RELATIONSHIP OF SECRETORY GRANULE CONTENT AND PROLIFERATIVE INTENSITYIN THE SECRETORY COMPARTMENT OF THE HAMSTER BRONCHIAL EPITHELIUM

We have previously shown that normal hamster airway epithelial secreto ry cells have a lower proliferative intensity than basal cells, but be cause of their high frequency are a major contributor to cell renewal (Am. J. Respir. Cell Mol. Biol. 1990; 2:51-58). In the present experim ent, the relation between proliferative intensity and secretory granul e content in bronchial epithelial cells is studied. [H-3]thymidine (2 muCi/g wt) was given intraperitoneally, 1 h before killing, to 5 hamst ers treated 21 days earlier with intratracheal saline and to six hamst ers in which secretory cell metaplasia had been induced by intratrache al treatment with 300 mug of human neutrophil elastase given 21 days e arlier. Light microscopic autoradiograms were prepared from 2-mum-thic k Epon sections of left intrapulmonary hilar bronchi. Cells were categ orized as basal, ciliated, secretory, or indeterminate. Secretory cell s were classified as either: S1, with 0 to 4 granules; S2, with greate r-than-or-equal-to 5 granules with intervening cytoplasm; or S3, with abundant granules and no apparent supranuclear cytoplasm. Proliferativ e intensity was defined by the categorical labeling index (LI(c)) at 1 h after [H-3]thymidine injection. LI(c) was determined by the number of labeled cells in a category as die percent of labeled and unlabeled cells of that category. LI(c) of each of the cell categories were sim ilar in the elastase and saline groups. LI(c) was highest for basal ce lls, reflecting their proliferative intensity, and lowest for ciliated cells. In the saline group, LI(c) of S1 (0. 25 %) was significantly h igher compared with S2 (0.13%); S3 cells were rare (0.2%) and none wer e labeled. In the elastase group, S3 cell frequency was 22% and their LI(c) (0.05%) was less than the LI(c) of S1 (0.21%) and S2 cells (0.59 %). We conclude that the proliferative intensity of bronchial secretor y cells is heterogeneous and that granule-rich secretory cells have an extremely low proliferative intensity. As with ciliated cells, this m ay be associated with a higher state of differentiation.