IMMUNOHISTOCHEMICAL ANALYSIS OF EGF IN EPIPHYSEAL GROWTH-PLATE FROM NORMAL, HYPOPHYSECTOMIZED, AND GROWTH HORMONE-TREATED HYPOPHYSECTOMIZEDRATS

Epiphyseal growth plate cartilages from the proximal tibia of normal, hypophysectomized, and growth hormone (GH)-treated hypophysectomized r ats were subjected to immunohistochemistry for detection of epidermal growth factor (EGF). In the normal growth plate, EGF was distributed m ainly in the proliferative zone. Hypophysectomy resulted in considerab le atrophy of the chondrocytes and the cartilage matrix (a decreased n umber of mature-type chondrocytes and a decreased ratio of proliferati ng to hypertrophic chondrocytes) and a significant diminution of EGF i mmunoreactivity. Treatment with GH reversed these effects of hypophyse ctomy, causing an increased thickness of the growth plate and EGF-reac tive sites in all chondrocyte layers. The most intense immunostaining for EGF, however, was frequently seen in the nuclei of chondrocytes wi th flattened appearance. It appears that EGF could be incorporated or synthesized in chondrocytes having marked mitogenic activity. The pres ent results, taken with previous data on EGF involvement in growth of cartilaginous tissue in vivo and in vitro, strongly suggest that EGF-i mmunoreactive chondrocytes are involved in cartilage proliferation and growth under the specific influence of GH.