TRH Immunoreactivity in Human Urine: Evidence for Dissociation from TRH

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Abstract
Affinity chromatography columns containing rabbit antiserum to thyrotropin releasing hormone (TRH) were prepared and used to concentrate and investigate human urinary TRH imrnunoreactivity (TRH-IR). The recovery of synthetic TRH, [3H]TRH, and [125I]TRH when added to 20 to 25 ml of urine was 33 ± 9% (mean ± SE), 35 ± 8%, and 36 ± 6%, respectively. Twenty-fivefold urine concentrates (UC) contained only 0.05% of the least amount of urea which would affect the TRH radioimmunoassay (RIA). RIA of the UC containing only endogenous TRH-IR indicated a value of 177 ± 35 pg/ml which corresponded to a calculated concentration inthe original urine of 35 ± 10 pg/ml, based on synthetic and labeled TRH recovery. Destruction of the endogenous TRH-IR of UC by incubation with human serum was similar (mean= 75% loss) to that of synthetic TRH (mean = 73% loss). Measurement of TRH-IR in UC utilizing two different anti-TRH sera resulted in significantly (P< 001) different values despite the fact that the two antisera measured the same amount of TRH-IR in a UC prepared from urine obtained following iv injection of syntheticTRH and in an extract of porcine stalk medium eminence. The pattern of TRH-IR of UC following Sephadex G–10 gel filtration was retarded as compared to synthetic or [3H]TRH. These results suggest that endogenous TRH-IR observed in human urine even afterconcentration by affinity chromatography is not TRH but is attributable to cross-reacting substance(s) whichare also susceptible to degradation by serum.