Why the enteric nervous system is important to clinicians

Prenatal intestinal obstruction affects the myenteric plexus and causes functional bowel impairment in fetal rat experimental model of intestinal atresia

Background

Intestinal atresia is a rare congenital disorder with an incidence of 3/10 000 birth. About one-third of patients have severe intestinal dysfunction after surgical repair. We examined whether prenatal gastrointestinal obstruction might effect on the myenteric plexus and account for subsequent functional disorders.

Methodology/Principal Findings

We studied a rat model of surgically induced antenatal atresia, comparing intestinal samples from both sides of the obstruction and with healthy rat pups controls. Whole-mount preparations of the myenteric plexus were stained for choline acetyltransferase (ChAT) and nitric oxide synthase (nNOS). Quantitative reverse transcription PCR was used to analyze mRNAs for inflammatory markers. Functional motility and permeability analyses were performed in vitro. Phenotypic studies were also performed in 8 newborns with intestinal atresia. In the experimental model, the proportion of nNOS-immunoreactive neurons was similar in proximal and distal segments (6.7±4.6% vs 5.6±4.2%, p = 0.25), but proximal segments contained a higher proportion of ChAT-immunoreactive neurons (13.2±6.2% vs 7.5±4.3%, p = 0.005). Phenotypic changes were associated with a 100-fold lower concentration-dependent contractile response to carbachol and a 1.6-fold higher EFS-induced contractile response in proximal compared to distal segments. Transcellular (p = 0.002) but not paracellular permeability was increased. Comparison with controls showed that modifications involved not only proximal but also distal segments. Phenotypic studies in human atresia confirmed the changes in ChAT expression.

Conclusion

Experimental atresia in fetal rat induces differential myenteric plexus phenotypical as well as functional changes (motility and permeability) between the two sides of the obstruction. Delineating these changes might help to identify markers predictive of motility dysfunction and to define guidelines for post-surgical care.

An inherent acceleratory effect of insulin on small intestinal transit and its pharmacological characterization in normal mice

AIM: To study an inherent effect of insulin on small intestinal transit and to explore involvement of various systems/mechanisms in normal mice.

METHODS: Insulin at the doses of 2 μU/kg, 2 mU/kg, 2 U/kg or vehicle was subcutaneously administered to four groups of overnight fasted normal male mice. Blood glucose (BG) levels were measured 2 min before insulin administration and 2 min before sacrificing the animals for the measurement of small intestinal transit (SIT). Charcoal meal was administered (0.3 mL) intragastrically 20 min after insulin administration and animals were sacrificed after 20 min and SIT was determined. For exploration of the various mechanisms involved in insulin-induced effect on SIT, the dose of insulin which can produce a significant acceleration of SIT without altering BG levels was determined. The following drugs, atropine (1 mg/kg), clonidine (0.1 mg/kg), ondansetron (1 mg/kg), naloxone (5 mg/kg), verapamil (8 mg/kg) and glibenclamide (10 mg/kg), were administered intravenously 10 min prior to the administration of insulin (2 μU/kg).

RESULTS: The lower doses of insulin (2 μU/kg and 2 mU/kg) produced a significant acceleration of SIT from 52.0% to 70.7% and 73.5% without lowering blood glucose levels (P < 0.01), while the highest dose of insulin (2 U/kg) produced a fall in blood glucose levels which was also associated with significant acceleration of SIT (P < 0.01). After pretreatment of insulin (2 μU/kg) group with atropine, insulin could reverse 50% of the inhibition produced by atropine. In clonidine-pretreated group, insulin administration could reverse only 37% of the inhibition produced by clonidine and inhibition of SIT was significant compared with vehicle + insulin-treated group, i.e. from 74.7% to 27.7% (P < 0.01). In ondansetron-pretreated group, insulin administration could produce only mild acceleration of SIT (23.5%). In naloxone-pretreated group, insulin administration could significantly reverse the inhibition of SIT produced by naloxone when compared with naloxone per se group, i.e. from 32.3% to 53.9% (P < 0.01). In verapamil-pretreated group, insulin administration could only partially reverse the inhibition (65%). In glibenclamide-pretreated group, insulin administration produced further acceleration of SIT (12.2%).

CONCLUSION: Insulin inherently possesses an acceleratory effect on SIT in normal mice. Adrenergic and cholinergic systems can play a significant role. Calcium channels and opioidergic system can play a supportive role; in addition, enhancement of endogenous insulin release can augment the effect of exogenously administered insulin on SIT.