To extract or not to extract in secretin radioimmunoassay?
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The importance of an ethanol extraction procedure in the radioimmunoassay of plasma secretin was investigated. The extraction step led to a higher assay sensitivity of 0.35 fmol/ml, compared to 5.93 fmol/ml using unextracted samples. The rise of plasma secretin after infusion of a low dose of secretin (1 pmol·kg−1·h−1) in 10 healthy humans was only detected after sample extraction. Higher doses (3 and 9 pmol·kg−1·h−1) resulted in increments of plasma IRS (immunoreactive secretin), which could be recorded both with and without sample extraction. After a steak meal 7 of 10 subjects showed a significant increase of plasma secretin assaying extracted plasma samples. The secretin release occurred in spikes. The mean increase of plasma IRS in this group was 0.6 fmol/ml, the mean maximal secretin release above basal was 2.3 fmol/ml. Without sample extraction, plasma secretin was not significantly changed. We conclude that plasma samples should be extracted in order to detect physiological postprandial secretin release.
Key wordsSecretion radioimmunoassay Ethanol extraction humans
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