Carbohydrate histochemistry of rat respiratory glands

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Abstract
Cytochemical methods applied to examination of rat respiratory tract glands have revealed diversity of secretory complex carbohydrates. With the Alcian blue‐periodic acid Schiff (AB‐PAS) and the high iron diamine (HID) techniques at the light microscopic level, certain patterns of glycoprotein content were noted at various levels of the respiratory tract. Serous tubules and demilunes found in abundance in laryngeal and tracheal glands contained neutral glycoprotein. Mucous tubules found in abundance in epiglottal and laryngeal glands and in lesser number in tracheal glands most often produced sulfated glycoprotein. However, mucous tubules in epiglottal and tracheal glands contained a few cells with sialylated glycoprotein, and mucous tubules in some areas in laryngeal glands contained mainly cells producing sialylated glycoprotein. Mucous ducts found in abundance in lower laryngeal and tracheal glands formed mainly sialylated glycoprotein and contained infrequent cells with sulfated glycoprotein. The type of glycoprotein found in each cell type by light microscopy was confirmed at the ultrastructural level by the periodic acid‐thiocarbohydrazide‐silver proteinate (PA‐TCH‐SP), dialyzed iron (DI) and high iron diamine (HID) methods. Serous cell granules displayed light reactivity with the PA‐TCH‐SP method and no DI or HID affinity and were judged to contain sparse neutral glycoprotein. Serous granules disclosed negative central foci with the PA‐TCH‐SP method. Granules of most mucous tubule cells stained strongly with the PA‐TCH‐SP and HID procedures and contained abundant sulfated glycoprotein. Occasional mucous tubules stained with the PA‐TCH‐SP but not with the HID method and apparently corresponded with cells judged to form sialylated glycoprotein from their blue staining with the HID‐AB sequence. Two zones within individual granules in some cells revealed different HID staining intensity and appeared to differ in the amount or kind of sulfated glycoprotein they contained. Some cells exhibited granule heterogeneity containing both HID‐positive and unstained granules. Spherical cores present in granules of mucous tubules below the upper laryngeal level occasionally appeared bizonal and invariably lacked reactivity demonstrative of complex carbohydrate. Mucous duct cell granules stained heavily with the PA‐TCH‐SP and DI methods and reacted infrequently with the HID procedure and were considered generally to contain sialylated glycoprotein, and occasionally to form sulfated glycoprotein. The three carbohydrate stains distinguished a heavily and a moderately reactive zone in the cortex outside the monophasic or biphasic, carbohydrate‐free cores in granules of some mucous duct cells.