Stimulation of sulfate and thymidine incorporation into hypophysectomized rat cartilage by growth hormone and insulin-like growth factor-I in vitro: the somatomedin hypothesis revisited.

These studies were undertaken in an attempt to demonstrate sensitivity of cartilage from hypophysectomized rats to growth hormone (GH) in physiologic concentrations in vitro and to compare the actions of the hormone and extrinsic insulin-like growth factor-I (IGF-I). In a HEPES-buffered, amino acid-glucose nutrient medium with a low concentration of bovine serum albumin, costal cartilage explants from such animals were responsive to purified or recombinant bovine GH (bGH) and recombinant human GH (hGH) with a sensitivity of less than 100 ng/ml [corrected]. Sulfate incorporation into proteoglycans and thymidine incorporation into DNA were increased.

Similarity of somatomedin inhibitor in sera from starved, hypophysectomized, and diabetic rats: distinction from a heat-stable inhibitor of rat cartilage metabolism.

The inhibitory effects of sera from starved, hypophysectomized, and alloxan-diabetic rats on basal and somatomedin-stimulated sulfate incorporation into cartilage from hypophysectomized rats were compared. The somatomedin inhibitory activity in serum from diabetic rats behaved like that in serum from starved rats on heating at 60 C. Both were labile in the native sera (pH 8.