A radioimmunoassay for 3,5,3'-triiodothyronine in chicken serum.

A double-antibody radioimmunoassay is described for 3,5,3'-triiodothyronine (T3) in chicken serum. Primary antibody produced in a rabbit had negligible crossreactivity with 3,3,5'-triiodothyronine and thyroxine. The primary antibody diluted 1:1000 bound 50% of a tracer dose of 125I-T3, and a standard curve of 0 to 800 pg/tube was used. Percent binding ranged from 14.1 to 54.1 for a standard curve. Serum volume ranging from 50 to 150 microliter tube did not affect assay results. Coefficient of variation was 2.8% within the assay and 5.5% between assays. The inhibitor 8-anilino-1-naphthalene sulfonic acid was necessary for recovery of T3 from spiked samples. Young chickens had reduced serum T3 concentrations when fed diets containing .1% thiouracil for 14 days when compared with serum T3 concentrations of chickens fed the diet without thiouracil. Feeding .2% thiouracil for 3 days did not affect serum T3 concentration.