José Ronaldo Vasconcelos da Graça

Sildenafil, a phosphodiesterase-5 inhibitor, delays gastric emptying and gastrointestinal transit of liquid in awake rats.

We studied the effect of sildenafil on gastric emptying (GE) and gastrointestinal (GI) transit in awake rats. After cervical vessel cannulation and 24 hr of fasting, the animals received an intravenous (IV) injection of sildenafil (4 mg/kg) or vehicle. Next they were gavage fed (1.5 ml) with a test meal (phenol red in 5% glucose solution, 0.5 mg/ml) and sacrificed 10, 20, or 30 min later. Experimental and control subsets consisted of 5–10 rats. Gastric and proximal, medial, and distal small intestine dye retentions (GDR and IDR, respectively) were obtained by spectrophotometry. Data were compared by ANOVA and Student-Newman-Keuls test. In sildenafil-treated animals, GDR increased (P < 0.05) by 20.3%, 46.9%, and 55,5% while medial IDR decreased (P < 0.05) by 35.1%, 43.4%, and 41.6%, respectively, at 10, 20, and 30-min intervals. Proximal and distal IDR values did not change in sildenafil-treated animals. Mean arterial pressure (MAP) decreased 25% (P < 0.05) right after sildenafil administration but normalized afterwards while in controls MAP remained unchanged. In conclusion, sildenafil delays GE and GI transit of a liquid meal while transiently decreases MAP in awake rats.

Heme oxygenase/carbon monoxide-biliverdin pathway may be involved in the antinociceptive activity of etoricoxib, a selective COX-2 inhibitor

The aim of this study was to assess the interaction between the heme oxygenase-1/ biliverdin/carbon monoxide (HO-1/BVD/CO) and cyclooxygenase-2 (COX-2) pathways in the writhing test. Mice were pretreated with 0.1, 1 or 10 mg/kg, ip etoricoxib, a selective COX-2 inhibitor, or with one of the following HO-1/BVD/CO pathway modulators: 1, 3 or 9 mg/kg, sc ZnPP IX, a specific HO-1 inhibitor, 0.3, 1 or 3 mg/kg, sc hemin, a substrate of the HO-1/BVD/CO pathway; or 0.00025, 0.025 or 2.5 μmol/kg, sc DMDC, a CO donor. Mice pretreated with etoricoxib or one of the HO-1/BVD/CO pathway modulators received an injection of acetic acid (ip) after 30 and 60 min, respectively. Next, the number of writhes was quantified between 0 and 30 min after stimulus injection. In another series of experiments, ineffective doses of etoricoxib were co-administered with hemin or DMDC and an effective dose of etoricoxib with ZnPP IX, followed by an acetic acid injection. Four hours after the acetic acid injection, levels of bilirubin, which is a product of BVD conversion by the BVD reductase enzyme, in the peritoneal lavage were determined. Hemin or DMDC reduced (p<0.05) the number of writhes, but ZnPP IX potentiated (p<0.05) the effect of acetic acid by increasing (p < 0.05) the number of writhes. The co-administration of etoricoxib with hemin or DMDC reduced (p<0.05) the number of writhes. However, the analgesic effect of etoricoxib was not observed in the presence of ZnPP IX. Pretreatment with ZnPP IX reduced bilirubin levels, but etoricoxib pretreatment significantly increased the bilirubin concentration in peritoneal exudates. The data obtained from these experiments showed that the HO-1/BVD/CO pathway was activated in the acetic acid-induced abdominal writhing model. The analgesic effect of etoricoxib was at least partially dependent on the participation of the HO-1/BVD/CO pathway.

A plethysmometric method for gastric compliance studies in anesthetized rats

A new method to study gastric volume by plethysmography is presented. Twenty male Wistar rats (250-300 g) were fasted for 24 h. After anesthesia with urethane (1.2 g/kg, i.p.), a tracheostomy was performed, and cervical vessels were cannulated. A balloon catheter was introduced per os and positioned in the proximal stomach. The opposite end of the catheter was connected to a reservoir (volume = 30 ml; inside diameter = 2.5 cm), coupled to a plethysmometer. A standard ionic solution was used to fill the balloon ( approximately 3.0 ml) and the communicating vessel system. Calibration experiments (n = 5) displayed a strong (r(2) = 0.99) correlation between graded balloon-volume changes and plethysmometric recordings. Because distending pressure of the stomach remained constant, the balloon-volume recordings were taken as gastric compliance index. Gastric volume changes, mean arterial pressure, and heart rate of animals of control and experimental groups were monitored for 90 min. The data were analyzed by analysis of variance and the Student-Newman-Keuls test. In control animals (n = 5), no significant changes on gastric volume and hemodynamic values were found. Experimental animals were treated with either yohimbine (n = 5) or bethanechol (n = 5) i.v. injections. The rats received consecutive doses of yohimbine (0.5 and 1 mg/kg) or bethanechol (1.5 and 3 microg/kg), 30 min apart. Both doses of each treatment transiently induced hypotension and bradycardia (p < 0.05). Yohimbine treatment (1 mg/kg) increased gastric volume by half (p < 0.05), whereas bethanechol (3 microg/kg) decreased it by 35% (p < 0.05). In summary, this work shows a suitable method to directly assess gastric compliance in anesthetized rats.

Variations in gastric emptying of liquid elicited by acute blood volume changes in awake rats

We have observed that acute blood volume expansion increases the gastroduodenal resistance to the flow of liquid in anesthetized dogs, while retraction decreases it (Santos et al. (1991) Acta Physiologica Scandinavica, 143: 261-269). This study evaluates the effect of blood volume expansion and retraction on the gastric emptying of liquid in awake rats using a modification of the technique of Scarpignato (1980) (Archives Internationales de Pharmacodynamie et de Therapie, 246: 286-294). Male Wistar rats (180-200 g) were fasted for 16 h with water ad libitum and 1.5 ml of the test meal (0.5 mg/ml phenol red solution in 5% glucose) was delivered to the stomach immediately after random submission to one of the following protocols: 1) normovolemic control (N = 22), 2) expansion (N = 72) by intravenous infusion (1 ml/min) of Ringer-bicarbonate solution, volumes of 1, 2, 3 or 5% body weight, or 3) retraction (N = 22) by controlled bleeding (1.5 ml/100 g). Gastric emptying of liquid was inhibited by 19-51.2% (P < 0.05) after blood volume expansion (volumes of 1, 2, 3 or 5% body weight). Blood volume expansion produced a sustained increase in central venous pressure while mean arterial pressure was transiently increased during expansion (P < 0.05). Blood volume retraction increased gastric emptying by 28.5-49.9% (P < 0.05) and decreased central venous pressure and mean arterial pressure (P < 0.05). Infusion of the shed blood 10 min after bleeding reversed the effect of retraction on gastric emptying. These findings suggest that gastric emptying of liquid is subject to modulation by the blood volume.

Spinal cord transection modifies ileal fluid and electrolyte transport in rats.

Spinal cord injury (SCI) is associated with severe autonomic changes, including inhibition of gastrointestinal (GI) motility. GI motility changes are known to affect electrolytes transport and these changes have not been adequately studied after SCI. We studied the ileal permeability to fluid and electrolytes in rats submitted to experimental spinal cord transection (SCT), between T4 and T5, throughout the first week after SCT. SCT increased ileal secretion of Na+ (P<0.05) and decreased the Cl(-) absorption during the first week post SCI (P<0.05). Water transport was also significantly altered, leading to increased water secretion following the Na+ gradient. Ileal secretion of K+ was significantly increased 1 and 7 days after spinal cord injury. To our knowledge, the present findings are the first direct evidence that SCT alters ileal electrolyte transport in rats. Further studies are necessary to evaluate the mechanisms involved in this phenomenon.

Inhibitory effect of sildenafil on rat duodenal contractility in vitro: putative cGMP involvement.

1. Sildenafil citrate (Viagra™; Pfizer, Sandwich, Kent, UK), a phosphodiesterase 5 inhibitor, rises cGMP levels in smooth muscle cells. It relaxes both vascular and visceral smooth muscle. In order to assess the intestinal effects of sildenafil, we decided to investigate its actions on rat duodenal motor activity in vitro.

Gastroduodenal resistance and neural mechanisms involved in saline flow decrease elicited by acute blood volume expansion in anesthetized rats.

We have previously demonstrated that blood volume (BV) expansion decreases saline flow through the gastroduodenal (GD) segment in anesthetized rats (Xavier-Neto J, dos Santos AA & Rola FH (1990) Gut, 31: 1006-1010). The present study attempts to identify the site(s) of resistance and neural mechanisms involved in this phenomenon. Male Wistar rats (N = 97, 200-300 g) were surgically manipulated to create four gut circuits: GD, gastric, pyloric and duodenal. These circuits were perfused under barostatically controlled pressure (4 cmH2O). Steady-state changes in flow were taken to reflect modifications in circuit resistances during three periods of time: normovolemic control (20 min), expansion (10-15 min), and expanded (30 min). Perfusion flow rates did not change in normovolemic control animals over a period of 60 min. BV expansion (Ringer bicarbonate, 1 ml/min up to 5% body weight) significantly (P < 0.05) reduced perfusion flow in the GD (10.3 +/- 0.5 to 7.6 +/- 0.6 ml/min), pyloric (9.0 +/- 0.6 to 5.6 +/- 1.2 ml/min) and duodenal (10.8 +/- 0.4 to 9.0 +/- 0.6 ml/min) circuits, but not in the gastric circuit (11.9 +/- 0.4 to 10.4 +/- 0.6 ml/min). Prazosin (1 mg/kg) and yohimbine (3 mg/kg) prevented the expansion effect on the duodenal but not on the pyloric circuit. Bilateral cervical vagotomy prevented the expansion effect on the pylorus during the expansion but not during the expanded period and had no effect on the duodenum. Atropine (0.5 mg/kg), hexamethonium (10 mg/kg) and propranolol (2 mg/kg) were ineffective on both circuits. These results indicate that 1) BV expansion increases the GD resistance to liquid flow, 2) pylorus and duodenum are important sites of resistance, and, 3) yohimbine and prazosin prevented the increase in duodenal resistance and vagotomy prevented it partially in the pylorus.

Atrial stretch delays gastric emptying of liquids in awake rats.

AIMS We previously reported that mechanical atrial stretch (AS) by balloon distention increased gastric tonus in anesthetized rats. The present study evaluated the effect of AS on the gastric emptying of a liquid test meal in awake rats and its underlying neural mechanisms. MAIN METHODS Anesthetized male rats received a balloon catheter into the right atrium and a gastrostomy cannula. The next day, mean arterial pressure (MAP), heart rate (HR), central venous pressure (CVP), and cardiac output (CO) were continuously monitored. After the first 20min of monitoring (basal interval), the balloon was either distended or not (control) with 30, 50, or 70μl saline for 5min. Fifteen minutes later, the rats received the test meal (glucose solution with phenol red), and fractional gastric dye retention was determined 10, 20, or 30min later. KEY FINDINGS Heart rate and CVP values were transiently increased by 50 or 70μl AS but not 30μl AS, whereas gastric emptying was slower after 30, 50, or 70μl AS than after sham distention. Subdiaphragmatic vagotomy or splanchnicotomy+celiac ganglionectomy and capsaicin, ondansetron, hexamethonium, L-NAME, and glibenclamide treatment prevented the AS-induced delay in gastric emptying, whereas atropine and guanethidine treatment failed to prevent it. SIGNIFICANCE Atrial stretch inhibited the gastric emptying of liquid via non-adrenergic and non-cholinergic pathways that activate nitric oxide-K(+)ATP channels.

1.8 cineole decreases gastric compliance in anesthetized rats

PURPOSE To study the effect of 1,8 cineole components of the essential oil of Croton nepetaefolius--plant of North-East of Brasil, used in the popular medicine for riots of the gastrointestinal tract--on the motor behavior of the gut of Wistar rats. METHODS Used 16 male animals under jejun of 24h weighing 300-350 g. The effect of 1.8 cineole (1 or 3mg/Kg) on gastric compliance had been lead in anaesthetized rats. The variations of the gastric volume (GV), had been measured by plethysmography, while AP, HR and CVP had been monitored continuously by a digital system of data acquisition. RESULTS Observe reduction of the GV, which was significant on 30, 40, 50 and 60 min after treatment (2.0 +/- 0.1; 1.9 +/- 0.1; 1.8 +/- 0.1 and 1.7 +/- 0.1mL, versus 2.1 +/- 0.2mL). The AP presented significant fall after the administration of 1.8 cineole, remaining thus during 60min of monitorization (87.9 +/- 7.7; 87.6 +/- 7.1; 87.9 +/- 6.4; 87.8 +/- 5.7; 86.0 +/- 5.5 and 87.7 +/- 6.0mmHg, respectively versus 94.4 +/- 6.2 mmHg), as well as the HR (366.3 +/- 13.4; 361.7 +/- 11.5; 357.3 +/- 10.4; 353.0 +/- 10.4; 348.3 +/- 11.1 and 350.4 +/- 13.7bpm, respectively versus 395.2 +/- 11.1bpm). The CVP did not suffer significant variations after treatment. CONCLUSION Observe the 1.8 cineole reduces the gastric compliance in anaesthetized rats besides presenting effect hypotensor and bradycardia; probably for direct action on the gastrointestinal and vascular smooth muscle and moduling the autonomic nervous system.

Effect of a crude sulfated polysaccharide from Halymenia floresia (Rhodophyta) on gastrointestinal smooth muscle contractility

The aim of this work was to study the effect of Halymenia floresia (Hf) on duodenum contractility, and on experimental protocols of gastric compliance (GC) in rats. Fraction Hf2s exhibited a concentration-dependent myocontractile effect (EC50 12.48 µg/ml), and an inhibitory effect after consecutive washing. The contractile response promoted by Hf2s in the duodenum strips was completely inhibited by verapamil, and the effects were prevented in the presence of Ca2+-free medium. The pretreatment with atropine prevented the Hf2s myocontractile effect. Hf2s was also capable to decrease the GC (from 3.8±0.06 to 3.4±0.13 ml, P<0.05), which did not return to basal levels after more 50 min of observation. These results indicated that the algal polysaccharide possessed in vitro and in vivo gastrointestinal effects.