Abstract
Previous studies have demonstrated that collagen substrates stimulate in vitro somite chondrogenesis, and that agents that elevate intracellular cyclic AMP levels inhibit the ability of somites to respond to the inductive influence of collagen. In the present investigation, radioimmunoassay was utilized to compare the cyclic AMP content of somite explants cultured on purified Type I collagen substrates with control explants cultured on Millipore filters. During the period of culture, the cyclic AMP content of collagen‐treated explants is significantly lower than the cyclic AMP content of control explants. The cyclic AMP content of collagen‐treated explants is 66% of control values as early as one hour following the initiation of culture, and the cyclic AMP content of collagen‐treated explants remains lower than controls throughout the 3day culture period. The greatest difference in the cyclic AMP content of collagen‐treated and control explants is observed at the seventeenth hour of culture, at which time the cyclic AMP content of collagen‐treated explants is 56% of controls. These results combined with previous studies provide support for the hypothesis that collagen elicits a reduction in the cyclic AMP content of embryonic somites and that this reduction is necessary to trigger chondrogenic differentiation.