Chen T C, Weber M A
Clin Chim Acta. 1980 Nov 6;107(3):217-22. doi: 10.1016/0009-8981(80)90449-0.
Since the protease inhibitor, di-isopropylfluorophosphate (DFP), inhibits the cryoactivation of inactive renin, its addition to stored plasma should prevent unintended renin activation and thereby minimize this source of inaccuracy in the assay of plasma renin activity. However, we have found that 6 mmol/l DFP in stored frozen plasma actually reduced plasma renin activity from 4.89 +/- 0.13 (S.D.) to 2.48 +/- 0.17 ng . ml-1 . h-1 (p < 0.001). This effect did not occur if DFP was added immediately before assay, suggesting that the decreased renin activity reflected an action of DFP on components of the renin system during storage rather than any interference with the assay method itself. The organic solvent isopropanol, which is required to dilute the DFP, appeared responsible for this phenomenon, for when the isopropanol alone, in concentrations of 20 and 40 microliter/ml, was added to stored frozen plasma it decreased plasma renin activity from 3.6 +/- 0.3 to 2.2 +/- 0.1 and 0.6 +/- 0.1 ng . ml-1 . h-1, respectively (p < 0.001 in each case). Correspondingly, plasma renin substrate concentrations were decreased to 71% and 6% of control, indicating that the renin activity reductions produced by isopropanol were due to its denaturation of substrate. Moreover, addition of exogenous sheep renin substrate (1400 ng/ml) immediately before assay restored plasma renin activity to control. Thus, although DFP effectively prevents inadvertent renin activation in stored frozen plasma, it would seem important that subsequent assays for plasma renin activity be performed in the presence of added exogenous substrate.
由于蛋白酶抑制剂二异丙基氟磷酸酯（DFP）可抑制无活性肾素的低温激活，因此在储存的血浆中添加该抑制剂应可防止意外的肾素激活，从而将血浆肾素活性测定中这一误差来源降至最低。然而，我们发现，在储存的冷冻血浆中加入6 mmol/l的DFP后，血浆肾素活性实际上从4.89±0.13（标准差）降至2.48±0.17 ng·ml⁻¹·h⁻¹（p<0.001）。如果在测定前立即加入DFP，则不会出现这种效应，这表明肾素活性降低反映了DFP在储存期间对肾素系统成分的作用，而非对测定方法本身的任何干扰。用于稀释DFP的有机溶剂异丙醇似乎是造成这一现象的原因，因为当单独将浓度为20和40微升/毫升的异丙醇加入储存的冷冻血浆中时，血浆肾素活性分别从3.6±0.3降至2.2±0.1和0.6±0.1 ng·ml⁻¹·h⁻¹（每种情况p<0.001）。相应地，血浆肾素底物浓度降至对照的71%和6%，表明异丙醇导致的肾素活性降低是由于其使底物变性。此外，在测定前立即加入外源性绵羊肾素底物（1400 ng/ml）可使血浆肾素活性恢复至对照水平。因此，尽管DFP可有效防止储存的冷冻血浆中肾素的意外激活，但在随后的血浆肾素活性测定中加入外源性底物似乎很重要。
