Development of the collagen network of the human fetal myocardium: an immunohistochemical study

We have studied the development of the collagen network within the ventricular myocardium of sixteen human fetuses of gestational age 12 weeks to 22 weeks. Using the technique of indirect immunohistochemistry with antibodies raised against collagen Types I and III, we have demonstrated that the 12 week old heart has a rudimentary endomysial collagen structure which coexpresses both collagen types. Perimysial structures evolve with the onset of the second trimester and are collagen III positive before expressing collagen Type I. No differences in collagen deposition were detected between the right and left ventricular free walls, but collagen content of the interventricular septum appeared relatively high and expressed in thick highly organised fibrils. Transventricular gradients of collagen distribution were seen for both collagen isoforms which persisted with increased age. Intraventricular differences in collagen deposition were marked due to the insertion of the atrioventricular valves and tension apparatus. These findings suggest that the collagen network of the fetal myocardium is composed of copolymer fibrils, possibly rich in collagen type III which evolve at a time when the mechanical efficiency of the fetal heart must improve to keep pace with the escalating demands of a rapidly growing body.