Diurnal variation of the human urinary TRH excretion measured by radioimmunoassay

Urine TRH was estimated by the radioimmunoassay which was accomplished according to the method of Bassiri and Utiger. Minimum detectable dose of TRH was 25 pg and recovery of TRH ranged from 72% to 112% in our laboratory. Intraassay coefficients of variation were 5.4% to 14.0% and interassay variations were 10.6% to 15.0%. Of the TRH analogues tested, only two (Ser-His-Pro-NH2, Thr-His-Pro-NH2) had potent reactivity to anti-TRH serum in large dose of 100 ng/tube. Urine samples were kept at -20 degrees C after adjusted to pH 3.0 because the inactivation of TRH in urine was markedly dependent on temperature and pH value. Using this radioimmunoassay, diurnal variation of the urinary TRH excretion at regular intervals in normal subjects was observed. Peak TRH excretion occurred around early morning, while minimum of the excretion was observed around noon. Total urinary TRH excretion of 24 hours was 817-1579 ng (M+/-SE: 1241+/-89 ng) in normal subjects. In patients with chronic renal failure, urinary excretions of TRH was obviously lower than those of normal subjects.