IMMUNIZATION AGAINST VASOACTIVE-INTESTINAL-PEPTIDE DOES NOT AFFECT THYROID-HORMONE SECRETION OR THYROID BLOOD-FLOW

Vasoactive intestinal peptide (VIP) is present in thyroid parasympathe tic nerves. To assess the involvement of endogenous VIP in the regulat ion of thyroid function, blood levels of thyroid hormones and thyroid blood flows (TBF) were measured after systemic immunization against VI P or after transection of the superior laryngeal nerves in male rats, which reduced the thyroid content of VIP but did not affect blood leve ls of thyroid hormones or TBF. Anti-VIP monoclonal antibody or anti-VI P serum was used for immunization against VIP in normal rats. In addit ion, VIP antibody was given to rats fed an iodine-deficient diet for 5 days to examine the involvement of this peptide in iodine deficiency- induced increases in TBF. Effects were measured at different times (90 s, 30 min, 1 h, and 5 days) after immunoneutralization, but none of t hese treatments changed blood levels of thyroid hormones or TBF in nor mal or iodine-deficient rats. However, passive immunization against VI P was associated with a high binding capacity of rat plasma to VIP, an d this treatment reduced blood levels of prolactin as well as blood fl ows to the duodenum, stomach, and lung. These findings suggest that th e VIP present in thyroid nerves is not involved in maintaining basal t hyroid hormone secretion or TBF and that this neuropeptide does not me diate thyroid vascular adjustments to dietary iodine deficiency.