Lamparter S, Sun Y, Weber K T
Department of Internal Medicine, University of Missouri Health Sciences Center, Columbia, USA.
Cardiovasc Res. 1999 Jul;43(1):165-72. doi: 10.1016/s0008-6363(99)00111-x.
Fetal cardiac development includes rapid formation of a three-dimensional collagen network, composed mainly of type I and III fibrillar collagens. Collagen fibrils have been found in cardiac jelly at very early stages of cardiac development and are thought to have structural and functional properties. In adult rat cardiac tissue, angiotensin II (AngII) via AT1 receptor binding and AngII-regulated expression of transforming growth factor beta-1 (TGF-beta 1) each upregulate collagen transcription. AT1 and AT2 receptor subtypes are developmentally regulated; both have been localized in fetal tissue where the AT2 receptor is considered a determinant of morphogenesis. We sought to determine whether blockade of either receptor would result in attenuation of collagen mRNA expression and fibrillar collagen accumulation and alter TGF-beta 1 mRNA expression in the developing fetal heart examined at birth.
Pregnant rats were treated either with an AT1 receptor antagonist losartan or an AT2 receptor antagonist PD123319 and compared with untreated age-matched controls. Offspring were studied within 24 h of birth. Type I and type III collagen mRNA expression, as well as TGF-beta 1 mRNA expression, were examined by in situ hybridization. Collagen concentration was determined spectrophotometrically by picrosirius red staining and type I and III collagens were detected by immunoblotting.
We found: (1) comparable birth weights in control and PD123319-treated animals, but reduced body weight in newborn losartan-treated animals; (2) compared to untreated animals, type I collagen and TGF-beta 1 mRNA expression in cardiac tissue were each equally reduced in both losartan and PD123319-treated animals; (3) increased type III collagen mRNA expression in both PD123319- and losartan-treated groups; and (4) a significant decrease in total soluble cardiac collagen concentration in both losartan and PD123319-treated groups, confirmed by attenuated immunoreactivity of type I and III collagens in whole heart extracts by Western blotting.
The results of these pharmacologic interventions suggest AngII receptors are expressed in cardiac tissue during gestation, where both AT1 and AT2 receptors are involved in the regulation of type I and III collagen expression and structural protein accumulation. These effects appear to be mediated, in part, by attenuated cardiac TGF-beta 1 levels. The marked decrease in newborn cardiac collagen content has yet undefined functional consequences.
胎儿心脏发育包括一个主要由I型和III型原纤维胶原蛋白组成的三维胶原蛋白网络的快速形成。在心脏发育的早期阶段，已在心脏胶冻中发现胶原蛋白原纤维，并且认为其具有结构和功能特性。在成年大鼠心脏组织中，血管紧张素II（AngII）通过AT1受体结合以及AngII调节的转化生长因子β-1（TGF-β1）表达上调，各自上调胶原蛋白转录。AT1和AT2受体亚型在发育过程中受到调节；两者均已定位在胎儿组织中，其中AT2受体被认为是形态发生的决定因素。我们试图确定在出生时检查的发育中的胎儿心脏中，阻断任一受体是否会导致胶原蛋白mRNA表达和原纤维胶原蛋白积累的减弱，并改变TGF-β1 mRNA表达。
将怀孕大鼠用AT1受体拮抗剂氯沙坦或AT2受体拮抗剂PD123319进行处理，并与未处理的年龄匹配的对照组进行比较。在出生后24小时内对后代进行研究。通过原位杂交检查I型和III型胶原蛋白mRNA表达以及TGF-β1 mRNA表达。通过天狼星红染色分光光度法测定胶原蛋白浓度，并通过免疫印迹法检测I型和III型胶原蛋白。
我们发现：（1）对照组和用PD123319处理的动物出生体重相当，但用氯沙坦处理的新生动物体重降低；（2）与未处理的动物相比，氯沙坦和PD123319处理的动物心脏组织中I型胶原蛋白和TGF-β1 mRNA表达均同等程度降低；（3）PD123319和氯沙坦处理组中III型胶原蛋白mRNA表达均增加；（4）氯沙坦和PD123319处理组中总可溶性心脏胶原蛋白浓度均显著降低，通过蛋白质印迹法检测全心脏提取物中I型和III型胶原蛋白免疫反应性减弱得以证实。
这些药物干预的结果表明，AngII受体在妊娠期间在心脏组织中表达，其中AT1和AT2受体均参与I型和III型胶原蛋白表达以及结构蛋白积累的调节。这些作用似乎部分是由心脏TGF-β1水平减弱介导的。新生心脏胶原蛋白含量的显著降低尚未明确其功能后果。
