Squamous Metaplasia of the Tracheal Epithelium in Organ Culture. II. Nutritional Influences

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Abstract
The mucociliary epithelium of the adult hamster trachea undergoes squamous metaplasia in organ culture when maintained in a complex, chemically-defined medium (Waymouth''s MAB 87/3) without serum. This change fails to develop in explants cultured in Eagle''s minimum essential medium (MEM). To determine the factors promoting squamous metaplasia, nutritional constituents in Waymouth''s MAB 87/3 medium but not present in MEM were divided into 5 goups: insulin and glutathione; vitamins C, B12 and biotin; nucleic acid intermediates; inorganic salts; and nonessential amino acids. Test media were formulated by adding each group or combinations of groups to Eagle''s MEM. Organ cultures were maintained in the test media for 4 wk and then examined histologically. The nonessential amino acids were most important in enhancing metaplasia and keratinization. When nonessential amino acids were added individually to MEM, L-glutamic acid and L-serine seemed most influential in inducing metaplastic changes.