Umbilical arterial blood flow in the mouse embryo during development and following acutely increased heart rate

Abstract

In anesthetized, pregnant ICR mice, we measured embryonic umbilical arterial velocity at baseline and during bipolar atrial or ventricular pacing. Pregnant mice were anesthetized with pentobarbital (60 mg/kg intraperitoneal) and ventilation was mechanically supported via a tracheotomy. Embryos were exposed through a mid-line laparotomy and regional hysterotomy. We recorded umbilical velocity using a 1-mm diameter piezoelectric crystal and 20-MHz, pulsed Doppler velocimeter at embryo day (ED) 10.5 ( n = 8), 12.5 ( n = 10), 13.5 ( n = 27), 14.5 ( n = 12), and 16.5 ( n = 17). We then acutely altered embryonic heart rate in n = 8 ED 13.5 mouse embryos by bipolar atrial and ventricular pacing. Embryonic heart rate in this experimental preparation increased from 123 ± 7 to 193 ± 11 beats/min from ED 10.5 to 16.5 ( p < 0.05). Peak instantaneous average velocity increased from 21 ± 2 to 55 ± 6 mm/s from ED 10.5 to 16.6 ( p < 0.05), as did stroke volume and blood flow ( p < 0.05 for each). In contrast to human umbilical arterial velocity profiles, significant forward diastolic flow was not seen at these stages, suggesting higher placental resistance in mice versus humans at comparable developmental time points. As previously noted for the chick embryo, murine embryonic umbilical arterial velocity decreased after atrial pacing and disappeared after ventricular pacing. Thus, we can determine embryonic umbilical blood flow during the overlapping periods of murine cardiac and placental morphogenesis.