求翻译：ATRA是维生素Ａ的天然衍生物，在细胞系的建立、细胞分化和增殖中发挥重要作用。国内外对ATRA对血管平滑肌的抑制作用做了大量的研究，ATRA是很有希望的防治RS的药物[7。8]，而对血管内皮作用的研究少有报道。Carlo等[1]报道ATRA对体外培养的猪主动脉内皮细胞有增生作用，在50 nmol/L时对血管内皮细胞的增生作用达到峰值，细胞数增加107±10%（P＜0.05），能够刺激血管的形成。本实验结果与上述结果有所差异，考虑与分组不够细有关。ATRA促进内皮细胞增生的机制，Carlo等认为可能为维甲酸在合适的条件下通过增加内皮细胞RAR-α依赖的FGF-2（成纤维细胞生长因子）在mRNA和蛋白水平的表达，同时上调尿激酶型血纤溶酶原激活物（U-PA），对血管内皮细胞有增生作用并且促进血管的形成，而在较高浓度下对血管内皮细胞未表现出增生作用，其机制尚不清楚。是什么意思？

ATRA is a natural vitamin a derivatives, in the establishment of cell lines, cell differentiation and proliferation play an important role. At home and abroad on the inhibitory effect of ATRA on vascular smooth muscle has done a lot of research, ATRA is a very promising drugs for prevention and treatment of RS [7. 8], the study of vascular endothelial function and rarely reported. Carlo [1] reports of ATRA on cultured porcine aortic endothelial cell proliferation, in 50 nmol/L on vascular endothelial cell proliferation of peak, ± 10% increase in cell number 107 (P<0.05), can stimulate blood vessel formation. Results of this experiment and the above result is different, consider grouping is not fine enough-related. ATRA promote endothelial cell hyperplasia of mechanism, Carlo, think may for dimension formic acid in suitable of conditions Xia through increased endothelial cell RAR-α rely on of FGF-2 (into fiber cell growth factor) in mRNA and protein level of expression, while raised urine kinase type blood fiber dissolved enzyme original activation property (U-PA), on vascular endothelial cell has hyperplasia role and promote vascular of formation, and in higher concentration Xia on vascular endothelial cell not performance out hyperplasia role, its mechanism is not clearly.