Effects of dibutyryl cyclic AMP and theophylline on in-vitro development of the secondary palate in the embryonic chick.

The avian secondary palate is normally cleft and does not show a rise in intracellular cyclic AMP like that of the fused mammalian palate. The secondary palate of the embryonic chick (HH stages 25-34) was exposed in vitro to dibutyryl cyclic AMP and theophylline to determine whether raising intracellular cyclic-AMP levels would alter medial-epithelial development. Differentiation of the medial epithelium was not altered but there was mucous-cell hyperplasia in nasal epithelium and inhibition of membrane-bone formation in the mesenchyme. Thus the developmental factors that cause the avian palate to be cleft and the mammalian palate to be fused are more complex than differences in intracellular cyclic-AMP levels.