Estrogenic hormones regularly cause acute thymic involution in the intact animal (1, 2). Their effects on lymphatic tissues other than the thymus are minimal, are quite variable, and appear to relate to the species studied. Within the last two years we have investigated the effect of estradiol on lymphatic tissues and the immune system when administered to normal adult, newborn, and sublethally or lethally irradiated mice protected by syngeneic and allogeneic bone marrow. When 0.5 mg of estradiol was given to adult normal female mice, three times weekly over a 6-week peiiod, involution of the thymus occurred within the first week and was marked at 6 weeks (3). Hepatomegaly first appeared within 2 weeks and partially regressed by 6 weeks. Microscopically, this was associated with Kupffer cell hyperplasia, but no other obvious histologic change. The lymph node and the splenic white pulp were not grossly or histologically altered, but there was a slight reduction in the absolute lymphocyte count noted in the peripheral blood after 6 weeks of therapy. Extramedullary hematopoiesis increased within the first week. Anemia, weight loss, and death did not occur. The homograft and hemagglutination responses were unaffected (J. S. Thompson, unpublished data). By contrast, the administration of estradiol to newborn mice induced a wasting syndrome characterized by ruffled fur, diarrhea, weight loss, both central and peripheral lymphoid hypoplasia, and increased mortality (4). Furthermore, if estradiol was injected for 2 weeks after irradiation of adult mice, impaired recovery of the thymus and other lymphatic tissues was associated with increased mortality
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Jan 1, 1967
U Haelst 
