Expression of preproNPY and precursor VIP mRNAs in rats under hypo- or hyperthyroid conditions.

Both neuropeptide Y (NPY) and vasoactive intestinal peptide (VIP) are present in thyroid nerves and have been shown to alter thyroid activity. The present study was conducted to determine whether hypo- or hyperthyroidism is associated with changes in the expression of the mRNAs for these neuropeptides in the major ganglia which supply nerves to the thyroid or within the thyroid gland itself. Hypo- or hyperthyroid conditions were induced by the administration of propylthiouracil (PTU) or thyroxine (T(4)), respectively, for 6 days. Control rats received vehicle injections. Total RNA from superior cervical ganglia (SCG), local thyroid ganglia, thyroid gland, and selected other tissues was extracted and mRNA levels were analyzed using Northern blot procedures. No significant changes in preproNPY or precursor VIP mRNA levels were detected in the SCG or the local thyroid ganglia in response to PTU or T(4) treatment. However, PTU treatment was associated with an increase in preproNPY mRNA levels in the thyroid gland itself. These results indicate that changes within the thyroid axis in response to these hypo- and hyperthyroid conditions do not include alterations in steady-state preproNPY or precursor VIP mRNA concentrations in the major ganglia which supply nerves to the thyroid gland. However, intrathyroidal preproNPY mRNA levels are increased as a consequence of the thyroidal adaptation to a PTU challenge.