Effect of leucogenenol, a thymothyroid hormone, on the growth of immature and neonatally thymectomized rats.

ABSTRACT

The reports of early investigators that growth is delayed by thymectomy of immature animals have been confirmed. Although growth is delayed by thymectomy, thymectomized animals approach asymptotically with age the same final weight as corresponding intact animals. Treatment with leucogenenol, a thymothyroid hormone, accelerates the rate of growth of immature neonatally thymectomized rats to that of normal rats. However, treatment with leucogenenol does not increase the rate of growth of normal rats. Treatment with leucogenenol does not change levels of growth hormone (GH) or thyroxine (T4) in the serum of either thymectomized or intact immature and adult rats. Neither is the depression in levels of serum leucogenenol that follows thymectomy associated with a change in serum levels of GH or T4. Thus it is apparent that levels of serum leucogenenol do not affect the rate of growth of immature animals by increasing serum levels of GH or T4. By analogy with the finding that treatment with leucogenenol increases the rate at which committed cells of the bone marrow and cells involved in the immune response develop into functional cells, it is suggested that the levels of serum leucogenenol are one of the factors that determine the rate at which types of body cells that make up bone and other body tissues develop from committed precursors.