Radioimmunoassay for TA-0910, a new stable thyrotropin releasing hormone analogue and its metabolite, TA-0910 acid-type, in human plasma and urine.

Radioimmunoassay (RIA) was investigated for the determination of TA-0910 and its main metabolite, TA-0910 acid-type, in human plasma and urine. TA-0910 is a new metabolically stable analogue of thyrotropin releasing hormone (TRH). Antiserum was raised in the rabbit against the 1-fluoro-2,4-dinitrophenyl derivative of TA-0910 or TA-0910 acid-type conjugated to keyhole limpet hemocyanin (KLH). The radioligand was prepared by iodination with 125I of the histidine imidazole ring of TA-0910 or TA-0910 acid-type. Cross-reactivities of anti-TA-0910 or TA-0910 acid-type antiserum for TA-0910, its metabolite and related compounds were low. The calibration range was 0.02-5 ng ml-1 using 100 microliters human plasma or urine. Inter-day variations of TA-0910 and TA-0910 acid-type assay in plasma were 3.5-15.5 and 1.8-9.4%, respectively. The variations of the assay in urine were the same as those in plasma. The recovery of TA-0910 and TA-0910 acid-type spiked in plasma or urine samples was approximately 100%. Furthermore, this method was applied to the determination of TA-0910 and TA-0910 acid-type in human plasma and urine samples, for the evaluation of the pharmacokinetics of TA-0910 in humans. From the results it was demonstrated that he developed RIA was useful for the determination of TA-0910 and TA-0910 acid-type in human plasma and urine, and was applicable to pharmacokinetic studies in humans.