[Thyrotropic activity of the pituitary gland in rats at various age periods].

The thyrotropic activity of the hypophysis (TTH synthesis and secretion) was studied in rats at various age periods. The work was conducted on mongrel male rats of four age groups: 1 1/2-2, 8-10, 18-24, and 28-32-months old. Being relatively low in the sexually immature animals, the thyrotropic activity of the hypophysis considerably intensified in adult rats and diminished with the ageing of the organism. A reduction of the TTH synthesis and secretion in old animals, testified to by the hormone content in the hypophysis and the blood, was apparently connected with the intensification of the T4-deiodating capacity of the hypophysis tissue.