Elastase inhibitory activity in serum of patients with thyroid dysfunction.

Dermal elastic fiber fragmentation and decreased fiber density are characteristic cutaneous abnormalities in myxedema. We therefore evaluated elastase inhibitory activity in serum in thyroid dysfunctional states by measuring the protease inhibitor alpha 1-antitrypsin (A-1-AT), as well as by directly determining the inhibition of porcine pancreatic elastase activity. Overall there was a strong correlation between A-1-AT concentration and elastase inhibitory activity in serum (r = 0.95, P less than 0.001). Mean (+/- SE) A-1-AT concentrations were greatest in hyperthyroidism (39 +/- 3 mumol/L, n = 13), followed by normal controls (29 +/- 1, n = 11), subclinical hypothyroidism (27 +/- 2, n = 7), and hypothyroidism (25 +/- 1, n = 12). Concentrations of both A-1-AT and porcine pancreatic elastase inhibitory activity were significantly greater in subjects with hyperthyroidism than in the other groups (P less than 0.01). The correlations (r) between the overall free thyroxin (T4) index and A-1-AT and elastase inhibitory activity were 0.68 and 0.61, respectively (P less than 0.01), implying that free T4 variations account for 46% of the variance in A-1-AT concentrations and 37% of the variance in elastase inhibitory activity. We conclude that serum elastase inhibitory activity is increased in hyperthyroid patients.