Effect of synthetic neuromedin-N, a novel neurotensin-like peptide, on exocrine pancreatic secretion and splanchnic blood flow in dogs

Lactiplantibacillus plantarum Y44 Complex Fermented Milk Regulates Lipid Metabolism in Mice Fed with High-Fat Diet by Modulating Gut Microbiota

The benefits of fermented milk containing Lactiplantibacillus plantarum (L. plantarum) Y44, known for its weight loss properties, remain unclear. For this, we evaluated the effects of the complex fermented milk (Y44-CFM), obtained through the cofermentation of cow's milk and soybean milk with L. plantarum Y44 and traditional starters, on high-fat diet (HFD)-fed C57BL/6 mice. Our study found that the oral administration of Y44-CFM significantly reduced body weight gain and hepatic lipid accumulation in HFD-fed mice while also mitigating liver injury. Additionally, Y44-CFM regulated the expression of enzymes associated with lipid metabolism in the serum, as well as the corresponding or related genes in the liver, such as fatty acid synthase. Furthermore, HFD-induced systemic inflammation, oxidative stress, and intestinal barrier dysfunction were improved. The primary alterations in hepatic metabolism involved glycerophospholipids and amino acids, including the biosynthesis of valine, leucine, and isoleucine. The diversity and overall structure of the gut microbiota were also regulated, resulting in a significant decrease in the ratio of Firmicutes to Bacteroidetes (F/B) and unclassified_f_Lachnospiraceae, along with a notable increase in Oscillospiraceae. The correlation analysis indicated that Y44-CFM influenced hepatic lipid metabolism by mediating intestinal flora and its production of short-chain fatty acids, ultimately leading to weight reduction.

Pancreatic Blood Flow with Special Emphasis on Blood Perfusion of the Islets of Langerhans

The pancreatic islets are more richly vascularized than the exocrine pancreas, and possess a 5- to 10-fold higher basal and stimulated blood flow, which is separately regulated. This is reflected in the vascular anatomy of the pancreas where islets have separate arterioles. There is also an insulo-acinar portal system, where numerous venules connect each islet to the acinar capillaries. Both islets and acini possess strong metabolic regulation of their blood perfusion. Of particular importance, especially in the islets, is adenosine and ATP/ADP. Basal and stimulated blood flow is modified by local endothelial mediators, the nervous system as well as gastrointestinal hormones. Normally the responses to the nervous system, especially the parasympathetic and sympathetic nerves, are fairly similar in endocrine and exocrine parts. The islets seem to be more sensitive to the effects of endothelial mediators, especially nitric oxide, which is a permissive factor to maintain the high basal islet blood flow. The gastrointestinal hormones with pancreatic effects mainly influence the exocrine pancreatic blood flow, whereas islets are less affected. A notable exception is incretin hormones and adipokines, which preferentially affect islet vasculature. Islet hormones can influence both exocrine and endocrine blood vessels, and these complex effects are discussed. Secondary changes in pancreatic and islet blood flow occur during several conditions. To what extent changes in blood perfusion may affect the pathogenesis of pancreatic diseases is discussed. Both type 2 diabetes mellitus and acute pancreatitis are conditions where we think there is evidence that blood flow may contribute to disease manifestations. © 2019 American Physiological Society. Compr Physiol 9:799-837, 2019.

Synthesis and binding characteristics of [(3)H]neuromedin N, a NTS2 receptor ligand

Neurotensin (NT) and its analog neuromedin N (NN) are formed by the processing of a common precursor in mammalian brain tissue and intestines. The biological effects mediated by NT and NN (e.g. analgesia, hypothermia) result from the interaction with G protein-coupled receptors. The goal of this study consisted of the synthesis and radiolabeling of NN, as well as the determination of the binding characteristics of [(3)H]NN and G protein activation by the cold ligand. In homologous displacement studies a weak affinity was determined for NN, with IC50 values of 454nM in rat brain and 425nM in rat spinal cord membranes. In saturation binding experiments the Kd value proved to be 264.8±30.18nM, while the Bmax value corresponded to 3.8±0.2pmol/mg protein in rat brain membranes. The specific binding of [(3)H]NN was saturable, interacting with a single set of homogenous binding sites. In sodium sensitivity experiments, a very weak inhibitory effect of Na(+) ions was observed on the binding of [(3)H]NN, resulting in an IC50 of 150.6mM. In [(35)S]GTPγS binding experiments the Emax value was 112.3±1.4% in rat brain and 112.9±2.4% in rat spinal cord membranes and EC50 values of 0.7nM and 0.79nM were determined, respectively. NN showed moderate agonist activities in stimulating G proteins. The stimulatory effect of NN could be maximally inhibited via use of the NTS2 receptor antagonist levocabastine, but not by the opioid receptor specific antagonist naloxone, nor by the NTS1 antagonist SR48692. These observations allow us to conclude that [(3)H]NN labels NTS2 receptors in rat brain membranes.

Differential catabolic fate of neuromedin N and neurotensin in the canine intestinal mucosa

We have established the peptidase content of a P2 fraction (enriched in synaptosomes) and plasma membranes prepared from canine intestinal mucosa. Fourteen exo- and endopeptidases were assayed with fluorimetric or chromogenic substrates and identified by means of specific peptidase inhibitors. Post-proline dipeptidyl aminopeptidase IV, aminopeptidase M, and carboxypeptidase A were the most abundant exopeptidases, while aminopeptidases A and B, dipeptidyl aminopeptidase, pyroglutamyl peptide hydrolase I, and carboxypeptidase B displayed little, if any, activity. Endopeptidase 24.11 was the only endopeptidase that was detected in high amount. By contrast, proline endopeptidase exhibited a low activity, while angiotensin-converting enzyme, endopeptidase 24.15, endopeptidase 24.16, and cathepsin B and D-like activities were not detected. The catabolic rates of the two related neuropeptides, neurotensin (NT) and neuromedin N (NN), established that NN was inactivated 16 to 24 times faster than NT by plasma membrane and P2 fractions, respectively. Furthermore, the two peptides underwent qualitatively distinct mechanisms of degradation. A phosphoramidon-sensitive formation of NT(1-10) was detected as the major NT catabolite, indicating that NT was susceptible to an endoproteolytic cleavage elicited by endopeptidase 24.11. By contrast, NN was inactivated by the action of an exopeptidase at its N-terminus, leading to the formation of [des-Lys1]NN. The occurrence of this NN metabolite was prevented by bestatin and actinonin, but not by the aminopeptidase B inhibitor, arphamenine B, indicating that the release of the N-terminal residue of NN was likely due to aminopeptidase M.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of synthetic porcine neuropeptide Y (NPY) on splanchnic blood flows and exocrine pancreatic secretion in dogs

This study examined the effect of synthetic porcine neuropeptide Y on the splanchnic blood flows and the exocrine pancreatic secretion in dogs. Graded doses of neuropeptide Y (0.1-5 microg/kg, intravenous) caused dose-dependent reduction of the secretin-stimulated exocrine pancreatic secretion and of the blood flows in the superior mesenteric artery, the portal vein, and the pancreatic tissue. Neuropeptide Y at 5 microg/kg reduced the blood flows to 45.9 +/- 13.3% (superior mesenteric artery), 63.0 +/- 10.5% (portal vein), and 77.9 +/- 4.8% (pancreatic tissue), respectively. This dose also reduced secretin-stimulated pancreatic juice volume and CCK-8 plus secretin-stimulated protein output to 65.2 +/- 9.3 and 63.3 +/- 14.0%, respectively. This study shows a potent vasoconstrictor effect of neuropeptide Y on splanchnic vessels. Neuropeptide Y also inhibited exocrine pancreatic secretion in a significant correlation with the reduction in pancreatic tissue blood flow, which suggests that reduction in the blood flow may be one of the possible mechanisms of the inhibitory action of neuropeptide Y on exocrine secretion.

Neuromedin-N inhibits migrating myoelectric complex and induces irregular spiking in the small intestine of rats; comparison with neurotensin

The effects of neuromedin-N on migrating myoelectric complexes in the small intestine of rats were studied. As neuromedin-N and neurotensin are structurally related peptides a comparison with neurotensin was made. Myoelectric activity was recorded by means of three bipolar electrodes implanted into the wall of the small intestine at 5, 15 and 25 cm distal to the pylorus. The peptides were administered as intravenous infusions to fasted conscious rats. Neuromedin-N at doses of 100-800 pmol kg-1 min-1 caused a dose-dependent disruption of the migrating myoelectric complexes and induced irregular spiking activity (n = 7, P less than 0.05). Neurotensin induced a similar response, but at doses of 1.0-8.0 pmol kg-1 min-1 (n = 5, P less than 0.05). Thus, on a molar basis, neuromedin-N appeared to be about 100-times less potent than neurotensin. Hexamethonium (20 mg kg-1 i.v.) inhibited the migrating motor complexes and induced quiescence, but did not block the effect of neuromedin-N at a dose of 800 pmol kg-1 min-1. Atropine (1 mg kg-1 i.v.) and mepyramine (2 mg kg-1 i.v.) did not affect the migrating motor complexes, nor did they block the effect of neuromedin-N. Simultaneous infusion of neuromedin-N and neurotensin in a 1:1 molar ratio at doses of 2 pmol kg-1 min-1 showed inhibition of the response to neurotensin in eight out of ten experiments. In conclusion, neuromedin-N changes the myoelectric activity in the small intestine from a fasting to a fed pattern.(ABSTRACT TRUNCATED AT 250 WORDS)

Histamine secretion induced by neuromedin-N

Neuromedin-N dose-dependently stimulated the release of histamine from rat serosal mast cells and was 10 to 100 times less potent than neurotensin. The threshold concentration was 10(-6) M, and 10(-3) M neuromedin-N released 31% of the total cell histamine content. The histamine release induced by neuromedin-N was temperature-dependent with an optimum around 30-37 degrees C. Skin vascular permeability increased dose-dependently in response to intradermal injections of neuromedin-N and this peptide was 10 to 100 times less potent than neurotensin. Mepyramine inhibited the effect on vascular permeability suggesting that the effect of neuromedin-N was mediated via the release of histamine.

Comparison of neuromedin-N and neurotensin on net fluid flux across rat small intestine

Neuromedin-N, a hexapeptide recently isolated and purified from porcine spinal cord, has close sequence homology with the C-terminal region of the tridecapeptide neurotensin. Both peptides have a remarkably similar peripheral distribution. Little is known of the biological activity of neuromedin-N. Neurotensin and peptide histidine methionine are known to stimulate net fluid secretion into rat small intestine. We have therefore tested the effect of neuromedin-N and the hexapeptide neurotensin-(8-13), the smallest fully active analogue of neurotensin in this system, compared with that of neurotensin and peptide histidine methionine. All four peptides reduced net absorption in low doses and caused net secretion in larger doses. However, whereas peptide histidine methionine was active in all areas of the small intestine, neurotensin, neurotensin-(8-13) and neuromedin-N were inactive in the duodenum. In the post-duodenal areas neurotensin was approximately 7 times more active than peptide histidine methionine, 21 times more potent than neuromedin-N and 33 times more potent than neurotensin-(8-13).

Effect of human epidermal growth factor (hEGF) on splanchnic circulation in dogs

The effect of intravenous administration of human epidermal growth factor on the splanchnic blood flows was examined in anesthetized dogs, using an ultrasonic transit-time volume flow meter. Human epidermal growth factor (0.1, 0.5 and 1 microgram/kg) significantly increased blood flows in the portal vein (36.9 +/- 7.4% at 1 microgram/kg) and the superior mesenteric artery (49.0 +/- 16.8% at 1 microgram/kg). Systemic blood pressure monitored simultaneously was significantly decreased (8.4 +/- 1.2% at 1 microgram/kg). This study is the first to demonstrate that intravenous administration of epidermal growth factor increases the portal venous blood flow.

Effects of synthetic kassinin on splanchnic circulation and exocrine pancreas in dogs

Effects of intravenously administered synthetic kassinin on splanchnic circulation and exocrine pancreatic secretion were examined in six anesthetized dogs. Kassinin caused dose-related increases in the blood flow in superior mesenteric artery and portal vein, and produced an initial increase followed by a decrease in pancreatic blood flow, but did not affect the exocrine pancreatic secretion. This study demonstrates that kassinin affects splanchnic blood flow in dogs, and suggests that kassinin or a kassinin-like substance functions as a neuropeptide controlling the splanchnic circulation in mammalian species.

Effect of natural peptide YY on blood flow and exocrine secretion of pancreas in dogs

Little is known regarding the mechanism by which peptide YY exerts an inhibitory effect on exocrine pancreatic secretion. The purpose of this study is to determine if peptide YY affects pancreatic blood flow with simultaneous measurement of exocrine pancreatic secretion in dogs. Pancreatic blood flow was measured by a laser Doppler flowmeter which allows continuous measurement of tissue blood flow. Natural peptide YY (0.1, 0.5, 1 microgram/kg) was infused intravenously as a bolus under background infusion of secretin (1 unit/kg/hr) in combination with cholecystokinin-octapeptide (0.1 microgram/kg/hr). Peptide YY caused a reduction of pancreatic blood flow in a dose-dependent manner as well as inhibition of pancreatic protein output, attaining the maximal reduction (28 +/- 4%) and inhibition (45 +/- 9%) at a dose of 1 microgram/kg, respectively. Simultaneous and continuous observation on tissue blood flow and exocrine secretion of the pancreas revealed that there was a highly significant correlation between the percent reduction of pancreatic blood flow and that of volume of pancreatic juice in response to peptide YY (r = 0.849, P less than 0.001). This study provides evidence that the mechanism of peptide YY-induced inhibition of exocrine pancreatic secretion is mediated, at least partly, through the decreased pancreatic blood flow.

Effects of intravenous ethanol on hepatic and pancreatic blood flow in dogs

Changes in hepatic and pancreatic blood flow in response to ethanol infusion were determined simultaneously and continuously in anesthetized dogs, using a transit-time ultrasonic flowmeter and a laser-Doppler flowmeter. In addition, the effect of intravenous ethanol on exocrine pancreatic secretion was investigated. With a background infusion of secretin, ethanol (1.3 g/kg body wt) was infused intravenously over a 40-min period. Ethanol infusion significantly increased blood flow in the common hepatic artery (by 49%, at the time of the cessation of ethanol infusion), and this increased flow was maintained for 60 min after the cessation of ethanol infusion. In contrast, blood flow in the portal vein was not altered significantly by ethanol. Pancreatic blood flow and secretion showed no significant difference from those seen in the controls. Our data suggest that intravenous ethanol induces a redistribution of the splanchnic blood flow. The increased hepatic arterial flow seen in response to ethanol may play an important role in preventing ethanol-induced hypoxic liver damage.