Glycogenolysis is biphasic during airway development in hamsters. The first glycogen depletion coincides with the appearance of endocrine cells, followed one day later by preciliated and presecretory cells. The second glycogen depletion coincides with functional maturation of the secretory cells. This suggests that energy derived from glycogen is required to establish the cell lineages early during development, and later is required for biosynthesis of membranes and organelles necessary for the onset of secretory cell functions. Impairment of glycogenolysis is a constant finding in the lungs of offspring of uncontrolled diabetic pregnancies associated with mild hyperglycemia. Such pregnancies are associated with increased incidences of 1) early growth delay and congenital malformations, and 2) respiratory distress syndrome due to delayed lung maturation. Since glycogenolysis appears to be functionally linked to two distinct phases of airway development (see above) it is anticipated that during diabetic hyperglycemic pregnancies, the early growth of fetal airways will be impaired and that maturation of secretory cells will be delayed. Conversely, it is anticipated that during hypoglycemic pregnancies, the early growth of fetal airways will be accelerated and that maturation of secretory cells will be hastened, compared with normal. The major goal is to compare and contrast the development of bronchi and bronchioles in fetal and neonatal hamsters developing during hyper-, hypo- and euglycemic pregnancies. Mild hyperglycemia will be induced in hamsters early in pregnancy by streptozotocin, and mild hypoglycemia will be induced by continuous infusion of insulin from a minipump. The diabetic model will be designed to create fetal hyperglycemia and hyperinsulinemia, and the hypoglycemic model will be designed to create fetal hypoglycemia and hypoinsulinemia (following development of the fetal pancreas).
The specific aims are to monitor intrapulmonary airway development by 1) measuring and analyzing three dimensional casts fo the airways in scanning electron micrographs; 2) quantifying mitotic indices and proportions of different epithelial cell types; 3) quantifying cellular differentiation using stereological methods; 4) demonstrating and mapping insulin receptors on epithelial cells using light and electron microscopic immunolabeling; and 5) evaluating secretory cell maturation by immunocytochemical demonstration of cytochrome P-450 reductase and Clara cell protein.
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