EFFECTS OF CORTICOSTEROIDS ON EPITHELIAL STRUCTURE AND SMOOTH-MUSCLE FUNCTION OF RAT TRACHEA

Corticosteroids, efficient drugs for the treatment of severe asthma, m ay have numerous side effects. We investigated the effects of 7 days o f treatment with triamcinolone (1.2 mg.kg(-1).day(-1)) on the epitheli al structure, tracheal smooth muscle cross-sectional area and contract ility in the rat. The corticosteroid-injected rats were compared to pa ir-fed, and pair-weighed animals. Histological studies were performed on transverse sections of glutaraldehyde-fixed tracheal blocks embedde d in plastic. In the preparations taken from corticosteroid-injected, pair-fed and pair-weighed animals, pharmacological stimulation with si ngle (10(-3) M) or cumulative (10(-8)-10(-3) M) concentrations of carb achol (in corticosteroid-injected and pair-fed animals), either inside (In or outside (Out of the tracheal lumen, was performed and contract ions of the tracheal smooth muscle were recorded. We found that triamc inolone administration: 1) reduced the number of epithelial cells and the tracheal smooth muscle cross-sectional area; 2) induced a decrease in maximal tension (Tmax (g); Out: 2.42 +/- 0.17, 1.03 +/- 0.1 in pai r-fed and corticosteroid-injected, respectively); In: 2.55 +/- 0.16, 1 .1 +/- 0.16, respectively) without affecting the sensitivity of the tr acheal smooth muscle; and 3) reduced the time required to reach 50% Tm ax in carbachol (In) preparations. We conclude that the observed chang es resulted from atrophy of tracheal smooth muscle induced by undernut rition and atrophy of tracheal smooth muscle and tracheal epithelium i nduced by corticosteroid treatment.