Tetrahydrobiopterin deficiency induces gastroparesis in newborn mice

Abstract

Pyloric stenosis, the most common infant gastrointestinal disease, has no known etiology and clinically presents as abnormal gastric emptying with evidence of pyloric muscle hypertrophy. Whether abnormalities in gastric muscle contraction and/or relaxation have a role in this condition is poorly known, but gastroparesis is commonly observed in association with delayed gastric emptying in adults. Therefore, we evaluated the tetrahydrobiopterin (BH4)-deficient newborn mouse model of this disease (hph-1) and hypothesized that their gastric muscle properties are impaired, when compared with wild-type control animals. In vitro studies evaluating the age-dependent gastric fundus muscle contraction and relaxation potential were conducted. Compared with wild-type mice, the hph-1 stomach content/body weight ratio was significantly increased in newborn but not juvenile or adult animals, confirming abnormal gastric emptying. Gastric tissue neuronal nitric oxide synthase (nNOS) protein expression was upregulated in both newborn and adult hph-1 mice, but in the former there was evidence of enzyme uncoupling and higher tissue superoxide generation when compared with same age-matched animals. As opposed to the lack of strain differences in the U46619-induced force, the newborn hph-1 gastric muscle carbachol-induced contraction and nNOS-dependent relaxation were significantly reduced (P Ͻ 0.01). These group differences were not present in juvenile or adult mice. Preincubation with BH4 significantly enhanced the newborn hph-1, but not wild-type, gastric muscle contraction. In conclusion, changes compatible with gastroparesis are present in the newborn mouse model of pyloric stenosis. The role of BH4 deficiency and possibly associated gastroparesis in the pathogenesis of infantile pyloric stenosis warrants further investigation. pylorus; gastric emptying; nitric oxide INFANTILE HYPERTROPHIC PYLORIC stenosis (IHPS) is a relatively common condition of unknown etiology and pathogenesis. Infants with this condition seldom exhibit any abnormalities at birth. The gastric outlet obstruction develops at 2-12 wk of life, and the pyloric sphincter hypertrophy quickly resolves after pyloromyotomy, a surgical intervention involving the longitudinal incision of the circular muscle (23,27,28).IHPS has traditionally been seen as a condition resulting from failure of the pyloric sphincter muscle to relax, thus preventing adequate and rapid gastric emptying following a meal. Infants with IHPS have a lower plasma nitrate level when compared with age-matched controls, and, following pyloromyotomy, the nitrate concentration increases to values found in normal infants (17). The pyloric tissue neuronal nitric oxide synthase (nNOS) expression is reduced in subjects with IHPS (1). Given nNOS role in NO generation, this has been postulated to play a significant role in the muscle hypertrophy and reduced sphincter relaxation observed in this condition.Gastric motility is regulated through enteric nervous system activity and involves both excitatory cholin...

Infantile hypertrophic pyloric stenosis (IHPS): A study of its pathophysiology utilizing the newborn hph-1 mouse model of the disease

“…Lastly, we conducted age-dependent comparative studies to address the mechanism accounting for the transient nature of gastric content stasis in hph-1 mice. As we have previously reported, the stomach content/body weight ratio is no longer increased in adult hph-1 mice, when compared with wild-type control animals, indicating that aging normalizes the increased pyloric sphincter tone (47). The hph-1 mice are BH4 deficient from birth and thus expected to show increased pyloric sphincter tone in the immediate postnatal period.…”

“…The hph-1 newborn mouse is the most suitable animal model for the study of the IHPS pathobiology because these animals exhibit the transient manifestations of pyloric stenosis present in the human condition (1,47), except for lack of sex predilection and absent vomiting. However, rodents lack the vomiting reflex, and this precludes them from getting as malnourished and dehydrated as seen in human infants with this condition (12,43).…”

“…BH4 deficiency results in nNOS uncoupling, leading to an increase in tissue superoxide content and tissue NO deficiency (11,41,47). The increased pyloric tone of the newborn hph-1 mice has been attributed to the BH4-induced tissue NO deficiency (1), without any further consideration given to the potential role of ROS in the sphincter contraction.…”

Pantoprazole decreases gastroesophageal muscle tone in newborn rats via rho-kinase inhibition

“…The muscle contraction potential was evaluated in response to either carbachol, or electrical field stimulation (EFS). EFS-induced force measurements were obtained in the presence of N G -nitro-Larginine methyl ester (L-NAME; 10 Ϫ4 M), propranolol (10 Ϫ5 M), and phentolamine (10 Ϫ5 M) by using a commercially available stimulator (Cibertec, Madrid, Spain) as follows: 80 V stimulation, 0.5-ms pulses with 20-s trains of at a frequency of 5 Hz, as previously reported (31). Three stimulations obtained 10 min apart were employed and averaged to determine the EFS-induced force increase.…”

Metoclopramide does not increase gastric muscle contractility in newborn rats

“…The contraction potentials of the muscle strips were evaluated through carbachol and bethanechol dose-response curves and electrical field stimulation (EFS). EFS was employed as previously reported (34), using a commercially available stimulator (Cibertec, Madrid, Spain) as follows: 80-V stimulation, 0.5-ms pulses with 20-s trains of at a frequency of 5 Hz. Three stimulations obtained 10 min apart were employed and averaged to determine the EFS-induced force increase.…”