A factor produced by cultured rat leydig tumor (rice-500) cells associated with humoral hypercalcemia stimulates adenosine 3′, 5′-monophosphate production via the parathyroid hormone receptor in human skin fibroblasts

The Rice-500 Leydig cell tumor of Fischer rats is associated with humoral hypercalcemia invivo and produces a factor that stimulates ^cAMP formation in cultured rat osteosarcoma cells. We found that cultured human skin fibroblasts respond to both human PTH-(1 34) and the factor produced by cultured rat Leydig tumor cells with a dose-dependent rise in ^cAMP formation. The time courses for stimulation of the two agents were similar, and stimulation by both was blocked by the competitive PTH antagonist [8, 18-norleucine, 34-tyrosine]bovine PTH-(3 34) amide. These data suggest that PTH-like factors secreted by a murine tumor are capable of interacting with the human PTH receptor.