Vascular localization and proliferation in the growing tip of the deer antler.

The process of angiogenesis is of interest because of the significant clinical benefits associated with controlling vascular growth. Within the antler, chondrogenesis and antler elongation are occurring at the rate of 1-2 cm per day and thus blood vessels are growing at this same rapid pace. We demonstrate that the process of angiogenesis in the antler is controlled at various tissue locations. The findings clearly differentiate the spatial location of the stem cells that drive chondrogenesis from the proliferation process driving the angiogenesis. Vessels within the lateral dermis contained BrdU-positive cells, suggesting that these vessels were elongating. Within the precartilage region, proliferating vessels were detected in bundles of complex structure evenly distributed throughout this tissue layer. The support cells within these bundles of vessels were detected by staining with alpha-smooth muscle actin, while the endothelial cells were negative. Additionally, the alpha-smooth muscle actin staining was found in association with the cartilage cells of the antler. The marked proliferation of the vascular associated cells in the precartilage region identified this area as a major region of vascular growth in the antler. We propose that within the precartilage region, the most likely mechanisms to explain the observed vascular morphology are that of vascular extension of the existing vessels and intussusceptive angiogenesis or sprouting to generate the small bundles of vessels. Wiley-Liss, Inc. (c) 2006 Wiley-Liss, Inc.