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Some factors affecting radioiodide metabolism in the threespine stickleback Gasterosteus aculeatus Linnaeus Wiggs, Alfred James

Abstract

Excretion of radioiodide by Gasterosteus aculeatus has been shown to vary directly with increases in salinity and inversely with size of fish. Erroneous excretion values may be produced by an apparent laboratory diuresis which seems to vary with season and salinity. During the initial stages of sexual maturation in sea water temporary changes in excretion occur which result in an increased retention of radioiodide by the fish. These changes show a greater development at lower salinities. The demonstrated dependence of thyroid uptake upon available radioiodide make this parameter an unreliable estimate of thyroid activity. The conversion ratio, except for errors which occur under conditions where the rate of radioiodide excretion is not constant over the period of the measurements, seems to be a valid estimate of thyroid activity. Technical factors, such as the binding of inorganic radioiodide to precipitated protein, can also produce erroneous conversion ratio values. Differences in the protein binding of inorganic radioiodide suggest that changes in blood proteins occur during sexual maturation. Although a seasonal increase in thyroid activity occurs there is no correlation between this and the increase in radioiodide retention. There is therefore no reason to believe that the thyroid is responsible for the observed changes in retention of radioiodide.

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