Effect of Alternate-Day Hydrocortisone Therapy on the Immunologically Immature Rat. I: Effect on Blood Cell Count, Immunoglobulin Concentrations, and Body and Organ Weights

Abstract

The effect of 400 mg/M2/day of hydrocortisone, given alternatively from day 7 to day 19, was studied in the immunologically immature rat, a steroid-sensitive species. Animals, sacrificed 2 days following the completion of treatment, suffered from an underweight thymus and spleen, leucocytosis, and peripheral lymphocytopenia, probably not due to redistribution of lymphocytes from blood to tissues. In addition, a significant decrease in serum IgM concentration, reflecting a deficit in primary immune response, was evidenced. Although the percentage of lymphocytes returned to normal in rats sacrificed 23 days after treatment, an overweight thymus and spleen and persistent leucocytosis may reflect a compensatory overactivity of the developing immune system. In contrast, serum IgM concentration increased, but to a value less than normal. An indirect effect of hydrocortisone on lymphocytes through its action on thymus, as well as a direct effect on B cells, is suggested. Unlike humans, alternate-day steroid therapy delayed the normal growth pattern of rat, with a defective rate of growth only during the treatment period.