Immunotoxic effects of exposure of rats to xenobiotics via maternal lactation. Part I 2,3,7,8-tetrachlorodibenzo-p-dioxin.

Exposure of lactating female Leeds rats to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) resulted in a reduction in the body, spleen and liver weights of their male offspring at 130 days of age. None of the total administered doses (0.2, 1.0 or 5.0 micrograms/kg b.wt over 18 days) induced thymic atrophy in the offspring of either sex as adults. Most of the growth inhibition occurred during the suckling period and the effect was near maximal following maternal exposure to the lowest dose of TCDD. After this dose, at post-natal day 130 the body weights of the female offspring remained depressed, while those of the males had recovered to untreated control values. Maternal exposure to TCDD affected the immunocompetence of the adult offspring: in vitro T cell dependent and T cell independent responses and mitogen induced in vitro production of interleukin 1 (IL-1) and interleukin 2 (IL-2) were suppressed at post-natal day 130. The total dose of TCDD that has to be administered to dams over an 18-day nursing period in order to reduce the humoral responses of their offspring as adults by 50% of the maximum was estimated to be in the range 0.3-1.0 micrograms/kg b.wt to the antigens SRBC, DNP-Ficoll or TNP-LPS and 3.5-3.9 micrograms/kg b.wt. to the antigen LPS.