A kinetic study on secretion and elimination of endogenous thyrotropin in the thyrotropin-releasing hormone test

Pulsatile secretion of thyrotropin in children

To examine pulsatile TSH secretion, serum TSH was determined every 30 min for 24 h in eight short normal prepubertal children (3 males and 5 females, age 4.0-12.6 yr). All children exhibited a clear circadian pattern of TSH secretion. Pulsatile TSH secretion was identified in all subjects with a mean (+/- SD) TSH pulse frequency of 6.9 +/- 1.2 pulses/24 h. The group mean TSH pulse amplitude was 1.4 +/- 0.3 mU/L. Mean TSH concentration was higher during the night hours (2.1 +/- 0.8 mU/L) than during the day hours (1.3 +/- 0.4 mU/L, p < 0.005), and significantly more pulses were detected during the night (mean 4.7 +/- 1.4) than during the day hours (2.1 +/- 0.6, p < 0.005). On average, 62 to 68% of the peaks were detected in the night hours. Mean TSH pulse amplitude during the night hours was not significantly different from that during the day hours. Our findings indicate that, as previously shown in adults, a pulsatile pattern of TSH secretion is present in children. In our study group, the nocturnal TSH surge is associated with an increase in pulse frequency but not amplitude.