ABSTRACT
In this experiment, pregnant Sprague-Dawley rats were treated with 100mg/kg of alltrans retinoic acid at 10th day of gestation. Pregnant rats were sacrificed at gestation day 14, 15, 16 and 18. Fetuses were delivered, and palatal processes were dissected. The specimens were prepared with fibronectin immunohistochemical stain, and mesenchymal changes were observed with electron microscope. The results were as follows. 1. In the findings fo fibronectin immunohistochemial stain, a part of the mesenchyme of the palatine process of the control group showed weak positive reaction at 14th gestation day, and the reactivity increased progressively by each day. In retinoic acid treated group, the positive reaction was trace at 14th day of gestation, and the reactivity increased progressively, but it was weaker than that of the control group. 2. Examination under transmission electron microscopy revealed well-developed rough endoplasmic reticulum, Goigi apparatus, mitochondrias which were found at the palatine process of the control group. In the retinoic acid treated group, at 16th and 18th day of gestation, the mesenchymal cells of the elevated palatine process had fragmented, sacculated rough endoplasmic reticulums, their mitochondrias were swollen and dissolved, In all cases with retinoic acid treated group, mitotic cells at various stages were more frequently found than in control group. In conclusion, the retinoic acid induces alterations of the intracytoplasmic organells. This finding suggests that retinoic acid is ditectly cytotoxic to mesenchymal cells. Positive fibronectin reaction was demonstrated before palatal elevation at th 15th day of gestation. Therefore, it could be postulated that mesenchymal cells synthesize and release the fibronectin. In the retinoic acid treated group, fibronectin showed positive reaction before and after palatal elevation, and it suggests that fibronectin would be involved in palatal elevation.