Effects of cyclic adenosine 3':5'-monophosphate-elevating agents and retinoic acid on differentiation in retinoid-deficient tracheal cultures.

The ability of cyclic AMP-elevating agents to induce normal differentiation has been investigated in retinoid-deficient hamster tracheal epithelium in organ culture. Dibutyryl cAMP (dbcAMP) and other cAMP-regulating agents alone caused disappearance of keratin and regeneration of normal mucociliary epithelium in retinoid-deficient cultures. Incubation of retinoid-deficient cultures with dbcAMP, isoproterenol, and cholera toxin (CT) (without addition of exogenous retinoid) reversed keratinization in a dose-dependent manner. The ED50 of cultures treated with dbcAMP was 4 X 10(-6) M; ED50 of isoproterenol was 7 X 10(-5) M; and CT, 0.6 micrograms/ml. Phosphodiesterase inhibitors and other cAMP analogs were inactive. Dibutyryl cAMP in combination with theophylline enhanced normal differentiation. Retinoid-deficient tracheas pretreated for 20 h with 10(-9) M all-trans-retinoic acid (RA) responded to 10(-6) M dbcAMP by potentiating normal differentiation; this concentration of dbcAMP alone was inactive. Isoproterenol showed a similar response but to a lesser degree. These cAMP-elevating agents applied in combination with theophylline did not increase activity.