DEPENDENCE OF CONVERSION RATIO ON THE DOSE OF RADIOIODINE IN FISH
The effect of I/sup 131/ dose on radioiodine metabolism in goldfish and other teleosts was investigated to ascertain whether so-called tracer doses, used to evaluate thyroid activity, injure thyroid tissue. Five to 400 mu c of carrier-free radioiodide (NaI/sup 131/) was injected intraperitoneally in 0.05 nd of distilled water; 3, 4, or 8 days afterwards the plasma conversion ratios (CR) were determined. The CR represents the extent of turnover of I/sup 131/ to plasma radiohormone and is considered a sensitive discriminatory test for thyroid activity. Goldfish at 20 deg C showed a correlation between the 4-day CR and dose of I/sup 131/ over a dose range of 1.1 to 8.2 mu c/g body mass. Other aspects of I/sup 131/ metabolism did not correlate with dose. Chum salmon at 12 deg C also showed a correlation between CR and dose over a comparable range but goldfish (4 deg C), chub (4 deg and 20 deg C), steelhead trout (4 deg C), and sockeye salmon (4 deg C) showed no dependence of CR on liar dose. Goldfish were unique among these species in possessing ruptured follicles and blood cells in the colloid. Ruptured follicles were also present in uninjected fish and there was no evidence to relate rupturing of follicles with dose-dependence of the CR. Hence, although all species were tested over the same dose range, only goldfish at 20 deg and chum at 12 deg C showed any correlation between CR and dose. Furthermore, the trend estublished in goldfish at 20 deg was absent at 4 deg C. The response of the thyroid to administered I/sup 131/ by increasing the proteinbound iodine (PBI/sup 131/) level seems to be dependent on temperature, general metabolic state, and species. The difference in response between 2 species at the same temperature could be partly due to a difference in general activity of the gland between the two species. It could be due also to a difference in the topography of the scattered thyroid tissue. Where thyroid follicles are compactly arranged, the radiation flux per unit area of follicle will tend to be greater and presumably the harmful effects augmented. It is therefore emphasized that the effects of increasing doses of I/sup 131/ on radioiodide metabolism are difficult to predict. They depend on many factors, prominent among which could be the topography of the thyroidal tissue and also the total amount of I/sup 131/ accumulated by the follicles. It is concluded that doses of 1 mu c/g may be effective in altering I/sup 131/ metabolism, probably by increasing the output of radiohormone. (BBB)
- Research Organization:
- Univ. of British Columbia, Vancouver
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-18-011909
- OSTI ID:
- 4105470
- Journal Information:
- Canadian Journal of Zoology (Canada), Vol. Vol: 41; Other Information: Orig. Receipt Date: 31-DEC-64
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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