Lymphocyte kinetic studies employing 51-chromium-labeled autologous lymphocytes were performed in nine normal volunteers in order to determine the effects of
hydrocortisone administration on the recirculating versus the nonrecirculating intravascular lymphocyte pools. Following infusion of labeled cells, the recirculating portion of the labeled cells rapidly equilibrated with the total intravascular lymphocyte pool and the vastly larger total-body recirculating lymphocyte pool, so that by 1 hr following infusion 21.8% plus or minus 3.2% of the labeled lymphocytes were left in the circulation. Four hundred milligrams of intravenous
hydrocortisone administered 24 hr after infusion of labeled cells caused a profound but transient
lymphocytopenia which was maximal at 4 hr with return of lymphocyte counts to normal by 24 hr after injection. Concomitant with the
lymphocytopenia there was a dramatic increase in lymphocyte specific activity (cpm per 10-6 lymphocytes), while the total lymphocyte-associated radioactivity remaining in the circulation was unchanged, indicating that
corticosteroid administration depleted the unlabeled recirculating cells. As the lymphocyte counts returned to normal following
hydrocortisone, the specific activity also returned to normal. These studies indicated that
hydrocortisone administration caused a transient
lymphocytopenia by a preferential depletion of the recirculating portion of the intravascular lymphocyte pool