LEFT-VENTRICULAR VOLUMES AND FUNCTION IN THE EMBRYONIC MOUSE HEART

This study describes miniaturized technology for the in vivo analysis of the volume and function of the embryonic mouse heart and the applic ation of this technology to study the normal embryonic left ventricle (LV) at two stages of development. With the use of microsurgical techn iques, embryos from embryonic clay (ED) 10.5 (ED10.5) to ED16 were del ivered individually from litters of normal dams, and cardiac visualiza tion was achieved with the use of intravital microscopy by transillumi nation, with the umbilical circulation intact. At ED10.5-11, the heart could be imaged in color in the intact embryo, whereas at ED12.5 it w as necessary to open the chest; at ED13.5-14.5, fluorescent imaging wi th the use of microinjection of fluorescein-conjugated albumin was nec essary to visualize the LV chamber. At ED10.5-11, the LV end-diastolic volumes averaged 0.16 mu l (n = 14), and at ED13.5-14.5, they average d 0.57 mu l (n = 16). At both ages there was a positive linear relatio nship between the LV end-diastolic volume and the stroke volume despit e substantial variations in individual heart rates, reflecting the rel ative uniformity of the LV ejection fractions within each age group. T he average of the individual ejection fractions was 27.4% at ED10.5-11 and 58.4% at ED13.5-14.5, the latter being within the normal range fo r the adult rodent heart. These methods will be useful for assessing i n vivo cardiac function at ED10.5 and older murine embryos in litters of transgenic or gene-targeted mice when the mutation leads to later e mbryonic lethality.