Polyamines and putreanine relax respiratory tract smooth muscle in the guinea-pig

Spermidine, spermine, and putreanine, a metabolite of spermidine, caused transient relaxation of the isolated guinea-pig trachealis. The spermidine effect was not blocked by ouabain, propranolol or indomethacin. Spermidine treatment was shown to desensitize the tissue to subsequent additions of spermidine. After exposure to spermidine and repeated washes with spermidine-free solution, trachealis responded to KCl (30 mM) with a paradoxical relaxation. This relaxation was not blocked by propranolol, ouabain or indomethacin.