Effect of Thyrotropin on the Weight, Protein, Ribonucleic Acid, and the Radioactive Phosphorus Uptake of Chick Thyroids

Abstract

A single injection of 0.020 U of thyrotropin (TSH) was given 2, 6, 12, 18 or 24 hr before autopsy to day-old chicks. The dry weight of the thyroids and the total thyroidal protein were significantly decreased by 2 hr after TSH stimulation. The total ribonucleic acid (RNA) in the thyroids was significantly increased by 12 hr after TSH administration. The ³²P incorporation into the whole thyroid gland, the trichloroacetic acid (TCA) soluble, the ethyl alcohol soluble, the RNA and the TCA precipitate fractions of thyroids was increased by TSH treatment. The greatest and earliest increase was in the TCA soluble fraction, and, as ³²P was lost from this fraction, it increased in the other fractions of stimulated glands. The ³²P uptake into subcellular components such as nuclei, mitochondria and microsomes was significantly increased by at least 12 hr after TSH injection, but the 100,000 g supernatant of thyroids showed a significantly increased uptake by 2 hr after TSH. This was the most heavily labeled cellular compartment. The uridine-¹⁴C incorporation into the RNA and TCA soluble fraction of thyroids was increased by 2 hr after the TSH was given, indicating that the synthesis of RNA begins to increase soon after TSH stimulation, although increases in the total amount of RNA were not significantly changed until 12 hr after hormonal treatment. The incorporation of the labeled uridine into RNA appeared to reflect the amount of label in the TCA soluble phase. The results indicate that, at the time intervals studied, a single injection of TSH involves many cellular reactions. (Endocrinology76: 1124, 1965)