Roffe C, MacDiarmaid-Gordon A, Ohanian V, Hollis S, Heagerty A M
Department of Medicine, University of Manchester, Hope Hospital, Salford, UK.
Cardiovasc Res. 1996 Jun;31(6):907-16.
The proto-oncogenes c-fos, c-myc and H-ras have been shown to rise in a characteristic pattern in the left ventricle undergoing hypertrophy in the coarctation model of experimental hypertension and there is some evidence to suggest that they might play a role in the initiation of hypertrophic growth. However, in vivo studies do not discriminate between the direct effects of pressure and pressure-independent trophic stimuli such as angiotensin II. To examine these influences separately we studied isolated working hearts exposed to different afterloads in the presence or absence of angiotensin II.
Hearts from normotensive female Wistar rats were perfused with a modified Krebs-Henseleit solution, with and without angiotensin II (100 nmol/1) and exposed to low (60 mmHg) or high (140 mmHg) afterload (n > 17/group). Proto-oncogene mRNA induction in the left ventricle was assessed by Northern blot analysis.
Aortic pressures were 101 +/- 14/63 +/- 6 mmHg (mean +/- s.d.) with low and 175 +/- 13/93 +/- 20 mmHg with high afterload; hearts in both groups maintained a stable cardiac output over 240 min, except for high afterload hearts not perfused with angiotensin II, which showed a 59% drop by the end of the experiment (P < 0.001). There was a 50% (32%, 72%) (geometric mean and 95% confidence interval) increase of c-myc and 54% (27%, 86%) increase in c-fos, but a 32% (25%, 40%) suppression of H-ras with high (140 mmHg) as compared with low (60 mmHg) afterloads (P < 0.0001 for each). There was no significant difference in c-myc and c-fos induction with different levels of high afterload (110, 120, 140 mmHg), but for H-ras suppression progressively increased with increasing afterload (P = 0.003). At high afterload, levels of c-fos rose at 30 min and peaked at 60 min, c-myc continued to rise up to 240 min, and H-ras was suppressed at all four time points. The addition of angiotensin II (100 nmol/l) to the perfusate resulted in 18% (6%, 28%; P = 0.006) lower c-myc levels, 12% (-6%, 28%; P = 0.18) lower c-fos levels and an 11% (-0.1%, 24%; P = 0.056) increase of H-ras.
The isolated perfused working rat heart is capable of performing stably for a period of at least 240 min at high afterload pressures comparable to those encountered in hypertension. A proto-oncogene induction similar to that seen in the hypertrophying heart can be induced by increased pressure alone, without the mediating effects of circulating angiotensin II. Hearts perfused with angiotensin II showed a more stable performance at high levels of afterload which was associated with a minor attenuation of pressure-induced changes in proto-oncogene expression.
原癌基因c-fos、c-myc和H-ras在实验性高血压缩窄模型中发生肥厚的左心室呈现出特征性的升高模式，并且有证据表明它们可能在肥厚性生长的起始中发挥作用。然而，体内研究无法区分压力的直接作用和诸如血管紧张素II等与压力无关的营养性刺激。为了分别研究这些影响，我们研究了在有或无血管紧张素II存在的情况下暴露于不同后负荷的离体工作心脏。
用改良的Krebs-Henseleit溶液灌注正常血压雌性Wistar大鼠的心脏，有或无血管紧张素II（100 nmol/L），并使其暴露于低（60 mmHg）或高（140 mmHg）后负荷（每组n>17）。通过Northern印迹分析评估左心室中原癌基因mRNA的诱导情况。
低后负荷时主动脉压力为101±14/63±6 mmHg（平均值±标准差），高后负荷时为175±13/93±20 mmHg；两组心脏在240分钟内均维持稳定的心输出量，但未灌注血管紧张素II的高后负荷心脏在实验结束时心输出量下降了59%（P<0.001）。与低（60 mmHg）后负荷相比，高（140 mmHg）后负荷时c-myc增加了50%（32%，72%）（几何平均值和95%置信区间），c-fos增加了54%（27%，86%），但H-ras受到抑制，降低了32%（25%，40%）（每项P<0.0001）。不同水平的高后负荷（110、120、140 mmHg）下c-myc和c-fos的诱导无显著差异，但H-ras的抑制随后负荷增加而逐渐增加（P=0.003）。在高后负荷时，c-fos水平在30分钟时升高，60分钟时达到峰值，c-myc持续升高至240分钟，H-ras在所有四个时间点均受到抑制。向灌注液中添加血管紧张素II（100 nmol/L）导致c-myc水平降低18%（6%，28%；P=0.006），c-fos水平降低12%（-6%，28%；P=0.18），H-ras升高11%（-0.1%，24%；P=0.056）。
离体灌注的工作大鼠心脏在与高血压中相当的高后负荷压力下能够稳定运行至少240分钟。仅通过压力增加即可诱导出与肥厚心脏中所见相似的原癌基因诱导，而无需循环血管紧张素II的介导作用。灌注血管紧张素II的心脏在高后负荷水平下表现出更稳定的性能，这与压力诱导的原癌基因表达变化的轻微减弱有关。
