Postnatal development of cardiac output distribution measured by radioactive microspheres in rats.

Distribution of cardiac output was measured in rats, 9, 18, 25, 42 and 64 days old, by means of 85Sr-labelled microspheres 15 micrometer in diameter. The fractions of the cardiac output supplying the heart, lungs, cerebrum, hindbrain, kidney, liver, spleen, stomach, small intestine, large intestine, bones and muscles of the hindlegs and skin were estimated. The values obtained were further related to the relative weights of the respective organs. The distribution of cardiac output changed with age, the changes being most pronounced in the brain, kidney and small intestine.