Hypertonicity of intestinal smooth muscle as a factor of intestinal ischemia in necrotizing enterocolitis

Gut transit time, using radiological contrast imaging, to predict early signs of necrotizing enterocolitis

BACKGROUND

Immature gut motility in preterm neonates may be a risk factor for necrotizing enterocolitis (NEC). Using preterm pigs as a model for infants, we hypothesized that intestinal dysmotility precedes NEC development.

METHODS

Eighty-five preterm pigs were fed increasing amounts of milk diets to induce NEC lesions, as detected at autopsy on day 5. Gut transit time was determined on day 4 by x-ray imaging after oral intake of contrast solution.

RESULTS

No clinical or radiological signs of NEC were detected on day 4, but macroscopic NEC lesions were recorded in 59% of pigs (n = 50) on day 5. Relative to pigs without NEC (noNEC, n = 35), pigs with small intestinal lesions (siNEC, n = 18) showed delayed stomach emptying time (StEmpty) and time for contrast to reach cecum (ToCecum) already on day 4. Pigs with lesions only in colon (coNEC, n = 20) showed more diarrhea, shorter ToCecum time, but longer small intestinal emptying time (SiEmpty). ToCecum time predicted siNEC and coNEC lesions with a receiver-operator characteristic area under the curve of 78-81%.

CONCLUSIONS

Region-dependent changes in gut transit time is associated with early NEC development in preterm pigs. How gut dysmotility is related to NEC in preterm infants requires further investigations.

IMPACT

Using preterm pigs as a model for preterm infants, we show that gut transit time, using serial x-ray contrast imaging, was changed in individuals with NEC-like lesions before they showed the typical radiological signs of NEC. Thus prolonged transit time across the entire gut was recorded when NEC lesions appeared in the small intestine but not when lesions were detected only in the colon. Until now, recordings of food transit have mainly investigated changes in the upper gut. Using serial x-rays, this study describes food transit across the entire gut and documents a region-dependent effect of NEC lesions on gut transit changes in preterm individuals. The findings provide proof of concept for use of x-ray contrast imaging as a tool to monitor gut transit in preterm pigs as models for infants. Delayed passage across the entire gut may be an early sign of small intestinal NEC, at least in pigs. More studies are needed to confirm relations in infants. In the future, it might be possible to use x-ray contrast imaging in preterm infants to better understand gut motility in relation to early NEC progression and need for medical NEC treatment.

Vasoactive intestinal polypeptide causes relaxation of the pyloric sphincter in the rabbit

Vasoactive intestinal peptide (VIP), which causes relaxation of gastrointestinal smooth muscle, has been found in high concentrations in the pylorus in many animal species, suggesting a prominent role for VIP in the control of pyloric sphincter function. We infused VIP into the gastric artery of 6 rabbits at rates from 12 to 1,200 ng/min and measured the intensity, duration, and frequency of spontaneous pyloric contractions with an intraluminal balloon and electromyography. VIP produced a dose-dependent reduction in the intensity (55% +/- 15% of baseline, P < .001) and the duration (29% +/- 25%, P < .001) of pyloric contraction. Maximal inhibition was observed at an infusion rate of 240 ng/min. The frequency of contractions did not decrease significantly in response to VIP infusion. Neostigmine infusion increased the intensity of pyloric contraction in a dose-dependent manner in doses of 0.10, 0.15, and 0.25 mg (140% +/- 78%, 273% +/- 76%, and 357% +/- 26% of baseline, respectively; P < .001). VIP infusion at 12 ng/min and 480 ng/min completely inhibited the increased intensity of contraction at neostigmine doses of 0.10 and 0.15 mg, respectively. Our results show that VIP decreases the intensity and the duration of pyloric contraction in a dose-dependent manner. As pyloric spasm may contribute to the pathogenesis of hypertrophic pyloric stenosis, we can postulate a role for reduced VIP-induced relaxation in the pathophysiology of hypertrophic pyloric stenosis.

Indium 111 oxine-labeled leukocytes for early diagnosis of ischemic enterocolitis

The feasibility of the use of indium 111 oxine-labeled autologous leukocytes for the diagnosis of ischemic enterocolitis in vivo was examined in an experimental model of ischemia in dogs. A 30-cm segment of small intestine was devascularized by ligating the arteries and veins from the last arcade in 7 dogs. A sham operation was performed in 3 control dogs. 111In oxine-labeled autologous white blood cells were infused 3.5 hours after operation. Anterior and lateral nuclear scanning was performed at 6 and 24 hours postinfusion with a gamma camera equipped with a low-energy magnifying multihole collimator. The animals were killed after 24 hours. The gross and microscopic appearance of the bowel was evaluated. The radioactivity in the serial specimens of the bowel was measured. In vivo scans were positive (ie, increased uptake in the bowel loop) in all dogs with intestinal ischemia at 6 and 24 hours. No significant uptake was noted in control dogs. Rectilinear scan of the bowel removed at autopsy showed a correlation between the area of infarction and tracer accumulation. In addition, there was a progressive decrease in uptake of 111In oxine from the center of the ischemic lesions to the periphery. Forty percent of the total radioactivity was measured at the center of the lesion, whereas only 6.5% was present at 22.5 cm from the center. Thus the ratio between the ischemic and normal tissue was 10:1 (range, 6.5 to 16). These studies demonstrate that 111In oxine-labeled autologous white blood cells can be used for the diagnosis of ischemic enterocolitis.(ABSTRACT TRUNCATED AT 250 WORDS)

Vasoactive intestinal polypeptide potentiates the hypoxemia-induced decrease in splanchnic circulation in the rat

The effects of acute infusion of vasoactive intestinal polypeptide (VIP) and hypoxemia on splanchnic circulation were examined in 35 awake Sprague-Dawley rats. Indwelling catheters were placed in the superior vena cava and the proximal aorta via the internal jugular vein and internal carotid artery, respectively, while the rats were under ether anesthesia. Four hours later, when the rats were awake and active, VIP (molecular lot 3226) was infused intraarterially for 30 minutes. The distribution of cardiac output was measured at the end of VIP infusion using 125I-labeled microspheres. VIP was administered at a low (1.5 ng/min) and a high infusion rate (44.1 ng/min) for 30 minutes. The effect of hypoxemia on circulatory response to VIP was examined only in the high VIP infusion group, by placing the rat in a 10% oxygen environment. Appropriate control experiments were performed with each group. The high-dose VIP resulted in a marked reduction in distribution of cardiac output to the splanchnic circulation. This effect was potentiated by hypoxemia, particularly in the distal ileum and colon. The metabolic clearance rate of VIP increased with the rate of VIP infusion and was decreased by hypoxemia. It was concluded that only in high concentration does VIP have any effect on splanchnic circulation. However, in the presence of hypoxemia, VIP may have an important role in cardiovascular compensatory response and may contribute to the development of ischemic bowel injury.