Gastric and pyloric sphincter muscle function and the developmental-dependent regulation of gastric content emptying in the rat

The Effect of Botulinum Toxin in Experimental Hypertrophic Pyloric Stenosis

Purpose: Infantile hypertrophic pyloric stenosis is the most common cause of gastric outlet obstruction in the first month of life. Botulinum toxin (BT) is a neurotoxin produced by clostridium botulinum, which causes paralysis in skeletal muscles. We aimed to evaluate the effectiveness of BT in the experimental pyloric stenosis model. Methods: The study protocol was approved by the Selcuk University Medical Faculty Ethics Committee (2017/20). We performed an experimental study using 32 Wistar-Albino newborn rats. Rats were divided randomly into four groups with six rats in both control (C), and L-nitro-arginine methyl ester hydrochloride group, and 10 rats in each sham (S), and BT group. 100 mg/kg per day L-NAME was applied to all groups intraperitoneally for 14 days from birth except control group. 0.2 mL saline and 20 U/kg BT was injected by surgery to S and BT groups, respectively, at 21 days from birth. After 35 days all rats were sacrificed and biopsies were performed from pyloric muscle for histopathological examination. The results were evaluated with the "one-way ANOVA" test. Results: Total and circular muscle thickness of the groups were compared. The total muscle thickness of the L-NAME group was significantly higher than the control group (P = .031). Comparing the circular muscle thickness of botox group (BTG) with control group (CG) and L-NAME GROUP (LNG), muscle thickness was significantly smaller (P < .001, P < .001). The total muscle thickness of BTG was significantly different between LNG (P < .001). Conclusions: Hypertrophy of pylor in an experimental model was reduced by BT injection in this study. We think that Botox injection through endoscopic or interventional radiological methods may be an alternative method for surgery.

Physiological and histopathological effects of electroporation pulse on stomach of rats

BACKGROUND

Irreversible electroporation (IRE) is an emerging tissue ablation technique with widespread potential, especially for cancer treatment. Although the safety and efficacy of IRE for gastric tissue ablation have been demonstrated, there is a gap of knowledge regarding the effect of electroporation pulse (EP) on the physiology and histopathology of the stomach. This study applied EP to the stomach of healthy rats and investigated the digestive function, serum marker levels, and gastric tissue structure of EP-treated rats.

METHODS

Ninety male rats were divided into nine groups and examined up to 28 days post-treatment. A single burst of electroporation pulse (500 V, 99 pluses, 1 Hz, 100 µs) was delivered to the stomachs of rats using a tweezer-style round electrode. Gastric emptying, small intestinal transit, and gastric secretion were measured to evaluate the digestive function. Serum marker levels were determined using ELISA. Haematoxylin-eosin, Masson trichrome, and immunofluorescence were performed for histopathological analysis.

RESULTS

No  significant effect on gastric emptying or secretion was found post-EP, whereas the small intestinal transit decreased at 4 h and rapidly recovered to normal on 1-day post-EP. Further, serum TNF-α and IL-1β levels temporarily changed during the acute phase but returned to baseline within 28 days. Moreover, histopathological analysis revealed that cell death occurred immediately post-EP in the ablation area, whereas the gastric wall scaffold in the ablation region remained intact post-EP.

CONCLUSIONS

This study demonstrates the safety and efficacy of EP on the physiology and histopathology of the stomach and lays a foundation for more comprehensive applications of this technique.

Evolution of nitric oxide regulation of gut function

Although morphologies are diverse, the common pattern in bilaterians is for passage of food in the gut to be controlled by nerves and endodermally derived neuron-like cells. In vertebrates, nitric oxide (NO) derived from enteric nerves controls relaxation of the pyloric sphincter. Here, we show that in the larvae of sea urchins, there are endoderm-derived neuronal nitric oxide synthase (nNOS)-positive cells expressing pan-neural marker, Synaptotagmin-B (SynB), in sphincters and that NO regulates the relaxation of the pyloric sphincter. Our results indicate that NO-dependent pylorus regulation is a shared feature within the deuterostomes, and we speculate that it was a characteristic of stem deuterostomes.

Hydrogen peroxide promotes gastric motility in the newborn rat

BACKGROUND

When compared with infant formula, human milk enhances gastric emptying in preterm infants. Hydrogen peroxide (H₂O₂) is present in large quantities in human milk that has an antimicrobial role for the mother and infant. In vitro adult rat studies suggest that H₂O₂ facilitates gastric motor contraction. Hypothesizing that H₂O₂ enhances gastric motility, we investigated its effects on the newborn rat stomach tissue.

METHODS

Rat newborn and adult gastric fundic segments, or their smooth muscle cells, were used to evaluate the muscle response to H₂O₂ exposure. Tissue expression of Rho kinase 2 (ROCK-2; Western blot), its catalase activity, and H₂O₂ content (Amplex Red) were measured. H₂O₂ gastric mucosal diffusion was evaluated with Ussing chambers.

RESULTS

In both newborn and adult rats, H₂O₂ induced gastric muscle contraction and this response was attenuated by pre-incubation with the antioxidant melatonin. H₂O₂ passively diffused across the gastric mucosa. Its effect on the muscle was modulated via ROCK-2 activation and inhibited by melatonin.

CONCLUSION

H₂O₂, at a concentration similar to that of human milk, promotes gastric motility in the rat. To the extent that the present findings can be clinically extrapolated, the human milk H₂O₂ content may enhance gastric emptying in neonates.

The newborn rat gastric emptying rate is volume and not developmentally dependent

BACKGROUND

Gastric residuals are a common finding in enterally fed preterm neonates and traditionally thought to reflect immaturity-related delayed gastric emptying. Adult human data suggest that the meal volume regulate the gastric emptying rate, but early in life, this has not been adequately evaluated. The goal of this study was to study the rat postnatal changes in gastric emptying rate and the strain-induced effect on muscle contraction. We hypothesized that the stomach content volume and not developmental factors determines the newborn gastric emptying rate, via the Rho-kinase 2 (ROCK-2) pathway.

METHODS

Gastric volume and emptying rate measurements were obtained by ultrasound at different postprandial times and the wall strain-dependent changes in muscle contraction were evaluated ex vivo.

KEY RESULTS

The newborn rat gastric emptying rate was unrelated to postnatal age, maximal 30 min postprandial, and directly proportional to content volume. In vitro measurements showed that the agonist-induced gastric muscle contraction was directly proportional to the stomach wall strain. These changes were mediated via upregulation of ROCK-2 activity.

CONCLUSIONS & INFERENCES

The newborn rat gastric emptying rate is not developmentally regulated, but dependent on the content volume via wall strain-induced ROCK-2 activation. Further clinical studies addressing the content volume effect on the rate of gastric emptying are warranted, to enhance feeding tolerance in preterm neonates.