131I concentrations in blood, milk, urine and faeces of dairy cows following a single dose of radio-iodine

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Abstract
1. The concentrations of 131I in milk, urine, and faeces were compared to the total and non-proteinbound radio-iodine of blood after a single dose of radio-iodine to cows that were being maintained on diets providing about 3·5 or 12-16 mg. of stable iodine per day.2. In general, the 131I concentrations in milk and urine tended to parallel the non-protein-bound 131I of blood. Faecal 131I levels of the low-iodine cows tended to parallel that of the whole blood, whereas it followed the non-bound radio-iodine of blood for cows on the higher stable iodine diet.3. Compartmental analysis of the concentration curves showed a component with a T½ of from 10 to 22 hr. being common to both groups of cows. The second component of the curves constructed for the cows on the higher iodine intake had a T½ of from 41 to 58 hr. The second component for the low-iodine cows had a T½ that ranged from 83 to 169 hr. for the urine, faeces and non-bound radio-iodine of blood and 1200 and 1580 hr., respectively, for the faecal and whole-blood curves.4. A greater proportion of bound radio-iodine was observed in the milk and blood of cows on the low-iodine diet than for the cows on the higher iodine intake. The proportion of bound 131I in blood increased with time, but the bound 131I of milk was relatively constant.