The growth of cultured rabbit articular chondrocytes is stimulated by pituitary growth factors but not by purified human growth hormone or ovine prolactin.

Recent reports describing a direct stimulation by GH of bone and cartilage growth led us to compare the in vitro mitogenic effects of highly purified human GH and PRL and two pituitary-derived growth factors in rabbit articular chondrocytes. These preparations were tested for their ability to promote [3H]thymidine incorporation into growth-arrested monolayer chondrocyte cultures and were also assayed in cell growth experiments. The factors tested included 22,000-dalton and 20,000-dalton human GH ovine PRL, glycosylated ovine PRL, bovine pituitary fibroblast growth factor (bpFGF), and a partially purified pituitary growth factor distinct from bpFGF. We found that no significant mitogenic effect was produced by either of the human GH or PRL preparations. Both of the pituitary-derived growth factors were potent mitogens, with bpFGF active at a final medium concentration of 10 pg/ml. These studies support the large body of evidence that GH has no significant direct in vitro effect on chondrocyte growth. The very potent effects of the pituitary-derived growth factors raise the possibility that their presence in GH preparations may be responsible for the in vitro mitogenic effects attributed to these preparations.

A leukemia virus-related protein in the murine pancreas.

A protein that has been detected in the granules of islet cells in the murine pancreas is similar but not identical to the endogenous murine leukemia virus envelope protein gp70. The pancreatic protein was detected by several immunological methods using both polyclonal and monoclonal anti-murine gp70. On purification by affinity chromatography, it was shown to be different from murine gp70 in its subcellular location and its molecular size and the size of its precursor and by the effect of various reagents on its immunological activity as determined by the ELISA assay.