Effect of ischemic anoxia on electrical and mechanical activity of the totally isolated porcine stomach

Does maternal nicotine exposure during gestation increase the injury severity of small intestine in the newborn rats subjected to experimental necrotizing enterocolitis

BACKGROUND/PURPOSE

The aim of this study was to evaluate the effects of maternal nicotine exposure during gestation on injury severity of small intestine in the newborn rats subjected to hypoxia-reoxygenation and cold stress.

METHODS

A total of 21 Sprague-Dawley pregnant rats were divided into 3 equal groups. The groups were labeled as group 1, control group; group 2, hypoxia-reoxygenation group; and group 3, nicotine-hypoxia-reoxygenation group. The rats of group 3 were exposed to nicotine via subcuticular injection for the last week of gestation (2 mg/kg/d). Newborn rats were collected immediately after birth to prevent suckling of maternal milk (40 rat pups in group 1, 43 rat pups in group 2, and 41 rat pups in group 3). Litters in groups 2 and 3 were stressed twice daily with asphyxia followed by cold (4 degrees C for 10 minutes) stress to induce hypoxic intestinal injury which is relevant to human necrotizing enterocolitis. Breathing 100% CO2 for 10 minutes in a chamber followed by 10-minute 100% O2 breathing was the asphyxia model repeated twice daily. After hypoxia-reoxygenation and cold stress, newborn rats were returned to their mother's cages. This protocol was repeated for the following 2 days, and the rat pups were decapitated on the third day. Using this protocol of asphyxia and cold stress, all of neonatal rats developed clinical and pathological signs of hypoxia-induced intestinal injury. The entire gastrointestinal tract was removed and examined macroscopically. A 2-cm section of distal ileum from each animal was taken for histopathological and biochemical examinations. Histological changes in ileal architecture were scored and graded from 1 to 5. The remaining intestinal tissues of the animals were used for lipid peroxidation analysis.

RESULTS

Typical signs of hypoxia-induced intestinal injury were observed in the 2 experimental groups (groups 2 and 3) macroscopically. There were more grades 3 and 4 injuries in group 3 (P < .05). The malondialdehyde levels were elevated in groups 2 and 3 (P < .001). The malondialdehyde levels of the group 3 were also significantly higher than group 2 (P < .01).

CONCLUSIONS

Maternal nicotine exposure during gestation results in higher grade histological injury in newborn rats subjected to hypoxia-reoxygenation and cold stress.

Effect of hypoxia on fetal rabbit gastrointestinal motility

During fetal hypoxic stress, blood flow is shunted from nonvital to life-preserving organs, including the heart and brain. Reduced oxygen to the small intestine (SI) induces mucosal injury and may contribute to neonatal necrotizing enterocolitis (NEC). As little is known about the relationship between fetal hypoxia and GI motility, we assessed potential effects in a rabbit model. Twenty-one pregnant rabbits were randomized into two groups, hypoxia (Hyp) and control (Cont). Seven litters were studied at Gestational Days 24, 27, and 30 of their normal 31-day gestation. Under ultrasound guidance each fetal stomach was percutaneously accessed. Fluorescein, labeled with color-coded microspheres for precise fetal identification, was injected. Hyp rabbits breathed 11% oxygen for 1 h after recovery from anesthesia; Cont rabbits breathed room air. Two hours after injection, fetuses were delivered and weighed. The SI was harvested, the length recorded, and the distance fluorescein traveled measured by UV light optical density. Results were analyzed by the unpaired Student test. All injected fetuses (N = 167) survived. The length fluorescein traveled was shorter in Hyp than Cont at all gestational days studied (P < 0.01): Day 24, Hyp = 6.7 +/- 2.0 vs Cont = 8.4 +/- 2.1 cm; Day 27, Hyp = 10.1 +/- 2.9 vs Cont = 19.1 +/- 4.4 cm; and Day 30, Hyp = 16.8 +/- 3.5 vs Cont = 23.1 +/- 5.2 cm. The percentage motility, defined as the length of fluorescein travel divided by total SI length, was also significantly less at all gestational days. Fetal rabbit GI motility was significantly decreased by maternal hypoxia during the last third of gestation. Hypoxia-induced reduction in GI motility may contribute to neonatal NEC.

The effect of thermal injury on gastric emptying in rats

Gastric distension and gastrointestinal discomfort are common complications of burn injuries. This study was designed to examine the effect of thermal injury on the emptying rate of liquids in conscious rats fitted with stainless steel cannulae in the body of the stomach. In rats with partial-thickness burns emptying of the hyperosmolal saline was found to be delayed (P < 0.5) with respect to control only during the chronic phase of injury. However, full-thickness burns delayed hyperosmolal saline emptying in both acute and chronic phases, together with delayed saline emptying in the acute state. Thermal injury did not influence the gastric emptying of peptone and acid solutions, which activate different pathways to delay gastric emptying. Delayed gastric emptying of hyperosmolal solutions may be explained by increased sympathetic and opiatergic nervous activities, resulting in reflex relaxation of gastric smooth muscle.

Strenuous exercise decreases motility and cross-sectional area of human gastric antrum. A study using ultrasound

Gastric emptying in humans is delayed with strenuous exercise. We used ultrasound imaging in six healthy volunteers to determine whether changes in motility and configuration of the gastric outlet contribute to this delay. After fasting, all individuals ingested chicken broth and garbanzo beans. With subjects sitting upright, transverse and longitudinal real-time views of the gastric antrum were recorded on video tape. In the exercise studies, subjects pedaled an ergometer for 10 min to attain a heart rate of 85% predicted maximum. On a different day, all subjects had an identical study without exercise. The order of performance of exercise and no-exercise studies was randomized. After exercise, contraction frequencies and antral areas were significantly reduced compared to the studies without exercise. In addition, after exercise there was closure of the pylorus and tubular narrowing of the gastric antrum. Closure of the pylorus and decreased gastric antral area and motility may be important in explaining the decrease in gastric emptying that occurs with strenuous exercise.

The effect of cold-restraint stress on gastric emptying in rats

The effects of drug treatment and of cold-restraint stress (a method used to produce experimental stomach ulcers) on gastric emptying of a resin (colestipol-phenol red complex) were investigated in rats. Gastric emptying was decreased by intraperitoneal treatment with atropine (0.3 mg/kg) or verapamil (4 mg/kg), and enhanced by bethanechol (1.2 mg/kg). Stress by restraint at 4 degrees C for 2 hr markedly reduced gastric emptying; the pattern of effects of drug pretreatment in these stressed rats was similar to that seen in their nonstressed controls. Further experiments, with stress for 3 hr, revealed that the gastric emptying rate was triphasic; increasing in the first hr, returning to normal and then slowing in the third hr of stress. Initial increase in emptying rate was probably due to predominant vagal overactivity. Hypothermia and possibly other factors induced by cold-restraint stress could have subsequently depressed gastric motility.

Effect of hemorrhagic hypotension and hypoventilation on lower esophageal sphincter pressure

Dysfunction of the lower esophageal sphincter has been demonstrated in the cat shock model. Analogies have been drawn to reflux and aspiration in the critically ill patient. In a cat shock model, lower esophageal sphincter pressure is reduced and response to bethanechol is impaired. Upon resuscitation to basal state with heparinized shed blood, the lower esophageal basal pressure returns to normal values, and response to bethanechol is restored. This model may explain reflux and aspiration in the critically ill patient.