Stimulatory action of pituitary adenylate cyclase-activating polypeptide (PACAP) on thyroid gland

PACAP 27 and 38 (27 and 38 amino acids, respectively) increased rapidly cAMP production in porcine thyroid cells in vitro. Both PACAPs also increased T4 production from mouse thyroid in vivo similar to TSH. Both PACAPs (especially 38) inhibited the binding of 125I-labeled TSH to thyroid membrane in the medium containing bovine serum albumin. This inhibitory action remarkably decreased in the medium containing normal human serum. Decrease of inhibition of TSH binding by serum containing PACAP could not be explained simply by proteolytic destruction of PACAP, although the labeled PACAP (especially 38) was destructed by proteases in thyroid membrane or human serum. These facts showed that PACAP had the thyroid stimulating action and the inhibitory action on the binding of TSH to thyroid receptor.