Generation of prostaglandin E2-like radioimmunoreactive material in human plasma during storage at -20 C but not at -80 C.
Concentrations of prostaglandin E2 (PGE2) as determined by radioimmunoassay following silicic-acid column chromatography in extracted samples (n = 5) of human plasma (Na2EDTA: 18 mg/5 ml blood; indomethacin: 1mg/5 ml blood) were less than 1.0 pg/ml when the samples were extracted immediately after blood withdrawal. Virtually identical concentrations of PGE2 were determined in samples stored at -80 degrees C for up to 6 months. However, when the same analytical procedures were used after prolonged storage of the plasma samples at -20 degrees C an apparent rise in the estimated plasma concentrations of PGE2 up to 5.1 +/- 1.9 pg/ml (3 months) and to 25.2 +/- 7.8 pg/ml, (6 months) was observed. Repeated freezing and rethawing of 4 plasma samples within 48 hours after blood withdrawal did not influence concentrations of PGE2 thus excluding acute destruction of residual platelets as the cause of the observed time-dependent rise in radioimmunologically determined 'PGE2'. Two plasma samples stored at -20 degrees C for 26 months were subjected to HPLC subsequent to silicic acid column chromatography. Radioimmunoassay of PGE2 performed for each eluted fraction resulted in 3 distinct peaks of "PGE2"-like activity, suggesting heterogeneity of cross-reacting compounds generated during prolonged storage at -20 degrees C. In conclusion, to determine concentrations of PGE2 in human plasma by means of radioimmunoassay the samples should either be extracted immediately after blood withdrawal or be kept at -80 degrees C.
D000328:Adult; D015232:Dinoprostone; D005615:Freezing; D006801:Humans; D008297:Male; D008875:Middle Aged; D011458:Prostaglandins E / Q000097:blood*; D011863:Radioimmunoassay
D011458:Prostaglandins E; D015232:Dinoprostone