Thyroid hormone decreases thyrotropin subunit mRNA levels in rat anterior pituitary.

Recombinant DNA clones containing sequences for the subunits of rat thyrotropin have been isolated, characterized, and used to examine the hormonal regulation of subunit mRNA levels. A library of rat cDNA sequences cloned in plasmid pBR322 was constructed and screened for thyrotropin sequences using cloned bovine cDNAs which had been previously identified. The identity of rat thyrotropin subunit cDNAs was confirmed by nucleotide sequence analysis. The cloned cDNAs were then used as hybridization probes to examine the effects of triiodothyronine on the levels of the alpha- and beta-subunit mRNAs of thyrotropin. The results demonstrate that treatment with thyroid hormone decreases the levels of both alpha- and beta-subunit mRNA in rat anterior pituitary.