Changes in cyclic AMP and cyclic GMP levels during in vitro chondrogenesis.

cAMP and cGMP levels were measured in micro high-density cultures of chick limb bud mesenchyme cells stages 22-24 after 1, 2, 4 and 6 days of culturing. In these cultures, a consistent cartilage differentiation proceeds parallel to the progressive accumulation of cells in the G0 phase. The cAMP level increased by 45% by the time of the onset of cartilage phenotype expression, and significantly decreased thereafter. The cGMP level gradually diminished by a total of 39% during the period examined. It is suggested that the decrease in cell proliferation may be the consequence of the reduction of the cGMP level, and that a short-term marked elevation of cAMP level induces cartilage differentiation in the limb mesenchymal cells which are able to select only from a limited number of differentiation programmes.