Distribution and disappearance of exogenous [125I] big renin in the newborn puppy.

The distribution and metabolism of infused exogenous [125I] inactive plasma big renin, molecular weight 56,000 was studied in five newborn puppies. The animals were sacrificed and the organs removed and studied by chromatography, along with periodic blood samples taken during the 120-min study, for evidence of conversion of high-molecular-weight renin to low-molecular-weight renin. The decay curve suggested an initial rapid distribution (alpha) phase of 10 +/- 1.5 min followed by a slower elimination (beta) phase of 40 +/- 4.6 min [125I]-Big renin was taken up by the red blood cell and released slowly. The liver, kidneys, and lungs had the highest % of [125I]-big renin at the termination of the study. There was no chromatographic evidence of a change in molecular weight of the [125I]-big renin. These data show that big renin has a two-compartment disappearance curve and that there is no evidence of conversion of high-molecular-weight renin to low-molecular-weight renin systemically or in the tissues of the newborn canine puppy.