Susceptibility to adenosine agonists of giant migrating contraction induced by glycerol enema in anesthetized rats

Intracolonic glycerol induces abdominal contractions in rats: role of 5-HT3 receptors

Serotonin and 5-HT3 receptors may be involved in the activation of nociceptive afferent pathways by rectal distension. In rats, intracolonic infusion of glycerol is able to trigger nociceptive inputs as evidenced by the occurrence of abdominal constrictions. This work was designed to evaluate the influence of 5-HT3 receptor antagonists on this reflex and to approach the site of action by comparing their relative efficacies according to the route of administration. Male Wistar rats (250-350 g) were surgically prepared for abdominal electromyography and a catheter was placed in the colonic lumen. Five days after surgery, electrical activity of abdominal muscles was recorded before and during (20 min) intracolonic infusion of glycerol (60% glycerol + 40% saline, rate 0.75 mL/h). Cilansetron was administered intraperitoneally, 15 min before glycerol infusion, at doses of 5 to 500 micrograms/kg. Granisetron, ondansetron and cilansetron were administered at the dose of 20 micrograms/kg by intraperitoneal (i.p.), intravenous (i.v.) or intracolonic (i.c.) routes. The number of abdominal spike bursts was used as an index of visceral nociception. Intracolonic infusion of glycerol increased significantly (P < 0.05) the number of abdominal spike bursts during the time of infusion compared with saline (30.6 +/- 6.6 vs 4.5 +/- 3.4 bursts). When administered i.p., cilansetron dose-dependently reduced the frequency of abdominal spike bursts from the dose of 20 micrograms/kg i.p. Administration i.p. of granisetron and ondansetron at this dose also significantly reduced the number of abdominal spikes (19.0 +/- 6.0 and 18.3 +/- 6.9 respectively). Cilansetron, ondansetron and granisetron were also effective by i.v. and i.c. routes, cilansetron was more active by the i.c. route. Serotonin, via 5-HT3 receptors, is involved in the mediation of abdominal contractions induced by intracolonic infusion of glycerol. 5-HT3 receptor antagonists are also active by i.c. route suggesting a local site of action.

Functional gut disorders: from motility to sensitivity disorders. A review of current and investigational drugs for their management

Functional gut disorders include several clinical entities defined on the basis of symptom patterns (e.g., functional dyspepsia, irritable bowel syndrome, functional abdominal pain, functional abdominal bloating), for which there is no established pathophysiological mechanism. Because there is no well-defined pathophysiological target, treatment should be aimed at symptom improvement. Prokinetics and antispasmodics have been widely used in the treatment of functional gut disorders on the assumption that disordered motility is the underlying cause of symptoms, and symptom improvement is indeed achievable with these compounds in some, but not all, patients with features of hypo- or hypermotility, respectively. In the first part of this review, we cover the basic pharmacology and discuss the rationale for the clinical use of prokinetics and antispasmodics. On the other hand, in the past few years, the explosive growth in the research focusing on visceral sensitivity and visceral reflexes has suggested that at least some patients with functional gut disorders have altered visceral perception. Thus, the second part of the review covers these developments and focuses on studies addressing the issue of drugs modulating visceral sensitivity.

Excitation and inhibition via adenosine receptors of the twitch response to electrical stimulation in isolated guinea pig ileum

The effects of adenosine and its related compounds on the cholinergic twitch response were examined in electrically stimulated guinea pig ileum. Adenosine (3 x 10(-7)-10(-5) M) and an adenosine A1-receptor agonist N6-cyclohexyladenosine (CHA, 10(-8)-10(-6) M) suppressed the twitch. Conversely, the A2a-receptor agonist 2-[p-(2-carboxyethyl)phenethylamino]-5'-N- ethylcarboxamidoadenosine (CGS 21680, 10(-9)-10(-7) M) potentiated the twitch in half the preparations examined. The A1-antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX), which per se did not affect the twitch, recovered the attenuated twitch caused by CHA (10(-7) M) or adenosine (10(-6) M) and converted it into a potentiated twitch. These results suggest the presence of adenosine A1- and A2a-receptors coupled negatively and positively, respectively, to acetylcholine release in the preparation.

Effects of the adenosine A1-receptor antagonist on defecation, small intestinal propulsion and gastric emptying in rats

We examined the effects of 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) and (R)-7,8-dihydro-8-ethyl-2-(3-noradamantyl)-4-propyl-1H-imidazo[2,1 -i]purin- 5(4H)-one (KF20274), selective adenosine A1-receptor antagonists, on the gastrointestinal propulsion in rats, as compared with those of the laxative bisacodyl. DPCPX and KF20274 (p.o.) dose-dependently increased the fecal pellet output, whereas these drugs at the dose that increased defecation did not affect small intestinal propulsion or gastric emptying. Bisacodyl increased defecation and slowed gastric emptying without any influence on small intestinal propulsion. Bisacodyl, but not DPCPX or KF20274, induced diarrhea at the dose inducing defecation. The present results suggest that the adenosine A1-receptor antagonist selectively enhances the lower gastrointestinal propulsion, resulting in defecation without diarrhea.