Plasma neuropeptides in hyperthyroidism.

Plasma levels of the neuropeptides, vasoactive intestinal polypeptide (VIP, neuropeptide Y (NPY), calcitonin gene-related peptide (CGRP), substance P, and galanin were determined in 15 hyperthyroid patients before and at 3 occassions during 38 weeks of treatment. Treatment was performed with either 131I alone or with carbimazole, with combination of carbimazole and thyroxine, or with subtotal thyroidectomy. Before and after 11 (+/- 4), 24 (+/- 6) and 38 (+/- 5) weeks of treatment, plasma neuropeptide levels were analysed. A group of 9 premenopausal women served as controls. During hyperthyroidism, mean plasma level of CGRP was higher than in controls (P less than 0.001). In contrast, the mean plasma levels of the other measured neuropeptides did not differ from those in the controls. Mean serum level of tree T4 was lowered from 81.9 +/- 30.1 to 23.9 +/- 8.6 pmol/l and mean serum level of free T3 was lowered from 27.3 +/- 7.9 to 6.7 +/- 2.3 pmol/l during the course of the treatment. After 11 weeks of treatment, mean plasma NPY level was significantly increased (P = 0.004) compared to pretreatment levels. However, after 38 weeks of treatment, mean plasma NPY level had returned to control values. The mean plasma CGRP level was significantly reduced at 11 and 38 weeks of treatment compared to pre-treatment value (P = 0.002 and P = 0.004, respectively). Mean plasma level of neurotensin slowly declined during the treatment (P = 0.003). In contrast, mean plasma level of VIP, of substance P, and of galanin did not differ from control value before or after treatment.(ABSTRACT TRUNCATED AT 250 WORDS)