A reappraisal of the goitre-prevention assay: Determination of the thyroid secretion rate in the Japanese quail and the relative potencies of T 3 and T 4 in preventing goitrogenesis

Abstract

This reappraisal shows that the goitre-prevention assay (GPA) is as effective as radiometric techniques for estimating thyroid hormone secretion rates (TSR) in quails ( Coturnix coturnix japonica) and can be used where cost or facilities preclude the use of radioisotopes. A simple modification of GPA results analysis is described which enables calculation of confidence limits of the estimated TSR. Birds were injected subcutaneously twice daily for 20 days with 0.5 ml 0.9% (w/v) NaCl/100 g body wt/day alone (controls) or containing a fixed dose of goitrogen (10 mg 6- n-2-propylthiouracil (PTU)/100 g body wt/day) combined with one of several doses (1.4, 2.1, 2.8, 3.5 μg/100 g body wt/day) of either l-triiodothyronine (T 3) or l-thyroxine (T 4). Thyroid weights (per 100 g body wt) were measured after decapitation on the 21st day. The goitre-preventive doses of T 3 or T 4 (referred to as TRSs) were estimated as the y-intercepts from linear regressions of T 3 or T 4 doses on the differences between the mean thyroid weight of control birds and thyroid weights of PTU-treated birds; TRSs ± 95% confidence limits were 1.81 ± 0.15 (df = 14) for T 3 and 1.67 ± 0.13 (14) μg/100 g body wt/day for T 4.