Key result
Specific radioimmunoassay detects high ANP levels in eel atrium and plasma, primarily as ANP-1-27.
A highly specific radioimmunoassay was developed to measure eel ANP, revealing high concentrations in the eel atrium and plasma compared to mammals.
Eel ANP data should not alter human diagnostics; extends natriuretic peptide characterization to teleosts.
A highly specific and sensitive radioimmunoassay has been developed for the measurement of eel atrial natriuretic peptide (ANP). The antiserum, raised against eel ANP-(1-27) did not cross-react with two other eel natriuretic peptides, i.e. eel ventricular natriuretic peptide and C-type natriuretic peptide (CNP), or with any mammalian ANPs, CNPs or brain natriuretic peptides so far identified. The minimal detectable amount was 0.39 fmol (0.90 pg)/tube with more than 99% confidence. Because of its high sensitivity, the radioimmunoassay makes it possible to measure eel ANP directly with only a few microlitres of plasma without extraction. Using the radioimmunoassay we found high levels of ANP in the atrium (11 +/- 2 pmol/mg wet tissue, n = 8), and much lower levels in the ventricle (56 +/- 8 fmol/mg, n = 8) and the brain (22 +/- 1 fmol/mg, n = 8) of eels. Eel plasma contained a large amount of ANP (247 +/- 66 fmol/ml, n = 8) compared with the levels reported in mammals, although atrial levels are similar between eels and mammals. Gel-permeation chromography revealed that a major form of ANP stored in the eel atrium, ventricle and brain has a molecular mass of approximately 14 kDa but low molecular forms of about 3 kDa are predominant in eel plasma. A detailed analysis with reverse-phase high-performance liquid chromatography showed that a major molecular form circulating in eel plasma is ANP-(1-27). ANP-(1-27) was also detected in small amounts in the eel atrium, ventricle and brain.
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Takei et al. (1992) studied this question. Radioimmunoassay for eel atrial natriuretic peptide was evaluated on ANP levels in eel tissues and plasma. A highly specific radioimmunoassay detected high levels of ANP in the eel atrium (11 pmol/mg) and plasma (247 fmol/ml), with the major circulating form being ANP-(1-27).
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