Characterization of rat placental TRH-like material and the ontogeny of placental and fetal brain TRH.

TRH immunological and biological activity was characterized in rat placental extracts. Placentae were extracted sequentially with 2 N acetic acid and glacial acetic acid. The lyophilized residues were further extracted with 90 per cent methanol, and the extracts were then dried, and reextracted with distilled water. When a 100 000 g supernatant fraction of this extract was utilized for characterization, TRH extracted from the placenta was found to be similar to synthetic TRH by four criteria: parallelism of immunoassay inhibition curves, similarity of elution volumes after Sephadex G-10 chromatography, TRH biological activity (TSH release from rat pituitaries in vitro), and identity on high-pressure liquid chromatography. Between the 16th and 20th day of gestation, placental TRH activity increased nearly threefold, from 10.9 +/- 3.0 to 29.7 +/- 3.7 pg/mg protein. Changes of a similar magnitude were apparent in the fetal brain (6.0 +/- 0.5 to 18.9 +/- 2.4 pg/mg protein). Our studies suggest that TRH activity in the rat placenta increases with gestational age in a pattern similar to that described previously for certain placental protein hormones and developmental changes in fetal brain TRH.