[Radioimmunoassay of plasma calcitonin gene-related peptide (CGRP) levels in patients with endocrine tumor].

For the purpose of determining the significance of CGRP for endocrine tumors, we attempted to establish CGRP radioimmunoassay (RIA) system and to measure plasma CGRP levels in patients with endocrine tumor. One ml of plasma (EDTA-2K + aprotinin 500.KIE/ml) was applied to Sep-Pak C 18 column, and was eluted by 90% MeOH plus 0.1% TFA. The eluted samples were used for RIA. RIA was performed by two day-one day system (delayed assay). B/F separation was made by two Ab-PEG method. Cross-reactivity of antisera was 0.0025% and below 0.0001% against PTH and calcitonin in human, respectively. The standard curve of CGRP showed a dose response curve. Results of dilution and reproduction tests were excellent. Normal range of serum CGRP was 6.7 +/- 3.0 pg/ml (M +/- SD) and the cut-off level was determined to be 12.7 pg/ml. Plasma CGRP showed 128,323 and 2,010 pg/ml in three preoperative patients with medullary thyroid carcinoma, indicating extremely high levels. On the other hand, plasma CGRP levels increased in 2/7, 2/4, 2/5, and 0/3 in patients with parathyroid adenoma, benign insulinoma, carcinoid and pheochromocytoma, respectively. Correlation between CGRP level and calcitonin levels was significant (r = 0.789) in only 16 patients with medullary thyroid carcinoma. This study suggests that our CGRP RIA system was satisfactory for clinical use and measurement of CGRP may be potentially useful for clearing the pathophysiology of neuroendocrine tumors, although CGRP level was raised in patients with medullary thyroid carcinoma.