Local effect of neurotensin on canine ileal blood flow, and its release by luminal lipid

New Insights in the Control of Fat Homeostasis: The Role of Neurotensin

Neurotensin (NT) is a small peptide with pleiotropic functions, exerting its primary actions by controlling food intake and energy balance. The first evidence of an involvement of NT in metabolism came from studies on the central nervous system and brain circuits, where NT acts as a neurotransmitter, producing different effects in relation to the specific region involved. Moreover, newer interesting chapters on peripheral NT and metabolism have emerged since the first studies on the NT-mediated regulation of gut lipid absorption and fat homeostasis. Intriguingly, NT enhances fat absorption from the gut lumen in the presence of food with a high fat content, and this action may explain the strong association between high circulating levels of pro-NT, the NT stable precursor, and the increased incidence of metabolic disorders, cardiovascular diseases, and cancer observed in large population studies. This review aims to provide a synthetic overview of the main regulatory effects of NT on several biological pathways, particularly those involving energy balance, and will focus on new evidence on the role of NT in controlling fat homeostasis, thus influencing the risk of unfavorable cardio–metabolic outcomes and overall mortality in humans.

Roles of Gut-Derived Secretory Factors in the Pathogenesis of Non-Alcoholic Fatty Liver Disease and Their Possible Clinical Applications

The rising prevalence of non-alcoholic fatty liver disease (NAFLD) parallels the global increase in the number of people diagnosed with obesity and metabolic syndrome. The gut-liver axis (GLA) plays an important role in the pathogenesis of NAFLD/non-alcoholic steatohepatitis (NASH). In this review, we discuss the clinical significance and underlying mechanisms of action of gut-derived secretory factors in NAFLD/NASH, focusing on recent human studies. Several studies have identified potential causal associations between gut-derived secretory factors and NAFLD/NASH, as well as the underlying mechanisms. The effects of gut-derived hormone-associated drugs, such as glucagon-like peptide-1 analog and recombinant variant of fibroblast growth factor 19, and other new treatment strategies for NAFLD/NASH have also been reported. A growing body of evidence highlights the role of GLA in the pathogenesis of NAFLD/NASH. Larger and longitudinal studies as well as translational research are expected to provide additional insights into the role of gut-derived secretory factors in the pathogenesis of NAFLD/NASH, possibly providing novel markers and therapeutic targets in patients with NAFLD/NASH.

Role of intestinal peptides and the autonomic nervous system in postprandial hypotension in patients with multiple system atrophy

Postprandial hypotension (PPH) is a major clinical problem in patients with autonomic failure such as that observed in multiple system atrophy (MSA). The pathophysiology of PPH remains unclear, although autonomic dysfunction and gastrointestinal vasoactive peptides have been suspected to participate in its pathogenesis. We measured blood pressure and plasma levels of glucose, insulin, noradrenaline, neurotensin, glucagon-like peptide (GLP)-1 and GLP-2 before and after meal ingestion in 24 patients with MSA to reveal the roles of the autonomic nervous system and gastrointestinal vasoactive peptides in PPH. We performed a second meal-ingestion test by administering acarbose to evaluate the effects of acarbose (an α-glucosidase inhibitor) on PPH and vasoactive peptides in 14 patients with MSA and PPH. We also evaluated blood pressure responses to the head-up tilt test and heart rate variability in all the patients. Severities of PPH and orthostatic hypotension were significantly correlated. Patients with PPH had significantly worse orthostatic hypotension and lower heart rate variability than those without PPH. Postprandial GLP-1 secretion was higher in patients with PPH than in those without PPH. No significant differences were observed in the postprandial increases in plasma levels of glucose, insulin, noradrenaline, neurotensin or GLP-2. Acarbose significantly attenuated postprandial hypotension and tended to decrease GLP-2 secretion. Our results indicate that autonomic failure is involved in the pathogenesis of PPH and confirm that acarbose has a preventive effect against PPH in patients with MSA. Decreased postprandial secretion of GLP-2, which increases intestinal blood pooling, may attenuate PPH in patients with MSA.

Analysis of antral biopsy specimens for evidence of acquired mucosa-associated lymphoid tissue in HIV1-seropositive and HIV1-negative patients

BACKGROUND

There is conflicting evidence concerning the prevalence of Helicobacter pylori gastritis in HIV1-infected patients. Furthermore, a possible influence of immunodeficiency on the acquisition of mucosa-associated lymphoid tissue (MALT) in the antral mucosa remains to be elucidated.

METHODS

Seventy-seven consecutive HIV1-infected patients (mean age, 40.2 years) were compared in a prospective study with 77 HIV1-negative age-matched patients, using immunohistochemical stainings.

RESULTS

In HIV1-infected patients the prevalence of H. pylori gastritis was lower and the inflammatory reaction less pronounced than in controls. Lymphoid follicles and intraepithelial B cells were significantly more often detected in HIV1-negative patients.

CONCLUSIONS

Evidence of acquired MALT is only rarely found in HIV1-infected patients. These findings might contribute to the explanation of why low-grade gastric MALT lymphomas have not been reported in HIV1-infected patients so far.

Research note: cardiovascular effects of neurotensin in anesthetized White Leghorn hens

Solutions of neurotensin (NT) at 0, 12, 60, 120, and 600 nM were infused i.v. into anesthetized, 16- to 34-wk-old hens at 60 microL/kg per minute for 30 min. These infusates increased plasma NT concentrations to steady state values of about .1, .2, 1, 2, and 10 times the postprandial concentrations of NT in hepatic portal blood, respectively. None of these concentrations significantly affected heart rate or arterial (carotid) or central venous (jugular) blood pressure.

Anesthetic dependence of the inhibitory effect of neurotensin on pentagastrin-stimulated acid secretion in rats. A possible role for somatostatin

The existence of possible local mediators of the inhibitory effect of neurotensin on gastric acid secretion has not been determined. We perfused rats intragastrically with warmed saline and stimulated acid secretion with intravenous pentagastrin, 32 micrograms/kg/hr, and found that anesthesia with pentobarbital resulted in marked inhibition of acid secretion by intravenous neurotensin; however, anesthesia with urethane prevented this inhibitory effect of neurotensin from occurring. In addition, we found a significant increase in somatostatin-like immunoreactivity in portal venous blood during neurotensin infusion in pentobarbital-anesthetized rats. Neither neurotensin nor pentagastrin infusion modified gastric luminal somatostatin-like immunoreactivity after either pentobarbital or urethane, and rats anesthetized with urethane did not show an increase of somatostatin-like immunoreactivity in portal venous blood during neurotensin infusion. These results suggested that somatostatin-like immunoreactivity, released into the portal circulation, was necessary for exogenous neurotensin to inhibit pentagastrin-stimulated gastric acid secretion under these conditions in anesthetized rats.

Inhibitory effect of neurotensin on gastric acid secretion in rats. Development of a bioassay model

Neurotensin has been shown to inhibit gastric acid secretion when administered in pharmacological doses, but no information has been available concerning its possible dose-related effect during intravenous infusion. In this study, a dose-related and reversible inhibitory effect of neurotensin was demonstrated in pentobarbital-anesthetized female Sprague-Dawley rats. The rats underwent continuous gastric perfusion with saline, 1 ml/min, and intravenous infusion of both pentagastrin and neurotensin. Inhibition of acid secretion did not depend upon the occurrence of hypotension, and ranged from 35 +/- 7% of maximal acid output at 0.24 nmol/kg/hr to 60 +/- 10% at 7.2 nmol/kg/hr of neurotensin. Blood levels of C-terminal neurotensin-like immunoreactivity were proportional to the dose of peptide infused and were 52 fmol/ml during infusion of 0.24 nmol/kg/hr, a dose that significantly inhibited pentagastrin-induced acid secretion. Thus, a model has been developed to study the effect of neurotensin infusion on acid secretion; the concentration of plasma neurotensin-like immunoreactivity at which inhibition occurs in this model is similar to the concentration reported to occur after a nutrient stimulus.