Fluospheres for cardiovascular phenotyping genetically modified mice

Assessment of systemic and regional hemodynamic phenotypes in genetically e ngineered mice by nonradioactive methods is yet an unsolved problem. We the refore investigated whether the reference sample method using fluorescent m icrospheres (FMs), already validated in rats, might be used for this purpos e in C57BL/6 and in apolipoprotein E (ApoE)-deficient mice. FMs were inject ed into the left ventricle of instrumented anesthetized mice. In 10-week-ol d C57BL/6, cardiac output was 18-19 ml/min, and its regional distribution u nder basal conditions was similar to 1.5% (brain), 3.5% (heart), 9.1% (left kidney), 9.8% (right kidney), 1% (spleen), and 0.8% (stomach) (i.e., value s similar to those previously reported with radioactive microspheres). Prop er mixing of FMs was achieved as both kidneys had identical flows; distribu tion of two differently labeled FMs injected simultaneously was shown to be identical by an agreement study, and FM trapping in the capillary bed was demonstrated both histologically and by the recovery in the lungs of 90% of intravenously injected FMs. In addition, identical values for cardiac outp ut and its distribution were obtained in different age-matched groups of C5 7BL/6. The FM technique also proved to be able to evidence angiotensin II a nd isoprenaline classic systemic and regional hemodynamic effects. Finally, applied to 30-week-old ApoE-deficient mice and age-matched C57BL/6, the FM technique showed no major hemodynamic difference between the two groups, e xcept for coronary blood flow, which was significantly decreased in ApoE-de ficient mice. In conclusion, we demonstrated for the first time the feasibi lity, accuracy, and reliability of the FM technique at characterizing the c ardiovascular phenotype of genetically engineered mice.