Circulating plasma cfactor-likeg immunoreactivity

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Abstract
Normal human peripheral plasma, examined by direct radioimmunoassay corticotrophin-releasing factor (CRF) using seven different antisera, showed marked inhibition of tracer binding to antiserum. This apparently high Cimmunoreactiv(CRF-LI) dilute in parallel with synthetic human CRF-41.parison, most equine and ovine plasma samples had low Cconcentrations.ractionation of both normal and late pregnancy human plasma on SG-75 neutral pH indicated the majority of the CRF-LI of large molecular size. The molecular weight was estimated to be approximately 29 000 following chromatography human plasma on Sephacryl S-200.igh CRF-LIrmal plasma was reduced to barely detectable levels by methanol treatment despite the recovery of added human CRF-41 of >80%. Methanol extracts of late pregnancy human plasma, however, retained high CRF-LI which exhibited the immunoreactive and Sephadex elution characteristics of synthetic human CRF-41. 125I-Labelled human CRF-41 added to human plasma showed a reversible, time-dependent alteration in molecular size and reduction in binding to excess antiserum. These findings indicate that direct RIA of human CRF in unextracted plasma leads to spurious results and suggest the presence in human plasma of an interfering factor and/or binding substance that is not generally apparent in equine or ovine plasma under the conditions described. J. Endocr. (1988) 117, 299–307