In Vivo Ultrasound Assessment of Gastric Emptying in Newborn Mice

ABSTRACT Objectives: The aim of the present study was to develop an ultrasonographic approach to comparatively assess gastric emptying in newborn wild‐type and guanosine triphosphate cyclohydrolase knockout hph‐1 mice, because we previously reported gastroparesis early in life in this strain. Methods: Stomach transverse, anteroposterior, and longitudinal ultrasonographic measurements were obtained with a 40‐MHz transducer in pups immediately after maternal separation and 4 hours later. A conventional equation was used and the predicted values validated by obtaining postmortem gastric content volume measurements. Wild‐type and hph‐1 mice gastric emptying rates were comparatively evaluated at 1 to 3 and 5 to 8 days of age, respectively. Results: The ultrasound equation closely predicted the newborn stomach content volumes with a correlation coefficient (R2) of 0.93 and 0.81 (P < 0.01) for measurements obtained on full stomach and after 4 hours of fasting, respectively. In wild‐type mice, gastric emptying was age dependent and associated with a greater residual volume at 1 to 3 days (65% ± 7%), as compared with 5‐ to 8‐day‐old pups (33% ± 4%; P < 0.01), after fasting. In contrast, an equal duration of fasting resulted in a significantly greater residual gastric content volume in 5‐ to 8‐day‐old hph‐1 mice (68% ± 7%; P < 0.01), as compared with same‐age wild‐type mice. Conclusions: Ultrasonography offers a sensitive and accurate estimate of gastric content volume in newborn mice. In wild‐type newborn mice, gastric emptying rate is age dependent and significantly reduced in the immediate postnatal period. The newborn hph‐1 mice have a significantly higher gastric residual volume, as compared with wild‐type same‐age animals.