ALTERED RESPONSE OF BLOOD THYROXINE LEVEL AFTER ITS ACUTE DEPLETION BY ISOVOLEMIC EXCHANGE-TRANSFUSION IN RATS WITH LESIONS IN HYPOTHALAMUS AND THALAMUS

  • 1 January 1976
    • journal article
    • research article
    • Vol. 10  (1) , 29-36
Abstract
Bilateral electrolytic lesions were made in various areas of the hypothalamus or thalamus on the 6th day of a period of daily radioiodide (1 or 5 .mu.Ci 125I-daily per animal) in male rats weighing about 350 g. Such injections were continued for another 4 days and after 2 days of intermission the blood thyroid hormone was acutely depleted by isovolemic exchange transfusion of thyroid hormone free blood cell suspension. Relative changes of plasma thyroxine (T4) level were measured with the aid of paper chromatography in small aliquots of plasma frequently taken from the animals under maintained isovolemia by replacing the removed plasma. In animals with various bilateral electrolytic lesions in the hypothalamus (suprachiasmatic and paraventricular areas) the response of the blood T4 level after the transfusion is similar to that in sham-operated controls bearing unilateral subcortical lesions or in normal animals. The response in animals with thalamic lesions resembled that observed previously in thyroidectomized animals. Since the blood T4 level change presumably results from changes of pituitary thyrotropic activity, in rats with thalamic lesions the normal response of the hypothalamo-pituitary-thyroid axis was prevented. The mechanism remains to be elucidated.