Milkiewicz M, Brown M D, Egginton S, Hudlicka O
Department of Physiology, University of Birmingham, Birmingham, UK.
Microcirculation. 2001 Aug;8(4):229-41. doi: 10.1038/sj/mn/7800074.
To investigate the hypothesis that capillary proliferation in skeletal muscles, induced by a long-term increase in blood flow which elevates capillary shear stress, is associated with capillary expression of vascular endothelial growth factor (VEGF).
Adult rats received prazosin in drinking water ( approximately 2 mg per day) or had extensor digitorum longus (EDL) muscles stimulated by implanted electrodes for up to 14 days. At intervals, serial frozen sections of EDL were stained for alkaline phosphatase to identify capillaries, proliferating cell nuclear antigen (PCNA), and VEGF-A protein. Shear stress was estimated from capillary red blood cell velocities and diameters, measured by direct observation of epi-illuminated EDL.
Chronic stimulation and prazosin treatment both increased capillary: fiber ratio by approximately 40% after 14 days. In stimulated muscles, the percentage of capillaries positively stained for VEGF increased within 3 to 4 days, while the density of PCNA-positive capillaries had increased 20-fold after 2 days. With prazosin, VEGF-positive capillaries increased after 2 and 4 days, accompanied by a threefold increase in PCNA. By 14 days, PCNA labeling and VEGF were still high in stimulated muscles, but no longer different from controls with prazosin. After 3 to 4 days of treatment, capillary shear stress in resting muscle was 57% higher than in controls as a result of stimulation, but 4 times higher with prazosin.
Higher capillary shear stress with prazosin than with stimulation may upregulate VEGF expression in the early stages of treatment. Greater proliferation of capillaries preceding a higher proportion of VEGF-positive capillaries in stimulated muscles, in the presence of a modest increase in shear stress, suggests that angiogenesis was initiated by other factors in addition to shear stress.
探讨长期增加血流量从而提高毛细血管切应力所诱导的骨骼肌毛细血管增生与血管内皮生长因子（VEGF）在毛细血管中的表达相关这一假说。
成年大鼠饮用含哌唑嗪的水（约每天2毫克），或通过植入电极刺激趾长伸肌（EDL）长达14天。每隔一段时间，对EDL的连续冰冻切片进行碱性磷酸酶染色以识别毛细血管、增殖细胞核抗原（PCNA）和VEGF-A蛋白。通过直接观察落射照明的EDL来测量毛细血管红细胞速度和直径，从而估算切应力。
14天后，慢性刺激和哌唑嗪治疗均使毛细血管与肌纤维比例增加了约40%。在受刺激的肌肉中，VEGF阳性染色的毛细血管百分比在3至4天内增加，而PCNA阳性毛细血管密度在2天后增加了20倍。使用哌唑嗪时，VEGF阳性毛细血管在2天和4天后增加，同时PCNA增加了三倍。到14天时，受刺激肌肉中的PCNA标记和VEGF仍然很高，但与使用哌唑嗪的对照组不再有差异。治疗3至4天后，由于刺激，静息肌肉中的毛细血管切应力比对照组高57%，但使用哌唑嗪时则高4倍。
与刺激相比，哌唑嗪产生的更高毛细血管切应力可能在治疗早期上调VEGF表达。在切应力适度增加的情况下，受刺激肌肉中VEGF阳性毛细血管比例较高之前毛细血管的增殖更多，这表明除切应力外，血管生成还由其他因素启动。
