title: Radioimmunoassay of cyclo(His-Pro) in unextracted human plasma: report of a normal range and definition of factors critical for successful assay.
abstract: A radioimmunoassay for cyclo(His-Pro) (CHP) in unextracted human plasma that can detect 40 pg has been developed. Elution profile of CHP-like immunoreactivity (CHP-LI) corresponded precisely to those of [3H] cyclo(His-Pro) by both high pressure liquid chromatography and Sephadex G-25 column chromatography. In addition plasma CHP-LI exhibited close immunoidentity with authentic CHP. Charcoal treatment of plasma containing [3H] cyclo(His-Pro) resulted in loss of both CHP-LI and [3H] cyclo(His-Pro) activity. Plasma frozen at draw and assayed at 0, 6 and 24 hours displayed no change in CHP-LI while an aliquot from the same sample maintained at 4 degrees C and assayed at the same time intervals showed a 50% rise (0 hrs-856 +/- 47 pg/ml; 24 hrs-1288 +/- 85 pg/ml) (+/- SE) over 24 hours. In addition, plasma drawn from 14 volunteers and immediately frozen until assay yielded a mean CHP value of 829 +/- 64 pg/ml (+/- SE) while that of 14 volunteers that was maintained at 25 degrees C for 90 minutes was significantly higher at 1085 +/- 34 pg/ml (+/- SE) (p less than 0.03). Taken together, these data suggest that CHP can be easily measured in a direct RIA of human plasma, however, failure to maintain the sample frozen from the time of draw until assay may yield spuriously elevated values.
authors.affiliation: Department of Medicine, LSU Medical Center, New Orleans 70112.
authors.forename: C W
authors.initials: CW
authors.lastname: Hilton
authors.forename: C
authors.initials: C
authors.lastname: Prasad
authors.forename: J F
authors.initials: JF
authors.lastname: Wilber
authors.forename: G C
authors.initials: GC
authors.lastname: Wolf
authors.forename: D
authors.initials: D
authors.lastname: Rogers
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D010456:Peptides, Cyclic / Q000097:blood*; D010879:Piperazines / Q000097:blood*; D011863:Radioimmunoassay; D013048:Specimen Handling
chemical_list: D010456:Peptides, Cyclic; D010879:Piperazines; C015924:histidyl-proline diketopiperazine