A Study on the Effects of Retinoic Acid on the Epithelium of Palatine Process in Albino Rat Fetus

The elevation and fusion of palatine are essential processes in the completion of the palatal development. It is believed that the mesenchyme plays a major role in the ascent of the palatal process, and that the palatal epithelium is involved in its fusion. The mechanism of fusion requires several different morphologic and molecular changes prior to the completion of the mesenchymal continuity between different palatine processes. The mechanism of removing the epithelial cells from the fusion zone could include either programmed cell death, epithelial-mesenchymal transformation or migration to adjacent epithelia. Retinoic acid has been known to induce cleft palate by disturbing mesenchymal growth and/or epithelial fusion. The effect of retinoic acid on the epithelium of the palatine process was studied in the fetus of the Sprague- Dawley rat with feeding 100 mg/kg of retinoic acid mixed in olive oil on the 10th day of fetal age and controlled with feeding pure olive oil. The epithelium of the palatine process was examined by PAS reaction and electron- microscopy on the 14th, 15th, 16th and 18th day of fetal age. The obtained results were as follows: 1. In the control group, glycogen was plentiful at the entire epithelium of the palatine process during the pre-fusion period(14th and 15th day), but it diminished in contact epithelium at the fusion stage(16th day). On the contrary, in the experimental group treated with retinoic acid, glycogen was plentiful and did not change from the 14th to 18th day of gestation. 2. In the control group at fusion stage(16th and 18th day), PAS-positive cells increased in the nasal and oral epithelium adjacent to the fusion site, and in the mesenchyme around the fusion site. 3. As a result of electronmicroscopic findings, the epithelium in the experimental group with retinoic acid seemed to be injured by retinoic acid; RER was composed of flattened cisternas and ribosomes were detached, mitochondrial crista and membrane were destructed and sacculated, and Golgi complex was extremely atrophied. According to the results, it seems that apoptosis as well as cell migration and transformation happen in the mechanism of cleaning the epithelium at the contact site, and that retinoic acid injures directly intracytoplasmic organelles and disturbs apoptosis, a sort of normal developmental process. More studies should be done to verify relations between apoptosis and large-sized glycogen granule in superficial epithelium.

An Immunohistological and Immunogold Study on the Fibronectin Reacions in Rat Lung Differentiation / 대한흉부외과학회지

BACKGROUND: Fibronectins(FN) are large, dimeric glycoproteins present in the plasma, loose connective tissues, and some basal lamina in vivo and synthesized by a number of cells in vitro, including lung fibroblasts, and alveolar macrophages. FN can affect the migration, proliferation, differention, and even apoptosis of various cell types, all considered necessary for organogenesis. This study was undertaken to detect the changes of localization and activity of FN, a glycoprotein molecule, in stages of lung differentiation in rats. MATERIAL AND METHOD: The experimental animals(Sprague-Dawley strain) were divided into 8 groups, a control group(adult male rats), and experimental groups of 17th day fetus, 20th day fetus, first day newborn, second day newborn, 3rd day newborn, 5th day new born, 7th day newborn. We used the immunohistological stain method with gold particle to obtain the data for distribution of FN in the alveoli, blood vessels, terminal bronchioles, alveolar macrophages and type II pneumocytes. This study revealed the FN reactions at the light and electron microscopic levels. RESULT: At 17th day fetal stage, FN reactions in fetal lung were strong on the blood vessels and moderate on the stroma. At 20th day fetal stage, FN reactions were strong on the blood vessels. After birth, FN reactions in alveolar basement membrane were maximum in the 5th and 7th day newborns. FN reactions in the blood vessels were observed to be moderate in first and second day newborns, but decreased in third day newborns. FN reactions in alveolar macrophages increased after birth. FN reactions in terminal bronchioles gradually increased after birth. 6. In type II pneumocytes, FN reactions were observed to be moderate in 1st and 3rd day newborns. CONCLUSION: Immunohistochemical analysis of rat lungs at various developmental stages revealed increased deposition of FN during the pseudoglandular stage of lung development, coinciding with the period of branching morphogenesis. Also, FN is released from type II pneumocytes. This observation, together with the strategic location of FN, suggests a role in airway formation.