Vasoactive intestinal peptide enhances thyroidal iodide uptake during dietary iodine deficiency.

The presence of vasoactive intestinal peptide and neuropeptide Y in thyroid nerves and their effects on thyroid blood flow are well known. However, the effects of these two neuropeptides on the various processes involved in thyroid hormone biosynthesis and release have not been fully explored. We have now tested these two peptides for effects on an early step in thyroid hormone biosynthesis, namely iodide uptake, a process which is comprised of trapping and organification. In these experiments, we have used anesthetized adult male rats pretreated with thyroxine or fed a low iodine diet to increase thyroidal sensitivity. Vasoactive intestinal peptide significantly increased iodide uptake in rats fed an iodine deficient diet but not in those fed a normal iodine diet. This effect disappeared if animals were pretreated with propylthiouracil. Neuropeptide Y did not alter iodide uptake in rats on either the low or the high iodine diet, regardless of the presence or absence of propylthiouracil. The effect of vasoactive intestinal peptide on iodide uptake could be due to its influence on the organification of iodine, or on thyroid blood flow, or on both processes.