Relative Rates of Exchange of Potassium-42 by the Fœtal Metanephros and Fœtal Liver

Abstract

WALKER et al. ¹ and Ginsberg et al. ² have shown that the kidney of the adult rat exchanges potassium-42 at higher rates than any other organ. After 2 min. the radioactivity of the kidney is eight times that of the liver². We have studied the relative rates of exchange of potassium-42 in the liver and kidneys of 24 rat foetuses at the 20th or 21st day of development. 100 µc. of potassium-42 were injected into the tail vein of twelve pregnant rats at the 20th or 21st day of pregnancy and 2 min. later two foetuses were removed and the kidneys and liver excised. These organs were frozen with cardice to prevent dehydration, weighed to 0.1 mgm., digested in concentrated nitric acid and their radioactivity determined. The results were expressed as the ratio of the number of counts of potassium-42 per min. per mgm. of fœtal kidney to the number of counts of potassium-42 per min. per mgm. of fœtal liver. The total amount of potassium per mgm. of fœtal kidney and liver was also estimated in six fœtuses using a Warren flame spectrophotometer³.