We examined the effect of human recombinant TNF alpha on the potential difference (PD) and short circuit current (SCC) of canine tracheal epithelium using an Ussing chamber. Luminal or submucosal TNF (2 to 200 U/ml) produced no significant alterations in the basal PD or SCC values. Pretreatment with luminal TNF significantly reduced isoproterenol (ISOP, 10(-6) M)-evoked increases in SCC and PD to 57% and 66% of that with ISOP alone, respectively, with a significant decrease in conductance (G) to 87% of that with ISOP alone in a dose-dependent fashion, from 10 to 200 U/ml. Even after ISOP (10(-6) M)-evoked PD and SCC had reached a plateau, TNF produced significant decreases in PD and SCC up to 79% and 83% of that with ISOP alone, respectively, in a dose-dependent fashion, from 50 to 200 U/ml. Amiloride did not alter the inhibitory action of TNF on ISOP-evoked SCC and PD values. Antiserum against TNF abolished the inhibitory action of TNF on ISOP-evoked response. In contrast, submucosal TNF did not alter PD, SCC or G. These findings indicate that TNF attenuates beta agonist-evoked increases in chloride secretion across airway epithelium.