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Table of Contents | |
THYROIDECTOMY (SURGICAL REMOVAL OF THE THYROID GLAND)
What are the consequences of thyroidectomy? Here is a study showing that
thyroidectomy reduces testosterone production in male rats. Replacement hormone
normalizes testosterone production.
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J Cell Biochem 1999 Jun 15;73(4):554-62 |
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Regulation of thyroid hormones on the production of
testosterone in rats.
Chiao YC, Lee HY, Wang SW, Hwang JJ, Chien CH, Huang SW, Lu CC, Chen JJ,
Tsai SC, Wang PS
Department of Physiology, Schools of Life Science and Medicine, National
Yang-Ming University, Taipei, Taiwan, Republic of China.
The effects of a thyroidectomy and thyroxine (T4) replacement on the
spontaneous and human chorionic gonadotropin (hCG)-stimulated secretion of
testosterone and the production of adenosine 3',5'-cyclic monophosphate (cAMP)
in rat testes were studied. Thyroidectomy decreased the basal levels of
plasma luteinizing hormone (LH) and testosterone, which delayed the maximal
response of testosterone to gonadotropin-releasing hormone (GnRH) and hCG in
male rats. T4 replacement in thyroparathyroidectomized (Tx) rats restored
the concentrations of plasma LH and testosterone to euthyroid levels.
Thyroidectomy decreased the basal release of hypothalamic GnRH, pituitary LH,
and testicular testosterone as well as the LH response to GnRH and
testosterone response to hCG in vitro. T4 replacement in Tx rats restored
the in vitro release of GnRH, GnRH-stimulated LH release as well as hCG-stimulated
testosterone release. Administration of T4 in vitro restored the release of
testosterone by rat testicular interstitial cells (TICs). The increase of
testosterone release in response to forskolin and androstenedione was less
in TICs from Tx rats than in that from sham Tx rats. Administration of
nifedipine in vitro resulted in a decrease of testosterone release by TICs
from sham Tx but not from Tx rats. The basal level of cAMP in TICs was
decreased by thyroidectomy. The increased accumulation of cAMP in TICs
following administration of forskolin was eliminated in Tx rats. T4
replacement in Tx restored the testosterone response to forskolin. But the
testosterone response to androstenedione and the cAMP response to forskolin
in TICs was not restored by T4 in Tx rats. These results suggest that the
inhibitory effect of a thyroidectomy on the production of testosterone in
rat TICs is in part due to: 1) the decreased basal secretion of pituitary LH
and its response to GnRH; 2) the decreased response of TICs to gonadotropin;
and 3) the diminished production of cAMP, influx of calcium, and activity of
17beta-HSD. T4 may enhance testosterone production by acting directly at the
testicular interstitial cells of Tx rats.
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