The effect of glutaurine on thyroid hormones in the rat

Glutaurine (gamma-L-glutamyl taurine), a proposed hormone isolated from parathyroid gland oxyphil cells, was examined for its effect on circulating thyroid hormones in the rat. In acute experiments performed over a 24 hr. period, glutaurine depressed plasma triiodothyronine (T3) levels in a dose-dependent manner; however, thyroxine (T4) levels were not affected significantly. In chronic experiments performed over a 2 wk. period, glutaurine significantly increased T3 levels, but, as with acute studies, the effect of T4 levels was not significantly altered. Following acute glutaurine administration, TSH levels were elevated above control. The increased T3 observed following chronic glutaurine administration may be due to a secondary increase in TSH levels. These data support the hypothesis that glutaurine aids in peripheral thyroid hormonal regulation. Observed differences between acute and chronic glutaurine action are though to result from the effect of glutaurine on the negative feedback inhibiting action of TSH.