Abstract
The two peptides VIP (vasoactive intestinal peptide) and helodermin have both been shown to occur within the thyroid gland: VIP in intrathyroidal nerves and helodermin in the C-cells. Both peptides have previously been demonstrated to enhance the release of radioiodine from the prelabelled thyroid in vivo. Since a considerable amount of radioiodine released from the thyroid under these conditions may be non-hormonal, we reexamined the effects of VIP and helodermin on thyroid hormone secretion by the use of the specific technique of studying the release of radioiodine bound to specific T4 antiserum in mice. We thereby found that anti-T4-bound radioiodine in T3-pretreated animals increased after intravenous injection of VIP (1.5 nmol/animal) to 280 +/- 24% (P less than 0.001), and after intravenous injection of helodermin (1.5 nmol/-animal) to 186 +/- 26% (P less than 0.001) compared to 78 +/- 5% in controls. As a comparison, the corresponding figure after injection of TSH (70 microU/animal) was approximately 350% (P less than 0.001). In contrast, in animals not pretreated with T3, neither TSH, nor VIP helodermin significantly altered the plasma level of anti-T4-bound radioiodine. Also, VIP and helodermin did not change the plasma levels of free T4 in non-pretreated animals. In summary, the sensitive and specific technique of measuring the release of anti-T4-bound radioiodine in vivo after pretreatment with NA 125I and T3 detected a stimulation of the thyroid hormone secretion by VIP and helodermin.(ABSTRACT TRUNCATED AT 250 WORDS)
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