To study the effects of altered thyroid status on pretranslational control of pituitary hormones, adult male rats were given propylthiouracil for 6 weeks and underwent the following studies. 1) Rats were injected with T3 at 10 μg/100 g BW daily for 10 days. 2) Rats were given T3 injections at 0, 0.01, 0.1, 1.0, or 10 μg/100 g BW for 10 days. 3) Rats were killed 0, 1, 6, or 24 h after a single injection of T3 at 10 μg/100 g BW or after 5 or 10 days of daily T3 injections. Pituitary mRNA concentrations of TSH β, α-subunit, PRL, GH, POMC, FSH β, and LH β were determined for individual animals. Marked increases in TSH β and a-subunit mRNAs occurred after PTU treatment, and these changes were reversed by 1.0 μg/100 g BW T3 and within 24 h of a single T3 injection of 10 μg/100 g BW. Further increases in the dose or time course of T3 administration led to a relatively greater suppression of TSH β mRNA levels than α-subunit mRNA levels. In contrast, GH and PRL mRNA levels were low in hypothyroid animals, and both rose toward control levels with 0.1 μg/100 g BW T3 and by 24 h after a single T3 dose. Induction of hyperthyroidism did not further increase GH mRNA levels above control, but increased PRL mRNA levels 2-fold over control. No changes were seen in FSH β, LH β, or POMC mRNA levels with any treatment. Thus, studies of altered thyroid status in the rat reveal dose-response and timecourse variability in the pretranslational control of TSH β, asubunit, GH, and PRL by thyroid hormone.
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