Ipsilateral thyroid growth and depressed thyroid hormone synthesis and content after unilateral superior cervical...

The role of the sympathetic nervous system in the control of the goitrogenic response was examined in adult male rats subjected to unilateral superior cervical ganglionectomy 12-30 days earlier. A spontaneous goiter as well as an increased thyroid growth after the administration of the goitrogenic agents methylmercaptoimidazole and thyrotropic stimulating hormone (TSH) were found in the ipsilateral lobe. Norepinephrine and epinephrine content decreased significantly by 80 and 31%, and thyroxine (T4) and triiodothyronine (T3) content by 24 and 15%, in the ipsilateral lobe. After the injection of a tracer dose of 125I, percent radioactivity incorporation to diiodotyrosine (DIT) was higher, and that to monoiodotyrosine (MIT) lower, in the ipsilateral lobe; additionally a lower ratio "labeled T3 + T4/labeled DIT" was found in the denervated thyroid lobe. These results suggest that the sympathetic nerve terminals in the thyroid gland modulate the organ's response to circulating TSH.