Differential effects of parathyroid hormone on chick growth plate and articular chondrocytes

Parathyroid hormone (PTH) binds specifically to the hypertrophic region of growth plate cartilage [16]. This specific binding suggests a role for this hormone in chondrocyte maturation. Enzymatically isolated chick articular and growth plate chondrocytes grown in monolayer culture were used to assay the direct effects of PTH on chondrocytes. The articular chondrocytes were unresponsive to PTH. The growth plate chondrocytes, however, demonstrated a marked mitogenic response to PTH, with a 39-fold increase of [³H]-thymidine incorporation into DNA. PTH also affected matrix production by the growth plate chondrocytes causing a twofold stimulation of proteoglycan synthesis as determined by the rate of ³⁵SO₄ incorporated into matrix macromolecules. Furthermore, PTH depressed collagen synthesis as measured by [³H]-proline incorporation. PTH caused a 12-fold increase in intracellular cAMP in growth plate chondrocytes but no increase in the articular cells. This specificity of PTH for growth plate chondrocytes suggests a possible regulatory role in enchondral ossification.