Developmental changes in glycoconjugate secretion by ferret tracheas

Surface epithelium and submucosal glands of the ferret trachea undergo extensive postnatal development. This study examined developmental changes in rates of release and types of high molecular weight glycoconjugates secreted by explanted ferret tracheas. Digestion with bovine testicular hyaluronidase separated the high molecular weight glycoconjugates into two types, hyaluronidase-resistant mucins and hyaluronidase-susceptible glycosaminoglycans. Release rates were measured under unstimulated conditions and in the presence of known secretagogues. The unstimulated rate of release of total ³H-glycoconjugates was 4-fold higher at birth than after complete maturation. The mucin content varied from 39 to 74% of total ³H-glycoconjugates; however, no age-related pattern was observed for mucin/glycosaminoglycan ratios. The rate of release of ³H-mucins was 6-fold higher at birth than in the adult but rapidly dropped to adult levels by 28 days of age. The secretory cells in the tracheal epithelium of newborn ferrets had more abundant rough endoplasmic reticulum than did mature goblet cells, suggesting increased synthesis of secretory product. Response to methacholine and trypsin, both known stimulators of mucin release, was not observed until 28 and 54 days of age, respectively. Incorporation of ³⁵S-sulfate into mucins relative to that for ³H-glucosamine increased with age, consistent with increasingly acidic histochemical staining properties of secretory cells. These developmental differences in rates of release, modulation of release, and relative sulfation of mucins may represent changes in secretory and synthetic mechanisms of the secretory cells.