[Increase in thyroxine level in blood plasma of hypothyroid rats after administering histones]

It has been shown that the administration of total histones (H1, H3, H2B, H2A, H4), the total histones without histones H4 (H1, H3, H2B, H2A), H1 histones at concentrations of 0.001 and 1 microgram per 100 g of body weight (low and high concentrations) to intact rats during 6 days leads to the decrease of T4 amount in the blood plasm. The total histones and histone H1 at low concentration decrease the T4 amount by the coefficients 5.2 and 5.8 respectively. The corresponding coefficients for high concentration are 2.6 and 1.2. There is no difference in the action of the total histones and H1 histone at low concentration. Low concentration of histones is more effective for the decrease of T4 amount than the high one or than the antithyroid agents mercasolyl and LiCl (3 mg and 2 mM per .100 g of body weight), which decrease the amount of T4 in intact rats by the coefficient 3.6 in 38 days. Administration of histones decreases the amount of T4 in the intact rats but, on the contrary, the 3-4 fold increase is observed in hypothyroid rats, so the amount of T4 is practically reverted to the level of intact rats. The mechanism of regulation of the amount of T4 by histones is discussed.