Central alpha 2-adrenoceptor-mediated inhibition of gastric motility in rats

Dual Alpha2C/5HT1A Receptor Agonist Allyphenyline Induces Gastroprotection and Inhibits Fundic and Colonic Contractility

BACKGROUND

Allyphenyline, a novel α2-adrenoceptor (AR) ligand, has been shown to selectively activate α2C-adrenoceptors (AR) and 5HT1A receptors, but also to behave as a neutral antagonist of α2A-ARs. We exploited this unique pharmacological profile to analyze the role of α2C-ARs and 5HT1A receptors in the regulation of gastric mucosal integrity and gastrointestinal motility.

METHODS

Gastric injury was induced by acidified ethanol in Wistar rats. Mucosal catalase and superoxide dismutase levels were measured by assay kits. The effect of allyphenyline on electrical field stimulation (EFS)-induced fundic and colonic contractions was determined in C57BL/6 mice.

RESULTS

Intracerebroventricularly injected allyphenyline (3 and 15 nmol/rat) dose dependently inhibited the development of mucosal damage, which was antagonized by ARC 239 (α2B/C-AR and 5HT1A receptor antagonist), (S)-WAY 100135 (selective 5HT1A receptor antagonist), and JP-1302 (selective α2C-AR antagonist). This protection was accompanied by significant elevation of mucosal catalase and superoxide dismutase levels. Allyphenyline (10(-9)-10(-5) M) also inhibited EFS-induced fundic contractions, which was antagonized by ARC 239 and (S)-WAY 100135, but not by JP-1302. Similar inhibition was observed in the colon; however, in this case only ARC 239 reduced this effect, while neither selective inhibition of α2C-ARs and 5HT1A receptors nor genetic deletion of α2A- and α2B-ARs influenced it.

CONCLUSIONS

Activation of both central α2C-ARs and 5HT1A receptors contributes to the gastroprotective action of allyphenyline in rats. Its inhibitory effect on fundic contractions is mediated by 5HT1A receptors, but neither α2-ARs nor 5HT1A receptors take part in its inhibitory effect on colonic contractility in mice.

A review of enteral strategies in infant short bowel syndrome: evidence-based or NICU culture?

INTRODUCTION

Short bowel syndrome (SBS) is an increasingly common condition encountered across neonatal intensive care units. Improvements in parenteral nutrition (PN), neonatal intensive care and surgical techniques, in addition to an improved understanding of SBS pathophysiology, have contributed in equal parts to the survival of this fragile subset of infants. Prevention of intestinal failure associated liver disease (IFALD) and promotion of intestinal adaptation are primary goals of all involved in the care of these patients. While enteral nutritional and pharmacological strategies are necessary to achieve these goals, there remains great variability in the application of therapeutic strategies in units that are not necessarily evidence-based.

MATERIALS AND METHODS

A search of major English language medical databases (SCOPUS, Index Medicus, Medline, and the Cochrane database) was conducted for the key words short bowel syndrome, medical management, nutritional management and intestinal adaptation. All pharmacological and nutritional agents encountered in the literature search were classified based on their effects on absorptive capacity, intestinal adaptation and bowel motility that are the three major strategies employed in the management of SBS. The Oxford Center for Evidence-Based Medicine (CEBM) classification for levels of evidence was used to develop grades of clinical recommendation for each variable studied.

RESULTS

We reviewed various medications used and nutritional strategies included soluble fiber, enteral fat, glutamine, probiotics and sodium supplementation. Most interventions have scientific rationale but little evidence to support their role in the management of infant SBS. While some of these agents symptomatically improve diarrhea, they can adversely influence pancreatico-biliary function or actually impair intestinal adaptation. Surgical anatomy and liver function are two important variables that should determine the selection of pharmacological and nutritional interventions.

DISCUSSION

There is a paucity of research investigating optimal clinical practice in infant SBS and the little evidence available is consistently of lower quality, resulting in a wide variation of clinical practices among NICUs. Prospective trials should be encouraged to bridge the evidence gap between research and clinical practice to promote further progress in the field.

Central neural responses to restraint stress are altered in rats with an early life history of repeated brief maternal separation

Repeated brief maternal separation (i.e. 15 min daily, MS15) of rat pups during the first one to two postnatal weeks enhances active maternal care received by the pups and attenuates their later behavioral and neuroendocrine responses to stress. In previous work, we found that MS15 also alters the developmental assembly and later structure of central neural circuits that control autonomic outflow to the viscera, suggesting that MS15 may alter central visceral circuit responses to stress. To examine this, juvenile rats with a developmental history of either MS15 or no separation (NS) received microinjection of retrograde neural tracer, FluoroGold (FG), into the hindbrain dorsal vagal complex (DVC). After 1 week, FG-injected rats and surgically intact littermates were exposed to either a 15-min restraint stress or an unrestrained control condition, and then perfused 1 h later. Brain tissue sections from surgically intact littermates were processed for Fos alone or in combination with phenotypic markers to examine stress-induced activation of neurons within the paraventricular nucleus of the hypothalamus (PVN), bed nucleus of the stria terminalis (BNST), and hindbrain DVC. Compared to NS controls, MS15 rats displayed less restraint-induced Fos activation within the dorsolateral BNST (dBNST), the caudal PVN, and noradrenergic neurons within the caudal DVC. To examine whether these differences corresponded with altered neural inputs to the DVC, sections from tracer-injected rats were double-labeled for FG and Fos to quantify retrogradely labeled neurons within hypothalamic and limbic forebrain regions of interest, and the proportion of these neurons activated after restraint. Only the dBNST displayed a significant effect of postnatal experience on restraint-induced Fos activation of DVC-projecting neurons. The distinct regional effects of MS15 on stress-induced recruitment of neurons within hypothalamic, limbic forebrain, and hindbrain regions has interesting implications for understanding how early life experience shapes the functional organization of stress-responsive circuits.

Central serotonergic and noradrenergic receptors in functional dyspepsia

Functional dyspepsia is a symptom complex characterised by upper abdominal discomfort or pain, early satiety, motor abnormalities, abdominal bloating and nausea in the absence of organic disease. The central nervous system plays an important role in the conducting and processing of visceral signals. Alterations in brain processing of pain, perception and affective responses may be key factors in the pathogenesis of functional dyspepsia. Central serotonergic and noradrenergic receptor systems are involved in the processing of motor, sensory and secretory activities of the gastrointestinal tract. Visceral hypersensitivity is currently regarded as the mechanism responsible for both motor alterations and abdominal pain in functional dyspepsia. Some studies suggest that there are alterations in central serotonergic and noradrenergic systems which may partially explain some of the symptoms of functional dyspepsia. Alterations in the autonomic nervous system may be implicated in the motor abnormalities and increases in visceral sensitivity in these patients. Noradrenaline is the main neurotransmitter in the sympathetic nervous system and again alterations in the functioning of this system may lead to changes in motor function. Functional dyspepsia causes considerable burden on the patient and society. The pathophysiology of functional dyspepsia is not fully understood but alterations in central processing by the serotonergic and noradrenergic systems may provide plausible explanations for at least some of the symptoms and offer possible treatment targets for the future.

Clonidine pretreatment inhibits stress-induced gastric ulcer in rats

We studied the effects of clonidine (0.5 mg/kg) on hormonal stress response and antioxidant enzymes cold restraint-induced gastric lesions in rats. Rats in the study group were given 0.5 mg/kg intraperitoneal clonidine (n = 12), whereas the control group received 0.5 mL/kg intraperitoneal isotonic sodium chloride solution (n = 9). Animals were then subjected to immobilization at 4 degrees C in restraining devices for 4 h after a starvation period of 24 h. Gastric lesion index, gastric tissue malondialdehyde activity, and plasma cortisol concentrations were assayed. Histopathologic examination demonstrated a stress ulcer index of 3.17+/-0.92 mm in the clonidine group and 14.0+/-3.22 mm in the control group (P<0.05). The tissue malondialdehyde concentrations were slightly higher in the control group than in the clonidine group, but the differences were not statistically significant (P>0.05). Plasma cortisol levels were lower in the clonidine group (P<0.05). We concluded that clonidine attenuated the tissue damage and stress response in stress-induced gastric ulceration.

IMPLICATIONS

Stressful circumstances can cause stomach ulcers, which can bleed, exposing patients to potentially life-threatening complications. In the present animal study, we showed that clonidine, a routinely available medication, may be useful in preventing stress-induced stomach ulcers.