EFFECT OF GROWTH-HORMONE AND THYROID-HORMONE ON AUTOIMMUNE-THYROIDITIS IN OBESE CHICKENS

The effect of thyroxine (T-4) and recombinant (rcGH) or purified pitui tary-derived (pcGH) chicken growth hormone on the development of spont aneous autoimmune thyroiditis (SAT) was examined in the Obese strain ( OS) chicken. Day-old OS chicks were randomly assigned to a control or 1.0 ppm T-4 supplemented diet and a vehicle or 500 mu g rcGH/kg BW dai ly injection, using a 2 x 2 factorial design. At 4 weeks, sera were an alyzed for anti-thyroglobulin autoantibody (TgAAb) using a kinetics-ba sed ELISA. Leucocytic infiltration of the thyroid was assessed using c omputer-based video imaging techniques. A close correlation between Tg AAb and thyroid infiltration was seen with both being decreased (p < 0 .05) by the T-4/rcGH treatment. Neither the T-4 or rcGH alone produced this effect and the rcGH treatment significantly elevated TgAAb. In a second experiment, all but the control group received 1.0 ppm T-4 sup plementation and two of the T-4-treated groups received either 50 or 2 00 mu g pcGH/kg BW by daily injection, As before, T-4/pcGH signifi can tly reduced TgAAb and thyroid infiltration. T-4 alone produced no sign ificant effects. These data support the conclusion that the combined t reatment of T-4 and cGH exert an immuno-modulatory effect within a str ain that is predisposed to autoimmune thyroiditis while GH treatment a lone exacerbated the condition.