Accumulation of a large component related to thyrotropin subunits in the pituitary of thyroidectomized rats.

Rat pituitary thyrotropin-β subunit immunoreactivity is demonstrated to increase with time after thyroidectomy. This increase is due to free β subunits and a high molecular weight form. The latter is also immunoreactive in α subunit and native thyrotropin assays. Its immunological properties in these three types of assays respectively, suggest that it represents a “bid β subunit” and a “big α subunit” excluded together in Sephadex G-100 chromatography, rather than a “big thyrotropin”. These larger species could be precursor forms of the subunits. This would be in agreement with the concept of separate biosynthesis of the subunits of pituitary glycoproteic hormones.