Regulation of thyrotropin production by mouse pituitary thyrotropic tumor cells in vitro by physiological levels of thyroid hormones.

Abstract

Primary suspension cultures from serially transplanted mouse pituitary thyrotropic tumors were shown to be regulated by physiological levels of thyroid hormones. TSH release was linear for up to 48 h in control cultures and was inhibited progressively after 10, 24, and 48 h in cultures exposed to triiodothyronine (T3), 4.0 nM. TSH release was inhibited up to 55% of control and glucose consumption was stimulated up to 2.6-fold in a dose-dependent fashion by T3 between 0.2 and 4.0 nM. A biphasic dose-dependent relationship for T3 and thyroxine (T4), and TSH production was demonstrated in two series of cultures. TSH production was stimulated progressively by T3 up to 0.1 nM and T4 up to 5 nM. At higher T3 and T4 levels, TSH production was progressively inhibited. Half-maximal inhibition occurred at total medium concentrations of 0.2 nM T3 and 15 nM T4 or free hormone levels of 8 x 10-12 M and 14 X 10-11 M, respectively. High affinity, low capacity nuclear binding sites were demonstrated for T3 and T4. The ap...