Changes in Secretory Cells of Hamster Tracheal Epithelium in Response to Acute Sublethal Injury: A Quantitative Study

Abstract

Secretory cells are reported to rapidly increase in number when the tracheobronchial epithelium is irritated. We suggest that this acute change results from accumulation of secretion granules within specialized albeit unobtrusive secretory cells rather than from conversion of undifferentiated cells to secretory cells or the production of new cells by mitosis. This hypothesis was tested in hamster tracheal epithelium 6, 12, and 24 hr after intratracheal instillation of elastase in saline or saline alone. Basal, secretory, and ciliated cells and cells of indeterminate character were quantified by counting 1400 cells per hamster in 2 μm thick glycol methacrylate sections stained with periodic acid—Schiff (PAS)—lead hematoxylin. Secretory cells were characterized and quantified depending upon distribution patterns of the PAS-positive secretion granules and on the amount of intracellular secretion product. Thirty-two hamsters were studied; half of them received colchicine 6 hr prior to tissue sampling. Over 24 hr the percentage of ciliated cells showed no significant change and no morphologic evidence of alteration was observed in this cell population; thus ciliated cells were excluded from the analyses. When the ciliated cell population was excluded, control and experimental values for the different cell categories remained statistically constant, if unavoidable classification errors at the light microscopic level were compensated for on the basis of ultrastructural features. Average control values for the non-ciliated cell population were: mitotic index 0.030, basal cells 27.8%, secretory cells 57.9%, and cells of indeterminate character 14.3%. Secretory product was decreased in secretory cells at 6 hr but thereafter secretion accumulated in these cells. At 24 hr the overall number of secretory cells appeared to be increased. However, the increase was apparent and not real and was accounted for by accumulation of secretion granules in preexisting but previously unobtrusive secretory cells.