Amitriptyline modifies the visceral hypersensitivity response to acute stress in the irritable bowel syndrome

BACKGROUND

Acute physical stress causes alteration in gut autonomic function and visceral hypersensitivity in patients with irritable bowel syndrome (IBS). We have developed a model to measure this stress response.

AIM

To assess whether treatment with a drug effective in treating IBS (amitriptyline) alters the response to acute stress in IBS patients.

METHODS

Nineteen patients with IBS were given amitriptyline 25-50 mg. Patients underwent physical stress (cold pressor) test at baseline and after 3 months of treatment. Physiological parameters measured were: stress perception; systemic autonomic tone [heart rate (HR) and blood pressure (BP)]; gut specific autonomic innervation [rectal mucosal blood flow (RMBF)] and visceral sensitivity (rectal electrosensitivity).

RESULTS

Fourteen of 19 (74%) patients improved symptomatically after 3 months of amitriptyline. Acute stress induced increased perception of stress and systemic autonomic tone and reduced RMBF in symptomatic responders and nonresponders (P > 0.05 for all). All nonresponders but only 3 of 14 responders continued to exhibit stress-induced reduced pain threshold at 3 months (change from baseline -31% vs. +2%, P < 0.03 respectively).

CONCLUSION

In this open study, amitriptyline appears to decrease stress-induced electrical hypersensitivity; this effect is independent of autonomic tone. The gut response to acute stress deserves further study as a model to study drug efficacy in IBS.

Pharmacological modulation of gut mucosal and large vessel blood flow

BACKGROUND

Constipation, diminished gut blood flow, ischaemic colitis and drug therapy may be associated.

AIM

To study the effect of constipating medication on, and the regulation of, gut blood flow.

METHODS

24 healthy females (mean age 30) received, in a double-blind, three-way crossover study: (i) placebo, (ii) ipratropium 40 microg by inhalation (positive control known to reduce rectal mucosal blood flow) and (iii) oral loperamide 4 mg. Mucosal blood flow was measured at the splenic flexure and rectum using laser Doppler flowmetry. Blood flow in the superior and inferior mesenteric arteries was measured by trans-abdominal Doppler ultrasound.

RESULTS

Ipratropium decreased rectal mucosal blood flow by 16% (P=0.009) and splenic flexure mucosal blood flow by 8% (P=0.075). Loperamide caused no change in rectal (P=0.40) or splenic flexure mucosal blood flow (P=0.73). Neither treatment changed superior or inferior mesenteric artery blood flow. Splenic flexure mucosal blood flow showed a positive correlation with rectal mucosal blood flow (r=0.69; P<0.0001).

CONCLUSIONS

Vasoactive agents may reduce gut mucosal blood flow in the absence of reduced large vessel flow. Constipating drugs do not necessarily reduce gut blood flow. Rectal mucosal blood flow correlates with splenic flexure mucosal flow, and potentially may be used as a more convenient surrogate for studying splenic flexure blood flow.

Ghrelin augments afferent response to distension in rat isolated jejunum

Ghrelin has been shown to decrease firing of gastric vagal afferents at doses comparable with circulating levels in the fasted state. This raises the possibility that ghrelin may have a hormonal action on other vagal afferent populations. The aim of this study was to determine the effects of ghrelin on jejunal afferent activity; including responses to distension, 2-methyl-5-hydroxytryptamine (2-methyl-5-HT) and cholecystokinin (CCK) in both naïve and vagotomized rats. Ghrelin significantly augmented the afferent response to distension. No effect was observed on baseline afferent discharge, or the response to 2-methyl-5-HT and CCK. The effect of ghrelin was more pronounced at lower ramp distending pressures (0-30 mmHg). Similarly, ghrelin augmented the jejunal afferent responses to phasic distension at 10-30 mmHg, but had no effect at higher pressures. Chronic subdiaphragmatic vagotomy and administration of the growth hormone secretagogue receptor (GHS-R) antagonist [D-Lys3]-GHRP-6 prevented the augmentation of the afferent responses to distension indicating ghrelin is acting through the GHS-R on vagal afferent fibres. Ghrelin augments the mechanosensation of jejunal vagal afferents and hence may lead to increased perception of hunger contractions.

Ghrelin enhances gastric emptying in diabetic gastroparesis: a double blind, placebo controlled, crossover study

BACKGROUND

Diabetic gastroparesis is a disabling condition with no consistently effective treatment. In animals, ghrelin increases gastric emptying and reverses postoperative ileus. We present the results of a double blind, placebo controlled, crossover study of ghrelin in gastric emptying in patients with diabetic gastroparesis.

METHODS

Ten insulin requiring diabetic patients (five men, six type I) referred with symptoms indicative of gastroparesis received a two hour infusion of either ghrelin (5 pmol/kg/min) or saline on two occasions. Blood glucose was controlled by euglycaemic clamp. Gastric emptying rate (GER) was calculated by real time ultrasound following a test meal. Blood was sampled for ghrelin, growth hormone (GH), and pancreatic polypeptide (PP) levels. Cardiovagal neuropathy was assessed using the Mayo Clinic composite autonomic severity score (range 0 (normal)-3).

RESULTS

Baseline ghrelin levels were mean 445 (SEM 36) pmol/l. Ghrelin infusion achieved a peak plasma level of 2786 (188) pmol/l at 90 minutes, corresponding to a peak GH of 70.9 (19.8) pmol/l. Ghrelin increased gastric emptying in seven of 10 patients (30 (6)% to 43 (5)%; p = 0.04). Impaired cardiovagal tone correlated inversely with peak postprandial PP values (p < 0.05) but did not correlate with GER.

CONCLUSIONS

Ghrelin increases gastric emptying in patients with diabetic gastroparesis. This is independent of vagal tone. We propose that analogues of ghrelin may represent a new class of prokinetic agents.