Pyroglutamyl peptidase-II ("thyroliberinase") activity in human serum: Influence of weight and thyroid status

Theodore C. Friedman, Jack A. Yanovski, Vachareeporn Jayasvasti, Susan Z. Yanovski, Ronald J. Koenig, Sherwin Wilk

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17 Scopus citations


The tripeptide hormone, TRH, is metabolized by three enzymes, the most specific of which is pyrogiutamyl peptide hydrolase-II (also termed thyroliberinase), a metalloenzyme present in serum and brain. Because pyrogiutamyl peptidase-II activity in rat serum is regulated by thyroid hormone levels, we tested the hypothesis that this activity is similarly altered in humans. We studied serum pyroglutamyl peptidase-II activity in 6 patients with hyperthyroidism, 18 patients with hypothyroidism, and 31 euthyroid, normal weight volunteers. Because TRH [or its metabolite cyclo(His-Pro)] is believed to be an important hormone regulating appetite and metabolism, we also evaluated pyroglutamyl peptidase-II activity in 27 euthyroid patients with obesity. Serum pyrogiutamyl peptidase-II activity was elevated in patients with hypothyroidism (mean ± SEM, 33.9 ± 3.7 nmol/mL·h) compared to that in euthyroid, normal weight volunteers (24.5 ± 2.8 nmol/mL·h; P < 0.05), but not that in patients with hyperthyroidism (28.3 ± 4.1 nmol/mL·h; P = NS). Euthyroid obese patients had the highest pyroglutamyl peptidase-II activity (43.6 ± 2.8 nmol/mL·h; P < 0.0001 vs. normal weight volunteers). Pyroglutamyl peptidase-II activity was positively correlated with body mass index (r2 = 0.30; P < 0.0001). After correction for body mass index, there were no difference in pyroglutamyl peptidase-II activity in hypothyroid, hyperthyroid, and euthyroid individuals. We conclude that serum pyroglutamyl peptidase-II activity is regulated by, or regulates, body weight.

Original languageEnglish
Pages (from-to)1086-1089
Number of pages4
JournalJournal of Clinical Endocrinology and Metabolism
Issue number4
StatePublished - Apr 1995


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