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1 GROWTH HORMONE (GH) DIRECTLY ENHANCES CHONDROGENESIS AND OSTEOGENESIS IN VITRO

To study the direct effect of GH on chondrogenesis and osteogenesis 2 model systems were used. An organ culture of newborn mice mandibular condyle were maintained on collagenous sponge, cemented onto stainless steel mesh for 6 days. The addition of 50 ng/ml recombinant human GH (hGH) caused within 3 days a marked enlargement of the proliferative zone from 56±6 to 120±11 microns. The width of the chondroblast layer increased by hGH from 66±9 to 199±7 microns, reflecting significant proliferation, and that of the chondrocytic layer from 288±22 to 465±9 microns, reflecting differentiation. The calcified cartilage shrank from 400±12 to 333±29 microns. In a separate tissue culture system of mice chondroprogenitor cells, the undifferentiated cells developed within 3 days to a cartilage nodule which by 6 days grew further. The addition of 50 ng/ml hGH to the medium produced a marked increase in the nodule size from 20±2 to 46±6 and from 76±7 to 380±12 mm2 on days 3 and 6 resp. The perichondrium width increased from 100±12 to 149±7 microns on day 6, and that of the cartilage layer from 242±10 to 477±12 microns. Moreover, under hGH we observed the appearance of calcified cartilage and osteogenesis of bone trabecules, osteocytes, osteoblasts and osteoclasts, which were absent in the absence of hGH. We conclude that hGH has a direct effect on chondrogenesis and osteogenesis in tissue and organ culture, which are both proliferative and differentiative.