目的 探讨小鼠胚胎呼吸内胚层相关第二生心区（PSHF）发育与流出道远端形态发生的关系。 方法 用免疫蛋白印迹法检测抗胰岛因子-1(ISL-1)在80例胚龄10～14 d小鼠胚胎心脏标本的表达。另用抗ISL-1、抗α-平滑肌肌动蛋白(α-SMA)及抗心肌肌球蛋白重链(MHC)抗体，对36例胚龄11～13 d小鼠胚胎心连续石蜡切片进行免疫组织化学或免疫荧光染色。 结果 胚龄11～12 d是ISL-1蛋白在小鼠胚胎心脏表达的高峰时段。胚龄11 d，来自鳃弓或心包腔背侧壁等处PSHF的ISL-1阳性细胞延伸进入流出道远端管壁，流出道远端管壁则失去MHC表达，呈α-SMA阳性表达；来自PSHF的ISL-1阳性细胞则围绕呼吸内胚层呈对称性锥体结构分布，锥体顶端突入动脉囊腔呈ISL-1阳性突起。胚龄11.5 d，PSHF锥体顶端进入动脉囊头侧和尾侧管壁，形成流出道远端管壁上对称的ISL-1阳性柱结构；而动脉囊腔尚未分隔，流出道远端仍为单一管道。 胚龄12 d，PSHF锥体突起失去ISL-1表达，呈较强的α-SMA表达。在PSHF锥体突起与流出道嵴融合前，两者之间出现主-肺动脉孔；两者融合后则形成α-SMA阳性的暂时性主-肺动脉隔，将动脉囊分隔成MHC阴性的心包内的主动脉和肺动脉。胚龄13 d，主-肺动脉隔逐渐消失，心包内主动脉和肺动脉分离。在MHC阴性的心包内大动脉管壁上出现了α-SMA阳性的平滑肌层，仍可见少量PSHF的ISL-1阳性细胞延伸进入心包内大动脉管壁。 结论 在小鼠胚胎发育11～13 d，PSHF将动脉囊分隔成心包内的主动脉和肺动脉，并参与心包内大动脉的侧面管壁和对侧面管壁的分化形成。

Objective To explore the relationship between the development of pulmonary endoderm-associated second heart field (PSHF) and the morphogenesis of the distal outflow tract in mouse embryonic heart. Methods The islet-1 (ISL-1) expression in 80 mouse embryonic hearts from embryonic days (ED) 10 to ED 14 was detected by Western blotting. Both the immunohistochemistry and immunofluorescence staining method were used to observe ISL-1, α-smooth muscle actin (α-SMA）and myosin heavy chain (MHC) distribution in serial sections of 36 mouse embryos from ED 11 to ED 13. Results The peak period of ISL-1 protein expression in mouse embryonic heart was from ED 11 to ED 12. At ED 11, the ISL-1 positive cells from branchial arch or dorsal wall of pericardium, belonging to PSHF, extended into the distal outflow tract, which lost MHC expression and showed α-SMA positive. The ISL-1 positive cells from PSHF formed thecone-shaped structure centered by pulmonary endoderm, which protruded into aortic sac and produced the ISL-1 positive protrusion in aortic sac. At ED 11.5, though aortic sac was still not separated, the extension of PSHF to the cranial and caudal myocardial wall of aortic sac was detected as two ISL-1 positive symmetrical boluses in outflow tract wall. Instead of MHC, the protrusion of PSHF became α-SMA expression at ED 12. Before the fusion of PSHF protrusion and outflow tract cushions, a small channel called the aortic-pulmonary foramen was observed. By later ED 12, PSHF protrusion completed fusion with outflow tract cushions generated the α-SMA positive and transient aortic-pulmonary septum, which divided aortic sac into the intrapericardial aorta and pulmonary trunks which were MHC negative. At ED 13, the aortic-pulmonary septum gradually disappeared, and the intraper-ardial aorta and pulmonary trunks separated finally, which were MHC negative and in which α-SMA positive smooth muscle layers were observed. The extension of a few ISL-1 positive cells from PSHF toward the intrapericardial aorta and pulmonary trunks walls was continuing. Conclusion From ED 11 to ED 13 in normal mouse embryos, PSHF divides aortic sac into the intrapericardial aorta and pulmonary trunks, and is responsible for the lateral and facing walls of intrapericardial trunks.