Alterations of carboxypeptidases N activities in patients with thyroid dysfunction

Serum carboxypeptidases N (EC. 3.4.17.3) were determined spectrophotometrically in 87 patients with disturbances of thyroid function and in 131 euthyroid individuals, including 33 women taking estrogens for contraception. Carboxypeptidases N (CN) can be subdivided into CN1 and CN2, according to variable substrate affinity. In addition, measurements of blood pressure and in vitro tests of thyroid function were performed. In euthyroid controls, CN1 was negatively correlated with age. No significant differences between CN1 and CN2 have been observed with regard to sex. In patients with hyperthyroidism, the mean values of both enzymes were elevated, but this tendency proved to be significant only for CN2. In hypothyroid patients CN1 and CN2 levels were normal. Elevations of CN1 and CN2 in the hyperthyroid state seem not to be related to underlying immunological processes but to the thyroid hormone excess itself. In euthyroid women taking estrogens for contraception CN2 was also elevated.