The Thyroxine Secretion Rate of Growing Turkey Poults

MIXNER et al. (1944) developed a method for the estimation of the mean thyroxine secretion rate of groups of growing birds by modifying the technique of Dempsey and Astwood (1943) used in determining the influence of temperature upon the thyroxine secretion rate of rats. It is based upon the observation that thiouracil and other goitrogenic chemicals depress the thyroxine secretion of the thyroid gland and thus upset the equilibrium of endogenous thyroxine and thyrotropin secretion. The pituitary immediately increases the thyrotropin secretion rate and causes hyperplasia of the thyroid gland (goiter). The daily injection of exogenous thyroxine to such birds sufficient to prevent thyroid hyperplasia was considered to represent the mean daily thyroxine secretion rate of the group of birds. The thyroxine secreted by the thyroid gland is in the 1- or levo-form, whereas the form of injected thyroxine in the past has usually been of the racemized d, 1-form… .