Lack of an effect of saxitonin on the contractility of isolated guinea-pig trachea, lung parenchyma and aorta

The effects of saxitonin were investigated in guinea-pig tracheal rings, lung parenchymal strips and aorta rings. Tracheal rings were used both with epithelium present and with it removed. Aorta rings were used both with endothelium present and with it removed. Saxitoxin, 1 pM to 0.1 μM, did not alter the resting tension of either airway tissues or aorta. Also, 0.1 μM saxitonin did not reduce tension of tracheal rings contracted by 10 μM carbachol, parenchymal strips contracted by 100 μM acetylcholine or by 10 μM histamine, or aorta rings contracted by 10 μM norepinephrine. Responses of tracheal rings to 0.03–10 μM carbachol added cumulatively were not altered by 0.1 μM saxitoxin (EC 50 with epithelium: 1.11± 0.48 μM control, 2.01 ± 0.71 μM with saxitoxin; EC 50 without epithelium: 2.83 ± 0.55 μM control, 2.05 ± 0.58 μM with saxitoxin). Also, 1 μM saxitoxin did not alter contractions of parenchymal strips to cumulatively added acetylcholine (EC 50: 3.47 ± 1.06 μM, control; 3.98 ± 1.19 μM with saxitoxin), histamine (EC 50: 0.83 ± 0.24 μM, control; 0.60 ± 0.13 μM with saxitoxin); or of aorta strips to norepinephrine with endothelium (EC 50: 1.78 ± 0.80 μM, control; 0.74 ± 0.21 μM with saxitoxin) or without endothelium (EC 50: 2.18 ± 0.78 μM, control; 1.42 ± 0.62 μM with saxitoxin). Thus, saxitoxin did not significantly alter contractile activity of airways of large arteries in vitro.