Central neurotensin protects the mucosa by a prostaglandin-mediated mechanism and inhibits gastric acid secretion in the rat

Gastric mucosal levels of prostaglandins and leukotrienes in patients with gastric ulcer after treatment with rabeprazole in comparison to treatment with ranitidine

AIM

Prostaglandins (PGs) and leukotrienes (LTs) are major factors involved in the defense of the gastric mucosa against ulcer formation. However, little is still known about the gastromucosa-protecting action of proton pump inhibitors (PPIs) and histamine H(2) receptor antagonists (H(2) blockers) in patients with gastric ulcer. We therefore examined the effectiveness of a PPI in protecting the gastric mucosa.

METHODS

We compared the PGE(2) and LTB(4) levels and the expression levels of cyclooxygenase (COX)-1 and COX-2 mRNA in the gastric mucosa in gastric ulcer patients between the group treated for 8 weeks with a PPI, rabeprazole (PPI group; n=5), and the group treated for 8 weeks with an H(2) blocker, ranitidine (H(2) blocker group; n=6), as well as in nonulcer subjects (control group; n=5).

RESULTS

The mucosal levels of PGE(2) and COX-2 mRNA expression were significantly lower in the ulcer patients than those in the nonulcer patients, whereas the LTB(4) level was significantly higher in the ulcer patients than that in the nonulcer patients, and it was also significantly lower in the ulcerated mucosa than that in the nonulcerated mucosa. The PPI group had a significantly increased PGE(2) and decreased LTB(4) levels in comparison to the H(2) blocker group during the ulcer-healing stage. The COX-1 mRNA expression showed no difference among the PPI and H(2) blocker groups or between before and after the treatment. However, the COX-2 mRNA expression increased in the PPI group more than that in the H(2) blocker group during the ulcer-healing stage.

CONCLUSION

These findings demonstrated the significant gastric-mucosa-protecting effect of PPI by increasing the PGE(2) production and reducing the LTB(4) production.

Mesolimbic expression of neurotensin and neurotensin receptor during stress-induced gastric mucosal injury

Neurotensin is a neurotransmitter present in the brain and gastrointestinal tract. Intracerebroventricular injection of neurotensin protects rats from gastric mucosal injury caused by cold water restraint (CWR). Direct injection of neurotensin into the nucleus accumbens (NACB), part of the mesolimbic dopamine system, reduces gastric mucosal injury, suggesting that neurotensin confers protection on the mucosa through interaction with the mesolimbic system. The hypothesis is that the concentration of neurotensin in the mesolimbic system decreases during CWR, affecting the expression of neurotensin and the neurotensin receptor. After 1 h of CWR, neurotensin concentration significantly decreased 41% in the NACB and returned toward control concentrations after 2 h of CWR. The concentration of neurotensin mRNA significantly decreased 46% after 1 h CWR and returned toward control after 2 h. In contrast, neurotensin binding sites in the NACB increased from 159 to 228 fmol/mg protein after 1 h of CWR and increased significantly to 280 fmol/mg protein after 2 h CWR, whereas the level of neurotensin receptor mRNA significantly decreased 51 and 50% at 1 and 2 h, respectively. These studies show that neurotensin concentration within the mesolimbic system is transiently reduced by CWR stress and that the number of neurotensin binding sites increases, presumably in response to the decrease in neurotensin.

Inhibition of gastric acid secretion by stress: a protective reflex mediated by cerebral nitric oxide

Moderate somatic stress inhibits gastric acid secretion. We have investigated the role of endogenously released NO in this phenomenon. Elevation of body temperature by 3 degrees C or a reduction of 35 mmHg (1 mmHg = 133 Pa) in blood pressure for 10 min produced a rapid and long-lasting reduction of distension-stimulated acid secretion in the rat perfused stomach in vivo. A similar inhibitory effect on acid secretion was produced by the intracisternal (i.c.) administration of oxytocin, a peptide known to be released during stress. Intracisternal administration of the NO-synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME) reversed the antisecretory effect induced by all these stimuli, an action prevented by intracisternal coadministration of the NO precursor, L-arginine. Furthermore, microinjection of L-NAME into the dorsal motor nucleus of the vagus nerve reversed the acid inhibitory effects of mild hyperthermia, i.v. endotoxin, or i.c. oxytocin, an action prevented by prior microinjection of L-arginine. By contrast, microinjection of L-NAME into the nucleus tractus solitarius failed to affect the inhibitory effects of hyperthermia, i.v. endotoxin, or i.c. oxytocin. Immunohistochemical techniques demonstrated that following hyperthermia there was a significant increase in immunoreactivity to neuronal NO synthase in different areas of the brain, including the dorsal motor nucleus of the vagus. Thus, our results suggest that the inhibition of gastric acid secretion, a defense mechanism during stress, is mediated by a nervous reflex involving a neuronal pathway that includes NO synthesis in the brain, specifically in the dorsal motor nucleus of the vagus.

CNS effects on gastric functions: from clinical observations to peptidergic brain-gut interactions

Clinical observations as early as the last century pointed to the stomach's link to the brain. Animal studies in this century have given us detailed information about the neuroanatomical and neurophysiological basis of brain-gut interactions. Psychological stress models and stereotaxic brain procedures have been important tools in gaining this information. During the last 10 years, there has been much focus on the effects of neuropeptides on gastric functions. Several CNS-peptides have indeed been shown to influence multiple gastric functions such as: acid secretion, bicarbonate secretion, mucus secretion, motility, blood flow and prostaglandin synthesis. Accordingly, direct CNS-application of these peptides also influences the development of gastric erosions during experimental stress procedures.

The neurobiology of stress ulcers

We have reviewed the neurobiology of stress ulcers from animal models to potential pharmacotherapeutic mechanisms. The evidence strongly supports the hypothesis that certain stress-related gastric lesions are 'brain-driven' events which may be more effectively managed through central manipulations than by altering local, gastric factors. Recent advances in the use of anxiolytic and antidepressant drugs in the management of stress-related gastric mucosal injury further supports the contention that a brain-gut axis, which may have nervous, peptidergic and classic monoaminergic components, modulates the intricate and complicated pattern of communication between the brain and the stomach. Delineation of the precise pathways which make up this communication as well as their manipulation by various pharmacological agents will be the focus of future research endeavour.