Abstract
In order to elucidate the pathogenesis of cleft lip, a single intraperitoneal injection of 0.2mg/kg vincristine was performed in rats on 8th day and 12 hours of gestation and embryos were extracted during the period from 10th day and 18 hours to 14th day and 12 hours of gestations at 6-hour intervals for observation by scanning electron and light microscopy, the result of which described as follows.
1. Cleft lip were observed in 69.5% of the embryos during the period from 14th day and 0 hour to 14th day and 12 hours (median cleft lip 25.4%, lateral cleft lip 44.1%).
2. Variable hypoplasias of facial processes were observed, and two types of hypoplasias were recognized in them. One was the extreme hypoplasia or aplasia of the frontal processes, the other was the h ypoplasia of the medial and the lateral nasal procsses, especially the lateral nasal processes.
3. Differentiation of the surface epithelium on facial processes was delayed, and the number and the density of the mesenchymal cells were low.
4. The incidence of spheroidal particles, filopodial projections and cellular processes on the surface epithelium and the incidence of the pycnosis figures in epithelial cells and mesenchymal cells were low in the inferior portion between the medial and lateral nasal processes.
5. Variable incomplete fusions such as the narrow inferior portion of the medial nasal processes toward the lateral nasal processes in fusion or a lack of fusion were observed.
6. All of these alterations may contribute to the pathogenesis of cleft lip induced by vincristine. Especially, median cleft lip may be due to the hypoplasia or aplasia of the frontal process, and lateral cle f t lip may be due to the hypoplasia of the lateral nasal process.
