Effect of Actinomycin D on Hormones That Control the Release of Thyrotropin from the Anterior Pituitary Glands of Mice

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Abstract
TRF [thyrotropin-releasing factor] and T3 [L-triiodothyronine] have been shown previously to act on the anterior pituitary gland (APG), T3 inhibiting the releasing activity of TRF in a quantitative fashion. This study shows that actinomycin D can prevent or impair the inhibiting effect of T3 on release of TSH by TRF. Actinomycin D inhibited this T3 effect even when the antibiotic was administered 6 hr. before the injection of T3. When actinomycin D was administered 1 hr. after the injection of T3, it essentially had no effect on this T3 action. The effect of actinomycin D on the T3 block probably does not occur by decreasing the uptake of T3 into the APG. When actinomycin D was given to mice in amounts and at time intervals known to decrease the T3 block, it was found that the total RNA synthesis was decreased by 50% in APG but protein synthesis was not impaired. As reported previously for puromycin and cycloheximide, actinomycin D does not affect the TRF-TSH release response.