Regulation of cartilage acid hydrolases by growth hormone

The in vivo regulation of three acid hydrolases, namely cathepsin D, cathepsin B, and acid phosphatase, by GH was investigated. The costal cartilage cathepsin D and acid phosphatase activities of hypophysectomized rats were reduced relative to those found in normal controls. Treatment of hypophysectomized animals with GH enhanced rat growth rate and increased these two enzyme activities toward normal levels. Results of pepstatin experiments suggested that the elevated cartilage cathepsin D activity corresponded to an increase in enzyme concentration. A degree of specificity in this regulation was apparent because cartilage cathepsin B, unlike cathepsin D and acid phosphatase, was refractory to hypophysectomy and GH treatment. In contradistinction to cartilage, none of these hepatic enzymes responded to GH, and only cathepsin B activity was diminished by hypophysectomy. Centrifugational and detergent studies indicated that changes in enzyme activities induced by GH treatment were not due to the differential release of acid hydrolases from subcellular compartments. Overall, our results suggest that costal cartilage cathepsin D and acid phosphatase activities are GH dependent and may be related to cartilage growth. These observations may provide insight into the mechanism of GH action and, derivatively, skeletal growth.