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Microvascular pattern in the metaphysis during bone growth
S Aharinejad1, S C Marks, P Böck
1First Department of Anatomy, University of Vienna, Austria.
Background:
Little is known about the three-dimensional micromorphology of vessels in the growth zone of long bones, where significant vasculogenesis occurs. Therefore, we examined the microvascular pattern of the femoral metaphysis.
Methods:
Six-week-old normal rats of either sex were used. We cast the femurs of 14 rats with Mercox for scanning electron microscopy (SEM), and in 10 rats we prepared tissue sections of femurs for light (LM) and transmission electron microscopy (TEM).
Results:
In the LM, calcified cartilage was found to define cylindrical compartments beneath the last row of hypertrophied chondrocytes of the metaphyseal growth plate. These compartments ran in the bone's longitudinal axis and contained a single capillary profile. Endothelial cells of these capillaries often showed increased cytoplasmic volume and loose texture of nuclear chromatin. Cast metaphyses by SEM showed numerous parallel vascular loops with nodular protrusions 10-12 microns in diameter at their tips. The loops had ascending and descending limbs with a luminal diameter of 10-14 microns. Small projections 4-5 microns in diameter and delicate crests were sometimes found on the tip of the larger nodes. In a 100 x 100 microns area, there were 14-17 large nodes. By TEM, capillary sprouts were identified at the level beneath the last row of hypertrophied chondrocytes. These capillaries had voluminous endothelial cells rich in free ribosomes and rough endoplasmic reticulum. Endothelial cell nuclei were rounded and showed loose chromatin texture. Endothelial cells were connected by intermediate junctions and there was no basal lamina. Deeper into the metaphysis, arterioles and sinusoids were present.
Conclusions:
We conclude that the metaphyseal plate of the growing rat offers an optimal model to study vasculogenesis. Capillary sprouts can be readily identified, measured, and counted because they are located within a plane bordering against avascular cartilage. In addition, by using microvascular corrosion casting in SEM not only capillary sprouting per se but also different stages of neovascularization, indicated by differently sized nodular projections at the tip of vascular loops, can be studied in the growing long bone.
Insights
This study reveals the intricate vascular network in rat long bone growth zones. Microvascular corrosion casting and microscopy identified capillary sprouts and neovascularization stages, offering a model for studying blood vessel formation.
Area of Science:
- Vascular Biology
- Skeletal Development
- Microscopy
Background:
- The three-dimensional micromorphology of vessels in long bone growth zones is poorly understood.
- Vasculogenesis, the formation of new blood vessels, is a significant process in these areas.
Purpose of the Study:
- To examine the microvascular pattern of the femoral metaphysis in rats.
- To investigate the three-dimensional micromorphology of vessels during vasculogenesis in long bones.
Main Methods:
- Utilized scanning electron microscopy (SEM) with microvascular corrosion casting on rat femurs.
- Employed light microscopy (LM) and transmission electron microscopy (TEM) on tissue sections.
Main Results:
- Identified capillary sprouts with unique endothelial cell characteristics beneath the growth plate.
- SEM revealed parallel vascular loops with nodular protrusions, indicating different neovascularization stages.
- Quantified vascular structures, noting 14-17 large nodes per 100x100 microns area.
Conclusions:
- The metaphyseal plate of growing rats is an optimal model for studying vasculogenesis.
- Capillary sprouts are identifiable and measurable in this model.
- Microvascular corrosion casting combined with SEM allows detailed study of neovascularization stages.