Pyroglutamyl peptidase-II ("thyroliberinase") activity in human serum: influence of weight and thyroid status.
The tripeptide hormone, TRH, is metabolized by three enzymes, the most specific of which is pyroglutamyl peptide hydrolase-II (also termed thyroliberinase), a metalloenzyme present in serum and brain. Because pyroglutamyl 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 pyroglutamyl 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.
Friedman
T C
TC
Laboratory of Developmental Neurobiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
Yanovski
J A
JA
Jayasvasti
V
V
Yanovski
S Z
SZ
Koenig
R J
RJ
Wilk
S
S
D000328:Adult; D000626:Aminopeptidases / Q000097:blood*; D015992:Body Mass Index; D001835:Body Weight; D005260:Female; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood*; D007037:Hypothyroidism / Q000097:blood*; D008297:Male; D009765:Obesity / Q000097:blood; D011761:Pyrrolidonecarboxylic Acid / Q000031:analogs & derivatives; D012016:Reference Values
D000626:Aminopeptidases; C023166:pyroglutamyl-peptidase II; D011761:Pyrrolidonecarboxylic Acid