Publication Date


Document Type


First Advisor

Prahlad, K. V.

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Biological Sciences


Thyroid hormones


The effects of exogenous 17B-estradiol and progesterone on thyroidal activity in the ovariectomized rat were assayed in the present study. Progesterone administration at a 3 mg. dose level for three consecutive days prior to 125I administration had no effect on iodine uptake by the thyroid gland. The concentration of 125I remained similar to that of the control group from 12 to 72 hours after administration. On the other hand, the administration of 17B-estradiol at a 3ug dose level for three consecutive days did cause a subsequent threefold increase over the control values with respect total iodine uptake by the thyroid gland. The increase in concentration of 125I remained significantly higher than that of the controls from 12 to 72 hours post-administration. Both controls and estrogen-treated rats showed slight decreases in concentrations of 125I by 72 hours after administration. The effects of 17B-estradiol on synthesis of the various iodinated fractions within the thyroid gland were measured at 12 and 48 hours after 125I administration. Administration of 3 ug of 17B-estradiol for three consecutive days resulted in major increases in the syntheses of diiodotyrosine, mono-iodotyrosine, thyroxine, diiodothyronine and triiodothyronine to values well over those of the controls at both 12 hours and 48 hours post-125I administration. In addition, an increase in the free iodide fraction was seen at both time intervals. Although the absolute concentration of each fraction was much greater in the estrogen-treated group, the proportions of the fractions were similar to those of the controls at both 12 hours and 48 hours after 125I administration. This indicates that the previously observed effects of estrogen administration on circulating thyroid hormone levels in the rat are the result of extrathyroidal conversion of thyroxine to triiodothyronine rather than alteration in hormone synthesis within the gland itself. Within both the control and estrogen-treated groups, the proportions of thyroxine and T2+3 increased during the interval extending from 12 to 48 hours post-125I administration, whereas the proportions of monoiodotyrosine and diiodotyrosine decreased over this time period. This indicates an increase in hormone synthesis from precursor compounds by 48 hours after 125I administration.


54 pages




Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

Media Type