Pemberton C J, Yandle T G, Rademaker M T, Charles C J, Aitken G D, Espiner E A
Department of Endocrinology, Christchurch School of Medicine, Christchurch 1, New Zealand.
Am J Physiol. 1998 Oct;275(4):H1200-8. doi: 10.1152/ajpheart.1998.275.4.H1200.
We have recently identified a novel amino-terminal fragment of pro-brain natriuretic peptide (NT-proBNP) in the circulation of humans, the concentration of which increases progressively as the left ventricle fails. To clarify the origins of NT-proBNP in experimental animals, we have developed an RIA for NT-proBNP based on residues 52-71 of ovine proBNP-(1-103) and used it to study cardiac processing, secretion, and metabolism of BNP in sheep with cardiac overload induced by coronary artery ligation (CAL) or rapid left ventricular pacing (rLVP). The concentration of NT-proBNP in left atrial plasma extracts drawn from normal control sheep was threefold that of mature BNP. Size-exclusion and reverse-phase HPLC analyses of plasma extracts coupled to RIA revealed a single peak of immunoreactive (ir) NT-proBNP [ approximately 8,000 relative molecular weight (Mr)], quite distinct from a single peak of ir-mature BNP ( approximately 3,000 Mr). In contrast, ovine cardiac tissue contained only a single immunoreactive peak of high-molecular-weight BNP ( approximately 11,000 Mr), consistent in size with proBNP-(1-103). Sampling from the cardiac coronary sinus in normal control sheep (n = 5) and sheep with CAL (n = 5) revealed that the molar ratio of NT-proBNP to mature BNP was similar. There was a significant gradient of both mature and NT-proBNP across the heart in normal sheep, whereas after CAL the gradient was significant for mature BNP only. In both forms of cardiac overload (CAL and rLVP), left atrial plasma levels of NT-proBNP were significantly increased above normal levels, in contrast with mature BNP levels, which were raised only in the rLVP group of animals. Blockade of natriuretic peptide metabolism in sheep with heart failure (induced by rLVP) raised mature BNP levels threefold but did not affect levels of NT-proBNP. In conclusion, these studies show that NT-proBNP is formed from proBNP stores during secretion and, compared with mature BNP, accumulates in plasma because metabolism of NT-proBNP appears to differ from that of mature BNP. Although its function, if any, remains unclear, plasma NT-proBNP may prove to be a sensitive marker of cardiac overload and/or decompensation.
我们最近在人类血液循环中发现了一种新型的脑钠肽原（NT-proBNP）氨基末端片段，其浓度随着左心室功能衰竭而逐渐升高。为了阐明实验动物体内NT-proBNP的来源，我们基于绵羊脑钠肽原（1-103）的52-71位氨基酸残基开发了一种NT-proBNP放射免疫分析法（RIA），并用于研究冠状动脉结扎（CAL）或快速左心室起搏（rLVP）诱导的心脏负荷过重绵羊体内BNP的心脏加工、分泌及代谢情况。从正常对照绵羊抽取的左心房血浆提取物中，NT-proBNP的浓度是成熟BNP浓度的三倍。将血浆提取物进行尺寸排阻和反相高效液相色谱分析并结合RIA检测，结果显示免疫反应性（ir）NT-proBNP有一个单一峰（相对分子质量约为8000），与ir-成熟BNP的单一峰（约3000）明显不同。相比之下，绵羊心脏组织仅含有一个高分子量BNP的免疫反应性峰（约11000），其大小与脑钠肽原（1-103）一致。对正常对照绵羊（n = 5）和CAL绵羊（n = 5）的心脏冠状窦进行采样，结果显示NT-proBNP与成熟BNP的摩尔比相似。正常绵羊心脏中成熟BNP和NT-proBNP均存在显著梯度，而CAL后仅成熟BNP存在显著梯度。在两种形式的心脏负荷过重（CAL和rLVP）中，NT-proBNP的左心房血浆水平均显著高于正常水平，与之形成对比的是，成熟BNP水平仅在rLVP组动物中升高。对心力衰竭绵羊（由rLVP诱导）的利钠肽代谢进行阻断，使成熟BNP水平升高了三倍，但未影响NT-proBNP水平。总之，这些研究表明NT-proBNP是在分泌过程中由脑钠肽原储存形成的，与成熟BNP相比，其在血浆中积累是因为NT-proBNP的代谢似乎与成熟BNP不同。尽管其功能（如果有）尚不清楚，但血浆NT-proBNP可能被证明是心脏负荷过重和/或失代偿的敏感标志物。
