[Electron microscope studies of the structure and junctions of heart and skeletal muscle capillaries in the rat during pre- and postnatal development]. / Elektronenmikroskopische Untersuchungen zur Struktur der Junctionen von Herz- und Skeletmuskelcapillaren der Ratte während der prae- und postnatalen Entwicklung.

Comparative investigations with freeze etching procedure of capillaries of the rat heart and triceps muscle (fetal and some postnatal stages) reveal some differences of the junctional structures. Junctions of the skeletal muscle capillaries show several parallel arranged rows of partly linked and interrupted junctional strands with relative few junctional particles. In the 3rd week of life, we found also short fragments of non parallelized strands densely covered with particles which could be related to the venous segment of the capillary. The junctions of myocardial capillaries show a reduced number of mostly zigzag-like arranged junctional strands with many particles and large non sealed gaps. Areas with extremely reduced strands were kept for the venous segments. The above described differences could be responsible for the better permeability of the heart capillaries to horse radish peroxidase.

[Electron microscopic study of the permeability of terminal blood vessels of the M. triceps brachii to horseradish peroxidase in fetal, juvenile and adult rats]. / Elektronenmikroskopische Untersuchungen zur Permeabilität von Blutgefässen der terminalen Strombahn des M. triceps brachii fetaler, jugendlicher und erwachsener Wistar-Ratten für Meerrettichperoxidase.

At the basis of some ultrastructural differences in fetal, juvenile and adult rat triceps muscle capillaries as described in preliminary papers the permeability of these capillaries to horse radish peroxidase was investigated. Capillaries of fetal and juvenile rats up to the 3rd week after birth were impermeable to horse radish peroxidase (HRP) for 2 and 10 minutes after injection, which can be explained with the low pinocytotic activity and the more complex structure of the junctions. Capillaries of the triceps brachii muscle in adult rats aged 2 month and more show a low permeability to HRP 2 and 5 minutes and a high permeability 15 minutes after the injection of the tracer. In the capillary segment of the terminal bed the tracer was traversed especially by the means of vesicles and some transendothelial channels built by linked vesicles. The interendothelial junctions seemed to be tight. In the venular segment of th capillaries and in small postcapillary venules additional to the vesicular transport a high permeability of some junctions was stated. The significance of the different permeability of distinct segments of the terminal vascular bed to small macromolecules is discussed with respect to the theories of th physiologists and compared with the results of recent investigators.