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Full thickness burns of 30% TBSA by napalm was inflicted to rats and the pathologi-cal changes of the thyroid were observed with optical and electron microscopy and with peroxi-dase histoehemistry for 15 days postburn.Dynamic changes of the serum level of T

3

and T

4

wereobserved concomitantly.It was found that the postburn pathological changes of the thyroid couldbe distinguished into 3 phases as follows:The phase of injury inhibition.This lasted from the 2nd to the 24th hour postburn and wascharacterized by marked damage of the follicular epithelium.The phase of structural and functional recovery.This lasted from the 3rd to 6th day post-burn and was characterized by abated damage of the thyroid and a tendency to recover.The phase of active function.This lasted from the 10th to the 15th day postburn.The syn-thesizing and releasing organellae of the thyroid were well-restored.The changes of T

4

were parallel to the pathological changes of the thyroid in all the stages

while T

3

level was continously inhibited because of the low serum level of T

4

the metabolic dis-turbance of T

4

deiodination

and the inhibition of thyroid secretion in the early postburn stage andthe metabolic disturbance of T

4

deiodination in the middle and late postburn stages.In the earlypostburn stage

the inhibition on thyroid peroxidase was an important factor to inhibit the func-tion of the thyroid.