agonist, PYY 3-36; and neuropeptide Y (NPY) in this model. PYY 1-36 significantly inhibited stimulated amylase secretion in the denervated rat pancreas. [Pro34]PYY and NPY both inhibited exocrine pancreatic secretion as potently as PYY 1-36. Contrary to that, the Y2 selective agonist, PYY 3-36, was inactive. We conclude that PYY inhibits exocrine pancreatic secretion in this extrinsically denervated rat pancreas model by Y1 receptors.

Amylases↗
PubMed1994

[Pro34]peptide YY is a Y1-selective agonist at peptide YY/neuropeptide Y receptors.

We have investigated binding and functional effects of a new peptide YY analogue, [Pro34]peptide YY, at Y1 and Y2-like subtypes of receptors for peptide YY and neuropeptide Y. In binding studies [Pro34]peptide YY had a similarly high affinity as peptide YY to human Y1-like receptors in SK-N-MC cells, a human neuroblastoma cell line of presumed neurogenic origin, and HEL cells, a human cell line derived from a patient with Hodgkin's disease. In functional studies [Pro34]peptide YY stimulated Ca2+ elevations in both Y1-like receptor cell lines with similar potency and efficacy as peptide YY. In contrast to peptide YY [Pro34]peptide YY was 1000-fold less potent in binding to Y2-like receptors in porcine splenic membranes and lacked agonistic effects in another Y2-like receptor-mediated model system, i.e. inhibition of [3H]serotonin release from rat cerebral cortical slices. Thus, [Pro34]peptide YY is a highly Y1-selective full agonist of peptide YY/neuropeptide Y receptors. [Pro34]peptide YY could be useful for studying the importance of Y receptor subtypes in mediating peptide YY physiological actions.

Amino Acid Sequence↗
PubMed1994

Two molecular forms of peptide YY (PYY) are abundant in human blood: characterization of a radioimmunoassay recognizing PYY 1-36 and PYY 3-36.

Two endogenous forms of PYY are abundant in man and dog, PYY 1-36 (PYY-I) and PYY 3-36 (PYY-II). PYY-II is a major molecular form of PYY in human colon, but it is not known, whether PYY-II is also released into the circulating blood. Several radioimmunoassays for measuring PYY-I in plasma have been developed, but it has not been reported, whether they equally detect PYY-II. We characterize a radioimmunoassay for measuring PYY in human plasma which equally recognizes PYY-I and PYY-II. Using this radioimmunoassay and reversed phase HPLC we demonstrate the existence of two forms of PYY in human blood, coeluting with synthetic PYY-I and PYY-II.

Adult↗
PubMed1994

Characterization of two forms of peptide YY, PYY(1-36) and PYY(3-36), in the rabbit.

Peptide YY (PYY) has been purified as a 36 amino acid peptide from intestinal extracts of several mammalian species including pig, rat, dog, and man. The primary structure of rabbit PYY is still unknown, although rabbit tissues have extensively been used for characterization of PYY receptor subtypes and receptor subtype-mediated actions. We report the purification and primary structure of PYY(1-36) (PYY-I) from rabbit intestinal mucosa, and the existence of a second endogenous molecular form of PYY, PYY(3-36) (PYY-II). The amino acid sequence of PYY-I is YPSKPEAPGEDASPEELNRYYASLRHYLNLVTRQRY-amide. Rabbit PYY differs from porcine PYY, which is identical to rat and canine PYY, by two amino acid substitutions at positions 3 (Ser instead of Ala) and 18 (Asp instead of Ser), whereas rabbit PYY and human PYY differ by only one residue at position 3 (Ser instead of Ile). The existence of two endogenous forms of PYY in the rabbit, with PYY-II lacking the amino-terminal dipeptide Tyr-Pro of PYY-I, is consistent with previously reported findings, demonstrating the existence of PYY-II in man and dog (9,11). We have previously demonstrated that PYY-I is an unselective Y1/Y2 agonist, whereas PYY-II is a highly selective Y2 agonist. Thus, proteolytic processing of PYY-I controls the peptide's receptor selectivity. The existence of PYY-I and PYY-II in the rabbit supports the assumption of a physiological role of Y receptor heterogeneity for PYY.

Amino Acid Sequence↗
PubMed1993

Proteolytic processing of neuropeptide Y and peptide YY by dipeptidyl peptidase IV.

Neuropeptide Y, peptide YY and pancreatic polypeptide share an evolutionary conserved proline-rich N-terminal sequence, a structure generally known to be inert to the attack of common proteinases, but a potential target for specialized proline-specific aminopeptidases. Purified human dipeptidyl peptidase IV (also termed CD 26) liberated N-terminal Tyr-Pro from both, neuropeptide Y and peptide YY, with very high specific activities and Km values in the micromolar range, but almost no Ala-Pro from pancreatic polypeptide. Other proline-specific aminopeptidases exhibited low (aminopeptidase P, liberation of N-terminal Tyr) or totally no activity (dipeptidyl peptidase II), as was also observed with less-specific aminopeptidases (aminopeptidase M, leucine aminopeptidase). When human serum was incubated with neuropeptide Y or peptide YY at micro- and nanomolar concentrations, Tyr-Pro was detected as a metabolite of both peptides. Formation of Tyr-Pro in serum was blocked in the presence of Lys-pyrrolidine and diprotin A (Ile-Pro-Ile), specific, competitive inhibitors of dipeptidyl peptidase IV. Incubation of neuropeptide Y or peptide YY with immunocytochemically defined, cultivated endothelial cells from human umbilical cord also yielded Tyr-Pro. Dipeptidyl peptidase IV could be immunostained on most endothelial cells by a specific antibody. We suggest that dipeptidyl peptidase IV might be involved in the degradation of neuropeptide Y and peptide YY to N-terminal truncated neuropeptide Y(3-36) and peptide YY(3-36). Since specific binding to Y1, but not to Y2 subtype of neuropeptide Y/peptide YY receptors requires intact N- as well as C-termini of neuropeptide Y and peptide YY, removal of their amino-terminal dipeptides by dipeptidyl peptidase IV inactivates them for binding to one receptor subtype.

Amino Acid Sequence↗
PubMed1993

[Proteolytic processing by dipeptidyl aminopeptidase IV generates receptor selectivity for peptide YY (PYY)].

Two receptor subtypes, Y1 and Y2, are known to mediate PYY biological activity. PYY 1-36 binds to Y1 and Y2 receptors with equal affinity, whereas the second endogenous form of PYY, PYY 3-36, selectively binds to Y2 receptors. Dipeptidyl cleavage thus transforms an unselective Y agonist into a highly selective Y2 agonist, PYY 3-36. The enzyme responsible for this processing is unknown. Since PYY has a proline in the penultimate position it is protected from the attack of most unspecific exopeptidases. Only a few exopeptidases are theoretically capable of generating PYY 3-36 from PYY 1-36. Of the enzymes tested only the dipeptidyl aminopeptidase IV (DPP IV, E.C. 3.4.14.5) cleaved Tyr-Pro from PYY 1-36 with high activity. Since DPP IV is found on the endothelial surface and brush border membranes it can be considered a candidate enzyme for generating PYY 3-36 in vivo, thereby regulating the ratio of Y1/Y2 receptor stimulation by PYY.

Dipeptidyl Peptidase 4↗
PubMed1993

[The terminal ileum as a co-regulator of cyclic interdigestive pancreatic secretion in man].

Nutrients present in the ileum of humans can modulate endogenously stimulated pancreatic secretion. To determine whether cyclic interdigestive pancreatic secretion can also be influenced by nutrients in the ileum, six fasting volunteers were intubated with an oro-ileal multi-lumen tube for perfusing test and marker solutions, aspiration of duodenal contents and recording of motility. At the beginning of the interdigestive cycle, the ileum was perfused intermittently with solutions of carbohydrates, proteins or lipids in the physiological amounts observed in the ileum after a meal; saline solution was perfused as a control. After saline, protein and calcium perfusion, the expected periodic increase in chymotrypsin secretion was observed during phase II of the interdigestive cycle (p < 0.05 vs phase I). In contrast, carbohydrates and lipids inhibited the phase-II-associated increase in pancreatic secretion. These findings indicate that the ileum may be involved in the regulation of human interdigestive pancreatic secretion.

Adult↗
PubMed1993

[Y1 receptors mediate inhibitory and stimulatory effects of peptide YY in isolated small intestine and large intestine muscles of the rabbit].

Peptide YY has been shown to have stimulatory and inhibitory effects on gastrointestinal motility. However, the receptors mediating these effects are unknown. To determine if specific YY receptor agonists can mediate the effects on gastrointestinal motility we studied the effects of peptide YY (PYY), of Pro34PYY, a selective Y1 agonist, and of PYY 3-36, a selective Y2 agonist, on the motility in isolated smooth muscle strips from rabbit small and large intestine. In strips from distal colon, PYY stimulated spontaneous motility whereas it inhibited spontaneous contractions in circular strips from distal ileum. In distal circular colon maximal inotropic response (10.1 +/- 2.1% of a maximal response to carbachol 10(-5) M) was found at PYY 10(-8) M; (ED50 3.1 +/- 1.2 x 10(-9) M). In distal circular ileum maximal inhibition (by 39 +/- 20% of basal motility index) was found at 10(-7) M; (ID50 6.2 +/- 1.4 x 10(-9) M). PYY caused a dose-dependent inhibition of the on-contraction induced by electrical field stimulation. This inhibition could not be reversed by alpha- or beta-adrenergic blockade. PYY had no influence on the inotropic response evoked by carbachol. Both the stimulatory effect of PYY observed in distal colon and the inhibitory effect in distal ileum could be reproduced by the Y1 agonist Pro34PYY, but not by the Y2 agonist PYY 3-36. In distal circular colon the maximal inotropic response evoked by the Y1 agonist was 10 +/- 1.4%; (ED50 1.2 +/- 0.5 x 10(-8) M).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Comparison of clearance and metabolism of infused cholecystokinins 8 and 58 in dogs.

BACKGROUND: Cholecystokinin (CCK) 58 is the predominant molecular form of CCK in canine and human intestine and circulating blood. There is no report on the metabolism and clearance rate of CCK-58. The aim of this study was to compare the in vivo half-life and metabolism of CCK-58 with that of synthetic CCK-8. METHODS: CCK-58 was purified from canine intestine by consecutive high-performance liquid chromatographic (HPLC) and fast protein liquid chromatographic steps. The peptides were given to 12 dogs as an intravenous (IV) bolus injection to determine the half-life of circulating CCK. Six dogs were given CCK-58 or CCK-8 as a constant IV infusion to determine plasma clearance rates and stability in circulating blood. Circulating molecular forms of CCK were determined by radioimmunoassay after extraction of CCK from plasma and characterization by HPLC. RESULTS: The half-life of CCK-58 was 4.4 +/- 0.6 minutes compared with 1.3 +/- 0.1 minutes for CCK-8. Less than 5% of CCK-58 could be detected as smaller forms during constant IV infusion. CONCLUSIONS: The longer half-life of CCK-58 compared with CCK-8 and the minimal conversion into smaller forms during constant IV infusion are consistent with the finding that CCK-58 is not only the major stored form but also the circulating form of CCK after endogenous stimulation in dogs.

Animals↗
PubMed1992

Novel generation of hormone receptor specificity by amino terminal processing of peptide YY.

The physiological significance of multiple Y receptors has not been determined since until recently only one form of endogenous agonists was known, namely PYY1-36 and NPY1-36. Recently, a new molecular form of PYY was characterized as des(Tyr-Pro)PYY (PYY3-36 or PYY-II). Its ability to interact at various Y receptors was not characterized. Analytical chromatography of fresh canine colon extracts shows two peaks of immunoreactivity eluting in the positions of PYY-II and PYY1-36 (PYY). PYY-II was about 40% of the total PYY immunoreactivity indicating that it is one of the major forms of PYY expressing its biological activity. It is shown that PYY-II will not displace label from the Y1 receptors found on a human neuroblastoma cell line. It is further shown that PYY-II is as potent as PYY for the inhibition of pancreatic secretion, which must occur through Y2 receptors. The enzymatic removal of Tyr-Pro from PYY to form PYY-II must therefore regulate the relative expression of a non-selective agonist (PYY) to a highly selective Y2 agonist (PYY-II). Amino terminal processing of PYY represents a novel type of regulation of peptide hormone specificity. It has important biological implications for PYY and potential relevance for other peptide hormone receptor systems.

Animals↗
PubMed1992

Patterns of prohormone processing. Order revealed by a new procholecystokinin-derived peptide.

An 83-amino acid cholecystokinin peptide with a sulfated tyrosine and an amidated carboxyl terminus (CCK-83) was purified from human intestinal mucosa. The purified peptide was chemically characterized, and its bioactivity was compared to CCK-8. Several post-translational processing steps such as cleavage at basic residues, sulfation, and amidation are necessary to form biologically active cholecystokinin from its nascent prepropeptide. The discovery of CCK-83 gives new insight into the order of preprohormone processing. The processing of prepro-CCK appears to be in the order of: 1) signal peptidase cleavage, 2) tyrosine sulfation, 3) cleavage after a carboxyl-terminal pair of basic residues, 4) carboxypeptidase B-like cleavage of these basic residues, 5) amidation (which results in the formation of CCK-83), and 6) cleavage at monobasic residues by endopeptidases (which results in the smaller molecular forms of cholecystokinin). The characterization of biologically active CCK-83 with a sulfated tyrosine and an amidated carboxyl terminus establishes the site of signal peptidase action and suggests an order of post-translational modifications that give rise to the various molecular forms of cholecystokinin.

Amino Acid Sequence↗
PubMed1991

Determination of various molecular forms of cholecystokinin from canine mucosa by radioimmunoassay and bioassay.

Bioassays using amylase release from isolated pancreatic acini measure only cholecystokinin (CCK) forms with an intact carboxyl terminus ending with phenylalanine amide, but it cannot be excluded that peptides not structurally related to CCK are also responsible for CCK-like bioactivity. CCK exists in several molecular forms in intestinal mucosa which are released into the circulating blood. We studied the molecular forms of CCK in canine intestinal extracts after separation by high performance liquid chromatography by bioassay and compared them with those detected by radioimmunoassay. For the radioimmunoassay, an antibody was used which needs the carboxyl terminal phenylalanine amide for recognition. Three immunoreactive peaks were reproducibly seen in HPLC eluates which eluted in the regions of synthetic CCK-8, purified porcine CCK-33-39 (which co-elute using this gradient) and purified canine CCK-58. All these peaks were bioactive for amylase release from isolated pancreatic acini. No further bioactive peaks were detected in the HPLC eluates. When an antibody was used which recognizes the midregion of CCK-58, an additional peak was detected which eluted between CCK-33-39 and CCK-58. This form presumably represents an amino terminal fragment of CCK lacking the carboxyl terminus. It can be concluded that bioassays of CCK measure only CCK bioactivity in intestinal mucosal extracts, whereas radioimmunoassays may detect biologically inactive forms depending on the antibody recognition site.

Amylases↗
PubMed1990

Characterization of the major form of cholecystokinin in human intestine: CCK-58.

Acid extracts of human intestines obtained from surgical samples or from organ donors contain cholecystokinin (CCK) immunoreactivity. From surgical samples, extracted and eluted quickly, greater than 75% of the CCK immunoreactivity eluted in the same region as purified canine CCK-58 during analytical reverse-phase high-pressure liquid chromatography (HPLC). A major portion of the CCK immunoreactivity from donor intestinal extracts also eluted in this region. This immunoreactivity has been purified from human intestinal extracts by a series of several reverse-phase and cation-exchange chromatographies. Amino acid and microsequence analysis showed that this immunoreactivity is human CCK-58. Tryptic digestion of purified human CCK-58 produced another immunoreactive form that eluted in the position of CCK-8 during analytical reverse-phase HPLC. The immunoreactivity of the trypsin-digested material was 2.6-fold higher than that of an identical sample of CCK-58 incubated without trypsin. Thus the carboxyl-terminal antibody used for radioimmunoassay cross-reacts greater than twofold less with human CCK-58. This diminished cross-reactivity would lead to an underestimation of the relative proportions of CCK-58 in tissue and plasma extracts. If CCK-58 is the major circulating form this diminished cross-reactivity would also lead to underestimations of the circulating levels of total CCK. Determination of human CCK-58 structure confirms that one of the major components of human CCK that expresses biological activity is CCK-58.

Amino Acid Sequence↗
PubMed1990

Molecular variants of cholecystokinin after endogenous stimulation in humans: a time study.

The time-dependent release of molecular variants of cholecystokinin (CCK) into the circulation was studied before and 1, 2, and 4 h after a test meal in six healthy volunteers. At each time period, 100 ml of blood were drawn in a manner to inhibit CCK degradation. Plasma was formed and CCK concentrated by Sep-Pak C18 cartridge chromatography. Molecular variants of CCK and gastrin were well separated from each other by high-performance liquid chromatography (HPLC). Molecular forms of CCK and gastrin were measured by radioimmunoassay using an antibody that requires the presence of the carboxyl-terminal phenylalanine amide for full recognition, implying that biologically active forms were detected. HPLC elution positions of gastrin forms were determined using a gastrin-specific antibody. Chromatographic separation of CCK from gastrin forms was complete, allowing separate integration of gastrin and CCK forms. Therefore no subtraction of gastrin-like immunoreactivity from CCK-like immunoreactivity (CCK-LI) was necessary and CCK-LI could be directly determined. Peaks of CCK-LI were integrated in the column eluates and the plasma concentrations were calculated. Total plasma CCK-LI rose from a value of 2.4 +/- 0.6 pM before the test meal to 6.4 +/- 0.8, 6.6 +/- 0.9, and 5.8 +/- 1.2 pM 1, 2, and 4 h postprandially. The major molecular forms released into the circulation eluted on HPLC in the position of CCK-58 and CCK-39 (which coelutes with CCK-33). Minor amounts were detected in the position of CCK-8. There was no significant difference in the relative proportions of the molecular forms released at the different time periods.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗