EFFECTS OF FUROSEMIDE AND SALBUTAMOL ON HISTAMINE-INDUCED AND METHACHOLINE-INDUCED CONTRACTION OF THE ISOLATED GUINEA-PIG TRACHEAL CHAIN

The relaxant effect of furosemide on histamine- and methacholine-induc ed contraction was investigated in guinea-pig trachea in vitro with an d without epithelial cells. The isolated tracheas of four to six guine a-pigs were used in each experiment and suspended in organ baths, fill ed with Krebs-Henseleit solution and aerated with 95% O-2 and 5% CO2. Furosemide (3 x 10(-5) M) produced a relaxation of 65.3 +/- 9.0% after histamine-induced contraction and 101.2 +/- 3.9% (3 x 10(-4) M) after methacholine-induced contraction compared to salbutamol (100%). At hi gher concentrations furosemide produced a relaxation of 74.8 x 2.5% af ter 10(-4) M furosemide for histamine-induced contraction and 110.4 +/ - 5.3% (10(-3) M furosemide) for methacholine-induced contraction. Epi thelial cell removal had no effect on the relaxant effect of furosemid e for either agonist. Indomethacin pre-incubation (10(-6) M) also had no effect on the relaxant effect of furosemide for either agonist. The se findings suggest that epithelial cells and their mediators are not involved in the relaxant effect of furosemide, and that the products o f the cyclooxygenase pathway do not affect the smooth muscle relaxatio n caused by furosemide.