In Vivo Assessment of Embryonic Cardiovascular Dimensions and Function in Day-10.5 to -14.5 Mouse Embryos

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Abstract
Embryonic cardiovascular function has been extensively studied in vivo in the chick embryo. However, the geometry of mammalian and avian hearts differs; the mammalian cardiovascular system is coupled to both yolk sac and placental circulations, and unique murine genetic models associated with structural and functional cardiovascular defects are now available. We therefore adapted techniques validated for the chick embryo to define cardiovascular dimensions and function in the mouse embryo. We bred C3HeB female and C57Bl/J6 male mice and ICR pairs for experiments on embryonic days (EDs) 10.5 to 14.5 (n=130 dams). After maternal anesthesia (pentobarbital, 60 mg/kg IP), laparotomy, and sequential regional hysterotomy, we exposed and then imaged individual embryos at 60 Hz (video) in the ventral and/or left anterior oblique views while maintaining uteroplacental continuity. We measured epicardial chamber dimensions and then calculated right and left ventricular elliptical volumes from areas. In addition, we measured pulsed-Doppler blood velocity across the atrioventricular cushions and ventricular outflow tract. We maintained embryonic temperature with a heated surgical platform, topical oxygenated and warmed buffer, and warming lamps. Embryonic heart rate increased from 124.7±5.2 to 194.3±13.2 bpm from EDs 10.5 to 14.5 (P<.01). Right and left ventricular end-diastolic and end-systolic dimensions increased (P<.05 by ANOVA for each). Maximal ventricular mean inflow and outflow velocities increased from 62.33±4.06 to 106.23±11.59 and from 55.79±6.11 to 91.61±6.93 mm/s, respectively (P<.05 by ANOVA for each). Thus, as has been done for chick and rat embryos, the maturation of murine embryonic cardiovascular function can be quantified in vivo, setting the stage for the investigation of structure-function relations in mouse models of cardiovascular development and disease.