| Angiogenesis, the process of sprouting new capillaries from pre-existing vessels, is the most fundamental and important course in vivo and a crucial way to keep the stability and integrity of the body and maintain the functions of tissues and organs. Vascular endothelial growth factor (VEGF) is a mitogen specific for endothelial cells and plays a modulatory role almost at each stage of angiogenesis. VEGF rarely expressed in normal heart, but the expression of VEGF increases after ischemia or hypoxia. It has been proved that the expressions of all VEGF isoforms vary greatly in distinct organs during different stages. The most primary isoforms expressed in the heart are VEGF121, VEGF165 and VEGF189 (one amino acid fewer in rats than in human beings). The expressions of VEGF isoforms are different at different stages and at the different time point after myocardial ischemia in myocardial and endothelial cells. The expressions in the peripheral and myocardial vascular endothelial cells are different as well. VEGF promotes angiogenesis through its receptors VEGFR-1 and VEGFR-2. Miraliakbari R et al found that VEGFR-2 mRNA increased at acute ischemia, but the expression ofVEGFR-2 had different characteristics in peripheral and in myocardial endothelial cells. At present, the research of the growth factor related to angiogenesis focused mostly on the peripheral vessels and young animals are mostly used as experimental objects in the researches. Previous study has indicated that the impaired angiogenesis accompanied with body senescence is associated with the decreasing expression of VEGF. The proliferative ability of endothelial cells in blood vessels from the aged tends to decrease and the addition of VEGF can contribute to the recovery of the ability. However, there are few reports about the characteristics of VEGF isoforms expressed in the heart of the aged, about the impact of senescence on the expression of VEGFR in the heart and about the mechanism of the impaired angiogenesis accompanied by aging.In this study, we studied the change of the expression of VEGF mRNA isoforms, VEGFR-1 and VEGFR-2 mRNA at ischemia myocardium border in the heart of aged rats at lh, 3h, 6h, Id, 3d and 7d after myocardial ischemia by taking GAPDH as the inner control gene, expanding both the aimed gene and the inner control gene in the same tube by reverse-transcription and semi-quantity polymerase chain reaction (RT-PCR).Our results showed that: (1) In ligating the left anterior descending (LAD), the great cardiac vein should not be used as the sole reference point, and the left atria and the pulmonary arteria taper should also be used as reference points. Application of improved "U type" needle could solve the problem of the narrow chest and eliminate the bad effect brought about by the beating heart on the blood vessel in the ligation of LAD, thus reducing the mortality rate of early death. (2) The level of the expression of total VEGF and its isoforms in myocardium was quite low in the young and aged rats inboth normal control and sham-operation groups. (3) The expression of VEGF mRNA increased in both young and aged rat heart during myocardial ischemia. Compared with that of the young rats, the total VEGF mRNA of the aged in the heart was significantly lower in every stage of ischemia (p<0.01) and the VEGF peak value was delayed in aged rat heart after ischemia. (4) At every predetermined time point, the expression of VEGF 164 had the highest proportion in total VEGF in both aged and young rats after myocardial ischemia, while VEGF 120 had the lowest proportion. The proportion of VEGF188 was higher in aged rats than that in young rats. (5) Our RT-PCR experiments displayed that VEGFR-1 mRNA was higher in young rats than that in aged rats (0.26+0.23X10-2 vs 0.20 + 0.59X10-2, p<0.01) . After myocardial ischemia, the expression of VEGFR-1 mRNA increased in both young and aged rats. The expression reached the peak 1 hour after ischemia and then it began to descend. After ischemia, the expression of VEGFR-1 mRNA in the aged was lower than that in the young rats at different time point. (6) The expression of VEGFR-2 mRNA in the heart was also obviously different between the young rats and the aged rats after ischemia. The expression of VEGFR-2 mRNA in young rats reached its peak value 1 hour after ischemia and decreased quickly, but there was no notable alteration in the aged rats.From the above results we conclude that: (1) The lower expression of VEGF in the aged rats indicates that the reaction of myocardium of the aged rats to hypoxia is blunt, which may come from the low secretion of VEGF in aged rats. (2) In the aged rats, the increased the propotion of VEGF 188, which as no ability of angiogenesis, and decreased proportion of VEGF 120 and VEGF 164, which are the main factors in angiogenesis, may be responsible for...
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