Specific binding of growth hormone to isolated chondrocytes from rabbit ear and epiphyseal plate

Chondrocytes were isolated from rabbit ear, epiphyseal and rib cartilage, and their ability to bind 125I-labeled human growth hormone (hGH) was investigated. The total binding of hormone to ear chondrocytes increased with time until 4-6 h, whereas non-specific binding did not increase. Total binding was 1-3% of total counts added, and non-specific binding was 10-20% of total binding. Unlabeled hGH, bGH and oPRL competed with the binding of labeled hGH in a dose-dependent manner with half-maximal binding at concentrations of 10-20 ng/ml (hGH) and 100 ng/ml (bGH and oPRL). The two latter hormones displaced almost all specific binding of hGH at higher concentrations. Ear chondrocytes from newborn to 4 week old rabbits all showed specific binding of hGH with no clear age dependence. Rib chondrocytes, on the other hand, showed very little specific binding. Epiphyseal chondrocytes from newborn animals yielded intermediate binding values. The finding of specific hGH binding by cultured chondrocytes supports the concept of a direct effect of GH on chondrocytes.