Hyperresponsiveness of residual thyroid lobe of hemithyroidectomised rat to thyrotropin.

The effects of hemithyroidectomy and thyrotropin administration on rat thyroid gland function were studied in adult male rats. Immediately after surgery or sham operation rats were treated daily with 0.12 IU of bovine thyrotropin (TSH) for 3 or 5 days. In control rats TSH dose applied resulted in an increase in serum T4 level at day 5 of experiment. Serum thyroxine concentration markedly decreased in sham operated and hemithyroidectomised rats, an effect observed at days 3 and 5 of experiment. TSH administration had no effect on serum T4 concentration in sham operated rats while in hemithyroidectomised animals such a treatment resulted in a marked increase in serum T4 level, a phenomenon observed in both time intervals studied. The reasons for hemithyroidectomy-induced hyperresponsiveness of rat thyroid residual lobe to thyrotropin are unknown.