Effect of Stimulation of the Vagus Nerve on the Thyroidal Release of131I-Labeled Hormones

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Abstract
Effects of electrical stimulation of the vagus nerve on the content of PB131I [protein-bound iodine] in thyroid venous blood were studied in dogs. After stimulating the nodose ganglion on either side, the concentration of the PB131I in thyroid venous blood and the PB131I output from the thyroid increased in all 14 cases. Unilateral nodose ganglion stimulation facilitated the secretion of PB131I bilaterally, the increase on the stimulated side being always more pronounced than the other. The PB131I response to nervous stimulation was characterized by a prompt increase within 15 min. Effects of stimulation of the vago-accessory myelencephalic rootlets of the vagus nerve were also investigated to ascertain the pathway through which the nervous stimulus was transmitted to the thyroid for secretion of its hormone. Regulation of thyroid hormone secretion by the vagus nerve depends mainly on fibers passing through the main stem of the vagus among its original rootlets. A significant increase in thyroid blood flow was observed in the group which had vagal stimulation only; and a marked increase was observed in the group which had had a previous sympathectomy. Stimulation of the vagus nerve accelerated the secretion of thyroid hormones by increasing the blood flow rate and its hormone concentration in the thyroid venous blood. The response of the thyroid gland to neural stimulation appeared more promptly, although it was less pronounced, than the response to TSH [thyroid-stimulating hormone].