HORMONAL-CONTROL OF INTESTINAL FC RECEPTOR GENE-EXPRESSION AND IMMUNOGLOBULIN TRANSPORT IN SUCKLING RATS

Hormonal control of immunoglobulin (Ig) absorption and of intestinal F c receptor mRNA expression were investigated in rats to assess its pot ential role in the normal postsuckling inhibition of this transport sy stem. Corticosterone and L-thyroxine therapy caused premature inhibiti on of the absorption of orally administered murine monoclonal antibody and of Fc receptor mRNA expression in a dose- and time-dependent mann er. Low-dose corticosterone had no effect on Fc receptor mRNA synthesi s after 3 d but decreased Ig transport fivefold after 7 d. High dose c orticosterone resulted in a threefold reduction in Fc receptor after 3 d, and there was almost complete inhibition (> 30-fold) of transport and of Fc receptor transcript levels after 7 d. Similarly, 7 d of high -dose thyroxine decreased both serum Ig transport and Fc receptor (> 3 0-fold). However, adrenalectomy did not prevent the normal post-suckli ng declines in Ig transport or receptor synthesis. This study demonstr ates that exogenous corticosteroids and thyroxine hormone inhibit Ig t ransport and steady-state duodenal Fc receptor mRNA levels in suckling rats. Endogenous adrenal steroids however, do not appear to be entire ly responsible for the age-dependent decline in this transport system.