Effect of human growth hormone on proteoglycan synthesis in cultured rat chondrocytes

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Abstract
HGH [human growth hormone] stimulates DNA synthesis in cultured chondrocytes in the absence of serum. The effects of hGH on proteoglycan synthesis by cultured chondrocytes was studied. Chondrocytes were isolated from rat rib growth cartilage by collagenase digestion, plated in plastic dishes, transferred to serum-free MCDB 104 medium and incubated for 24 h to establish growth arrest. The cultures were then preincubated for 0-24 h with various concentrations of hGH and ovine prolactin (oPrl) and finally pulse-labeled for 30 min with radioactive sulfate in the presence of hormone, hGH, but not oPrl, stimulated sulfate incorporation with an apparent maximum at 50 ng/ml (.apprx. 170%). The stimulatory effect was apparent after 2 h and maximal after 3 h preincubation. After 12 h the stimulatory effect had decreased to insignificant levels. Qualitative analysis of isolated proteoglycan indicated that the stimulated of sulfate incorporation by hGh is exerted at the level of protein synthesis with little effect on glycosylation and sulfation. Further experiments are required to demonstrate whether the stimulatory effect on proteoglycan synthesis is a specific phenomenon or represents one aspect of a general stimulation on cell metabolism in preparation for DNA synthesis.