Doctoral Dissertations

Date of Award

12-1968

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Animal Science

Major Professor

Eric W. Swanson

Committee Members

J. K. Bletner, R. G. Cragle, J. T. Miles, J. T. Smith

Abstract

The objectives of this study were to (1) investigate the form of the circulating iodine as affected by thiocyanate (SCN) and (2) to deter-mine the effect of SCN on extrathyroidal iodine systems in the bovine. Continuous flow paper electrophoresis, Sephadex G-25 column separation and ascending paper chromatography showed no major differences in the radioiodine compounds present in urine or plasma collected from calves during preliminary periods and periods when 2 to 4 g of NaSCN were fed daily. Thiocyanate affected the proportions of the circulating iodine fractions but the methods used were not capable of detecting possible production of new forms of iodine after SCN feeding. Effect of SCN on radioiodine metabolism was investigated in normal and athyroid (either surgically or radioiodine thyroidectomized) cows and calves. Both control and athyroid animals, with the exception of one athyroid animal, had higher radioiodine excretion in the urine during the period when 2 to 5 g of NaSCN were fed than during the pre-liminary period. Daily SCN administration caused a decrease in radio iodine excreted in the feces when radioiodine was given as a single dose, but did not affect fecal excretion when a daily dose was given. The plasma radioiodine concentration was higher for both athyroid and normal animals when SCN was fed than during the preliminary periods. The increase in plasma radioiodine concentration and the higher urinary radioiodine excretion in both normal and athyroid animals when SCN was fed indicated that the effect of SCN was not dependent on blockage of thyroid competition for circulating iodine. The higher plasma radioiodine concentration in both normal and athyroid animals suggested that the increased urinary radioiodine excretion was due to the elevated plasma levels with consequent greater elimination in the urine. Thiocyanate administration significantly increased the radioiodine clearance, but did not alter the urine flow. This showed that increased urinary radioiodine excretion could occur without higher plasma levels during the SCN period. A simultaneous metabolism of iodide (131I) and triiodide (125I3) in calves resulted in slightly less 125I than 131I excretion in the urine and feces with a slightly lower 125I concentration in plasma. The excretion pattern of the 125I was not similar to the radioiodine excretion patterns after SCN administration and, therefore, eliminated the possibility of an abnormal I3 formation and subsequent excretion upon the administration of SCN to cattle. Two calves received a simultaneous transfusion of plasma from each of two calves dosed with either 15 mCi of 131I or of 125I plus NaSCN. The excretion patterns of 131I and 125I in the transfused calves were identical, but significantly less 125I than 131I was taken up by the thyroid. If the SCN in the transfused plasma was sufficient to cause a decrease, it would have affected both 131I and 125I identi-cally. Since this did not happen, the results indicated that SCN altered the 125I in some manner to make it less available for thyroid uptake. The higher thyroid uptake of 131I than 125I suggested that SCN caused the formation of an abnormal iodine compound in the blood which was not concentrated by the thyroid. However, the lack of a concurrent difference in the urinary excretion pattern between the two isotopes makes it diffi-cult to assess the significance of the thyroid results. In a study with five calves, intravenous injection of 0.33 mM NaSCN per kg of live weight increased the abomasum venous/arterial radioiodine ratio from .77 to .95 and increased the thyroid venous/ arterial ratio from .75 to .94. This indicated that SON exerts a comparable degree of inhibition on iodide uptake by both systems. The mixed saliva/plasma ratio was decreased from .72 to .51 upon the administration of the NaSCN. In two additional calves fitted with paro-tid cannulas, 0.33 mM NaSCN per kg of live weight decreased the saliva/ plasma ratio from 1.30 to .27. Feeding 10 g of NaSCN to lactating cows decreased the cumulative percentage of an oral radioiodine dose appearing in a 5-day milking from 6.9 to 2.9 in normal and 10. to 3.5 in hypothyroid cows. Milk/ plasma ratios decreased from 1.6 to 0.6 in normal and 3.5 to 0.8 in hypothyroid cows.

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