Morphological variety of capillary ends invading the epiphyseal plate in rat femora using scanning electron microscopy with osmium maceration.

The function of capillary ends at the epiphyseal plate has been actively investigated. However, their morphology is still poorly understood. This study was designed to examine the capillary ends invading the epiphyseal plate three-dimensionally by scanning electron microscopy and discuss the relationship between their morphology and function. Distal halves of the femora of eight-week-old male Wistar rats were used. The specimens were divided into two groups for transmission and scanning electron microscopy. For transmission electron microscopy, sagittal ultrathin sections were routinely prepared after the demineralization of the specimens, and the chondro-osseous junction was examined at the epiphyseal plate. For scanning electron microscopy, the specimens were sagittally freeze-cracked, osmium-macerated, and routinely processed. Endothelial cells of capillary ends had fine fenestrations, and hence they were distinguishable from perivascular cells (also known as septoclasts). Based on the outline and the presence or absence of pores, the capillary ends were divided into four types: closed dome, closed spire, porous dome, and porous spire. The two dome types generally occupied more than half of a lacuna, whereas the two spire types generally occupied only a small part of a lacuna. The porous types engulfed cellular remnants, indicative of degraded chondrocytes, via their pores. Some of the spire types penetrated the transverse septum. The morphological variety of capillary ends reflected their functional variety. Observations suggest that the capillary ends change their morphology dynamically in response to various functions, including the removal of degraded chondrocytes and perforation of transverse septa.

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