A synergism between thymus and pituitary glands was demonstrated in hypophysectomized and thymectomized rats. When given adequate pituitary growth hormone, the growth rate of these rats was directly dependent upon the amount of thymic hormone supplied. One major interaction between thymus and adrenals is the atrophy of thymus following administration of steroids. This becomes a major factor following periods of stress and opposes radiation hormesis in traumatic events, such as war or a nuclear plant explosion. As Selye has demonstrated, mild stress provides the opposite effect, the general adaptation syndrome.
Thymic hormones contribute to lymphocyte maturation and differentiation.
These actions have direct effects upon radiation hormesis in immunity. It was suggested that the devastation from large doses of ionizing radiation follows the destruction of thymus as well as lymphatic organs. This stops the production of differentiated lymphocytes and prevents recovery from severe radiation sickness. The individual becomes highly susceptible to unusually severe infections. The radiation syndrome in guinea pigs was greatly improved by injection of thymic hormone preparations.