VIP and Hormone Secretion from Thyroidal Follicular and C-Cells

Summary

The effect of vasoactive intestinal peptide (VIP) on the cAMP system of the thyroid and on the secretion of T₄ and T₃ from the follicular cells and calcitonin and somatostatin from the C-cells was studied in perfused dog thyroid lobes. Activation of the cAMP system was evaluated by measurements of the amount of cAMP released into the perfusion medium. T₄, T₃, calcitonin and somatostatin were measured by radioimmunoassays. 3 × 10^-6 M VIP induced increases in cAMP release and T₄ and T₃ secretion from the thyroid while there were no significant alterations in calcitonin and somatostatin release (n=4). In experiments employing both of the two isolated thyroid lobes 100 μU/ml TSH gave considerably higher increases in T₄ and T₃ secretion than 10^-6 M VIP (n=4). The effect of 10^-9M VIP on T₄ and T₃ secretion was similar to that of 10^-6M VIP (n=4). 10^-10M VIP induced a small but statistically significant increase in T₄ and T₃ secretion in two experiments while no effect was observed in two dogs.

This high sensitivity of the follicular cells to VIP and the demonstration by others of VIP containing nerves in the thyroid suggest that VIP-ergic nerves may be involved in the regulation of thyroid hormone secretion.

Key-Words

cAMP - Calcitonin - Somatostatin - Thyroxine - Triiodothyronine - Vasoactive Intestinal Peptide