Abstract
We investigated the relationship between morphological changes due to angiogenesis and expression of type II and type X collagen mRNA in rat growth plate. Histological examination revealed that the growth plate became thinner over time and that capillaries had penetrated the hypertrophic zone at 16 weeks of age. Immunohistochemistry showed that both the type II collagen-positive cells predominantly localized in the proliferative zone, and the type X collagen-positive cells, predominantly localized in the hypertrophic zone, diminished in number as the number of weeks of age increased. Further investigation by the reverse transcription-polymerase chain reaction (RT-PCR) showed that the level of expression of type X collagen mRNA was highest at 4 and 8 weeks, and considerably lower at 16 and 36 weeks, while the highest level of type II collagen mRNA expression was at 4 weeks, gradually decreasing thereafter. Our findings demonstrated that angiogenesis itself caused changes in the extracellular environment around the hypertrophic chondrocytes, and that this became a factor causing the decrease in production of type X collagen.
