EndocrinologyJun 1, 1987

How Low Thyroid and Thyroid Hormone Treatment Affect Hormone-Related Messages in the Pituitary Gland

Circadian Biology Weekly Brief ↗PubMed ↗DOI ↗

Updated Mar 31, 2026

Abstract

Marked increases in serum TSH and TSH beta and alpha mRNA were found in hypothyroidism.

Hypothyroidism resulted in higher levels of TSH beta and alpha-subunit mRNA in rat pituitary cells.
72 hours after starting T3 replacement, serum TSH and TSH mRNA levels normalized.
The increase in TSH beta mRNA was more pronounced than the increase in alpha mRNA, indicating different regulatory mechanisms.
Serum TSH levels dropped rapidly following T3 administration, while TSH mRNA levels initially rose before decreasing to normal levels.
Hypothyroidism decreased GH and PRL mRNA levels, which increased after T3 treatment, but LH beta mRNA levels remained unchanged.

Simplified

We have studied the influence of hypothyroidism and thyroid hormone replacement in vivo on rat pituitary cytoplasmic concentrations of TSH beta and alpha-subunit mRNA, measured by cytoplasmic dot hybridization, as well as circulating TSH and pituitary TSH content. Cytoplasmic concentrations of GH, PRL, and LH beta-subunit mRNA were measured in parallel. Marked increases in serum TSH and TSH beta and alpha mRNA were found in hypothyroidism; these changes reversed 72 h after beginning T3 replacement. A more marked effect of hypothyroidism on TSH beta mRNA than on alpha mRNA was evident, suggesting differential control of regulation of the TSH genes. In contrast to a rapid fall in serum TSH after T3 administration, an increase in TSH beta and alpha mRNA was evident at 1 and 6 h, followed by a later fall in TSH mRNA to euthyroid values. Pituitary cytoplasmic concentrations of GH and PRL mRNA were reduced in hypothyroidism and increased after administration of T3; LH beta mRNA was unaffected by hypothyroidism or T3 replacement. The differential effects of thyroid status on TSH, GH, PRL, and LH mRNA indicate specificity of regulation of these anterior pituitary hormone genes.

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How Low Thyroid and Thyroid Hormone Treatment Affect Hormone-Related Messages in the Pituitary Gland

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