Stimulation of proteolysis in the mouse thyroid gland by thyrotropin and the long-acting thyroid stimulator: comparison of intact lobe and homogenate.

Abstract

Thyrotropin given in vivo stimulated in vitro proteolysis of 125I-labeled thyroglobulin in the thyroid of mice; with intact lobes optimal pH was 7.4 and in homogenates proteolysis was maximal at pH 5.0. The stimulation of proteolysis in intact lobes was otherwise similar to that observed using homogenates. The lowest dose of thyrotropin that gave a significant response was 1 mU in normal mice and 0.1 mU in mice treated with thyroid hormone. LATS given in vivo significantly increased the in vitro proteolysis of endogenous thyroglobulin. There was enrichment of both radioactivity and proteolytic activity in the 15,000 ×g pellet of thyroid homogenate after in vivo administration of thyrotropin, but not if there was an intervening period of incubation of intact lobes before homogenization. Actinomycin D pretreatment,known to inhibit the release of radioiodine from the mouse thyroid in vivo, partly reduced the thyrotropin-induced stimulation of proteolysis at pH 7.4 as well as at pH 5.0. When rat thyroglobulin...