THE EFFECT OF STEROIDS ON THE CIRCULATING LYMPHOCYTE POPULATION

Abstract

The influence of stress on the circulating lymphocyte
population in rats was studied at different times
after stress stimuli and correlated to the concentra·
tion of corticosterone in serum. A rapid increase of
the corticosterone level, with a duration of about one
hour, was seen in both normal and thymectomized
animals. Female rats showed higher serum levels than
male rats. Depression of thoracic duct lymphocyte
cell levels in normal animals seemed to be maximal
about 3 hours after exposure to stress and restitution
to pretreatment levels was completed within 1- 2
days. The lymph cell population in neonatally thymectomized
animals did not show any significant
changes after stress.
The endogenous corticosterone secretion after stress
gave the same changes in the circulating lymphocyte
population in normal rats as after injection of a
high dose of prednisolone. Because of the absence
of effect on thymectomized animals, the effect of
endogenous secreted corticosteroids seems to be
mainly on T-lymphocytes. The findings suggest the
existence of a circulating highly steroid-sensitive
thymus-dependent lymphocyte population. This
population seems normally to be depressed by stress
mechanisms mediated by adrenal corticosteroid
secretion. There also seems to be a difference be-
tween circulating T- and B-lymphocytes with respect
to sensitivity to low doses of naturally secreted cor-
tico steroids.
Key-Words: Lymphocyte - Thoracic duct - Blood -
Stress - Rat - Thymectomy - Corticosterone