[Studies of various factors in thyrotropoin releasing hromone TRH) radioimmunoassay for serum (author's transl)]

Abstract

To study the significance of TRH in the hypothalamo-pituitary-thyroid axis measurement of TRH in body fluid are needed. We previously reported TRH radioimmunoassay for urine. TRH radioimmunoassay for serum has not established yet, because TRH immunoreactivity is inactivated with serum. We investigated effects of various factors on this inactivation and method for prevention of this inactivation. Synthetic TRH was added to normal human serum at 4 degrees C and incubated at 60 degrees C, 37 degrees C, 20 degrees C, 4 degrees C or -20 degrees C for various intervals. After incubation, recovery of TRH was measured. After one hour incubation, recovery of TRH was 9.2% at 37 degrees C, 34.5% at 20 degrees C, 100% at 4 degrees C or -20 degrees C. Incubation of TRH serum mixtures at 65 degrees C after incubation at 37 degrees C resulted in some recovery of TRH. After one hour incubation at 37 degrees C, recovery of TRH was 9.2% at serum pH 7.0, 100% at serum pH 3.0 to 5.0 or 11.0. Recovery of TRH was increased in accordance with stepwisely increase of serum dilution. Concentrations of serum thyroid hormone did not affect recovery of TRH. Smaller quantities of TRH were more rapidly inactivated. Inactivation of TRH immunoreactivity could be prevented addition of BAL (over 0.25 mg/ml) or mixture of 8-Hydroxyquinoline (HQ) and Tween 20(T) (over 0.1 mg/ml of HQ and 1 lmg/ml of T). Duration of effectiveness of BAL was short. Effectiveness of HQT continued for 12 weeks, if HQT treated serum was stored at -20 degrees C. From above data it was suggested that TRH immunoreactivity might be inactivated with enzyme system and other factors and TRH levels in the serum might be able to measure with addition of HQT to serum.