Somite chondrogenesis: alterations in cyclic AMP levels and proteoglycan synthesis.

Cyclic AMP (cAMP) levels have been shown to have a positive influence on chondrogenesis in limb buds and pelvic cartilage. In the present study the level of cAMP was measured during somite chondrogenesis in vitro and found to decrease from 1.38 pmol/micrograms DNA on day 0 to 0.9 pmol/micrograms DNA on day 6. Inclusion of notochord with somites caused a marked reduction, with levels decreasing from 1.41 pmol/micrograms DNA on day 0 to 0.36 pmol/micrograms DNA on day 6. Concurrently, the incorporation of radioactive sulfate into sulfated glycosaminoglycans increased from day 3 to day 6 by 38% in somite and 77% in somite-notochord explants. The aggregation of proteoglycans was analyzed by gel chromatography and found to increase with a corresponding decrease in cAMP levels. The results indicate that a decrease in cAMP levels may be necessary for chondrogenic expression in somites.