Shalmi M, Lunau H E, Petersen J S, Bak M, Christensen S
Department of Pharmacology, University of Copenhagen, Denmark.
Am J Physiol. 1991 Feb;260(2 Pt 2):F283-9. doi: 10.1152/ajprenal.1991.260.2.F283.
Purity of different batches of [3H]inulin delivered from leading manufacturers was elevated with a chromatographic method (Sephadex G-25 column) that allowed simultaneous analysis of cold inulin, [3H]inulin, and [14C]inulin in the same run. Among four batches of [3H]inulin received within 5 mo, two were found relatively pure, whereas two were partly decomposed to lower-molecular-weight fragments. The chromatographic profile of pure isotopes was not significantly affected by redistribution and freeze drying, nor by subsequent storage in the freeze-dried state at -20 degrees C for up to 5 mo, nor by incubation in aqueous solution at 37 degrees C for 24 h. Three batches of [3H]inulin with different grades of decomposition (noninulin percentages 13%, 38%, and 61%, respectively) were selected for clearance experiments and infused simultaneously with cold and undecomposed [14C]inulin to conscious rats. [14C]inulin had a significantly higher clearance than cold inulin (+7.6 +/- 0.6%) and relatively pure [3H]inulin (+12.4 +/- 0.4%). Decomposed [3H]inulin isotopes progressively underestimated clearance of cold inulin to an extent related to the degree of decomposition. Thus at the end of the 5-h clearance experiment, ratios between clearance of tracer and of cold inulin were 0.92, 0.71, and 0.60 for the three 3H isotopes, respectively. This study indicates that [3H]inulin delivered from leading manufacturers may be decomposed to an extent that invalidates its use as a marker for glomerular filtration rate (GFR). It is thus necessary to check the purity routinely before use. Within the same rat, clearance of undecomposed [3H]inulin and [14C]inulin may differ by 12%, and for this reason they should not be used interchangeably as GFR markers.
采用一种色谱方法（葡聚糖凝胶G - 25柱）提高了主要制造商提供的不同批次[³H]菊粉的纯度，该方法能在同一次运行中同时分析冷菊粉、[³H]菊粉和[¹⁴C]菊粉。在5个月内收到的四批[³H]菊粉中，发现两批相对纯净，而另外两批部分分解为低分子量片段。纯同位素的色谱图谱不受再分配、冷冻干燥的显著影响，也不受随后在-20℃冷冻干燥状态下储存长达5个月的影响，也不受在37℃水溶液中孵育24小时的影响。选择三批分解程度不同（非菊粉百分比分别为13%、38%和61%）的[³H]菊粉进行清除实验，并与冷的未分解的[¹⁴C]菊粉同时注入清醒大鼠体内。[¹⁴C]菊粉的清除率明显高于冷菊粉（+7.6±0.6%）和相对纯净的[³H]菊粉（+12.4±0.4%）。分解的[³H]菊粉同位素逐渐低估了冷菊粉的清除率，低估程度与分解程度有关。因此，在5小时清除实验结束时，三种³H同位素的示踪剂清除率与冷菊粉清除率的比值分别为0.92、0.71和0.60。这项研究表明，主要制造商提供的[³H]菊粉可能分解到一定程度，使其作为肾小球滤过率（GFR）标志物的用途无效。因此，在使用前必须常规检查其纯度。在同一只大鼠体内，未分解的[³H]菊粉和[¹⁴C]菊粉的清除率可能相差12%，因此它们不应作为GFR标志物相互替代使用。
